Techniques for Cultivating One-Year-Old Seedlings and Large Seedlings of Photinia × fraseri by Cuttage

  Photinia × fraseri is also known as Flame Red, Qiannian Hong, Red Robin, Red Lip, Sour-Leaf Photinia, and Sour-Leaf Tree. It is mainly distributed in the subtropical and temperate regions of southeastern and eastern Asia and North America, and is now cultivated in many parts of our country. Its flowering period is from May to July, and its fruit ripens from September to October. It is mainly used in gardens as hedges or as street trees.

  1 Cultivation of One-Year-Old Photinia × fraseri Seedlings

  1.1 Nursery Site Selection and Land Preparation

  Choose sandy soil with convenient drainage and irrigation, loose texture, and moist fertility, with rice as the previous crop, as the nursery site. Avoid planting in low-lying plots with poor drainage and poor air permeability.

  1.2 Cutting Time

  In Jiangxi, the cutting time is from May to June, that is, when the new shoots sprouted by the current year's Photinia × fraseri mother trees change from red to green. At this time, cuttings heal quickly and root easily. The nursery land should be broken up and refined. Before land preparation, apply base fertilizer (compound fertilizer at 40 kg per 667 sq m, and cake fertilizer at 50 kg), and the land can be broken up and turned into the soil with a tractor or diesel rotary tiller. Make the beds 20 days before cutting (1 m wide, 30 cm high). After the beds are made, spray the bed surface and footpath ditches with dinitroaniline at 500 g per 667 sq m mixed with 70 kg of water and a 0.5% potassium permanganate solution to reduce weed growth and disinfect the soil. After the seedbeds are made, cover them with plastic film for later use.

  1.3 Mother Tree Selection

  Choose the variety you like, with mother trees aged 10 to 15 years old and in their prime, and require that the mother trees develop normally, grow robustly, and be free of pests and diseases.

  1.4 Branch Selection

  Choose thick and strong branches growing in the middle and upper parts of the canopy. Such branches have strong vitality and are the easiest from which to propagate new plants.

  1.5 Branch Cutting

  Choose overcast and rainy days or early morning when there is dew for pruning. After pruning, immediately wrap the branches in a wet cloth and place them in a cool place to prevent water loss. Keep the branches 6 to 10 cm long and about 0.3 cm thick. The upper end of the branch should be cut flat, and the lower part should be cut obliquely. The cut should be smooth and level. Keep 0.5 to 1 leaf on the upper end of the branch and cut off the rest. Soak the base of the prepared cuttings in a mixed solution of fresh yellow mud slurry and ABT rooting powder at 200 mg/L for 1 to 2 hours. This helps promote new root development and improves the survival rate.

  1.6 Cutting

  When cutting, pay attention to keeping the cuttings moist. First use a bamboo stick to make slanted holes in the seedbed, then insert the cuttings into the holes. The depth into the soil should be about one-half the length of the cutting. After that, use both hands to press the soil and squeeze it tightly toward the center of the cutting. After all cuttings are inserted, water thoroughly, then spray with a 500-fold solution of thiophanate-methyl or carbendazim for sterilization. Immediately afterward, build a frame with bamboo strips or wooden strips and cover it with a shade net to make a shade shed. The shed height should be 80 to 100 cm above the bed surface. For the shading degree of the shade net, choose a three-pin 70% one or use two layers of a two-pin one. At the same time, cut, water, and shade as you go, to avoid water loss from the cuttings themselves.

  1.7 Management After Cutting

  1.7.1 Control of humidity and temperature: After cutting, according to rainfall conditions and the dryness or moisture of the soil, water once a day as needed to keep the soil moist. The most suitable temperature for Photinia × fraseri cuttings is 25°C. When the temperature exceeds 35°C, the cuttings are prone to drying out and withering, so a shade net should be set up to control the temperature and increase the humidity inside the shed.

  1.7.2 Light control: About 30 days after cutting Photinia × fraseri, the base begins to heal and new roots grow. After that, gradually remove the shade net, and remove it completely after October, in order to speed up lignification and enhance wind and cold resistance.

  1.8 Fertilization

  From August to September, apply topdressing 2 to 3 times. Dilute human feces and urine can be applied lightly, generally 1 ladle of human feces and urine mixed with 1 bucket of clear water, or 0.2 kg of compound fertilizer mixed with 50 kg of water, fully dissolved and stirred before watering.

  2 Large Seedling Cultivation

  2.1 Nursery Site Selection, Land Preparation, Base Fertilizer Application, and Bed Making

  Transplant before the new shoots sprout around the Beginning of Spring. When lifting seedlings, use a hoe or toothed rake. Collect and bundle the seedlings by grade according to first-grade and second-grade seedlings. When planting, plant first-grade and second-grade seedlings separately. This helps produce seedlings that grow evenly, with little differentiation, and promotes more and denser lateral fibrous roots. Prune branches and leaves appropriately according to the growth condition of the tree. When planting, make sure they are upright, the roots are spread out, and the soil is pressed firm. The planting depth should be appropriate, generally 3 to 5 cm deeper than the seedling root collar. After planting, water thoroughly to settle the roots.

  2.2 Management After Planting

  After planting, combine weeding with shallow tillage and loosening of the soil using a small hoe. For fertilization, apply decomposed dilute human feces and urine. In the first half of the year before June, apply 4 to 5 times; after September in the second half of the year, apply 2 to 3 times. At the same time, compound fertilizer can also be applied in holes, 30 to 40 g per hole, and covered with soil after application. Pruning and pinching are carried out according to the plant's growth condition, mainly to promote lateral branches and make the tree fuller.

  After 3 to 4 years of cultivation, Photinia × fraseri can reach a seedling height of 1.5 to 2 m. It can then be transplanted again with soil, and the branches, leaves, and canopy can be pruned appropriately, or the cultivation period can be decided according to market demand.

Market Value and Market Potential of Photinia × fraseri

Photinia × fraseri may be one of the most well-known nursery stock varieties on the market at present. With vigorous advertising and promotion led by several large production enterprises headed by Zhejiang Senhe Seed Industry Co., Ltd., it quickly became a household name in the nursery stock industry. However, because there are still many unclear factors in the Photinia × fraseri market, many industry players remain hesitant about it. A reporter conducted a market survey on this issue for the reference of nursery stock workers.

Photinia × fraseri Emerges to Meet the Trend

Photinia × fraseri only began to become gradually known to people starting last year. In the eyes of many people, it seems to have been "born rich and noble": as soon as it entered the domestic market, it "shot to fame." In fact, like many other nursery stock varieties, the "good days" of Photinia × fraseri were also waited for.

Nanjing Wanhe Photinia × fraseri Nursery began small-scale cultivation of Photinia × fraseri 8 years ago and is one of the earliest production units in the country. Ji Guoping, general manager of the nursery, said that Photinia × fraseri in Nanjing was initially introduced from Japan by a local research institution. After seeing it, he thought it was very beautiful, so he planted some in the nursery. In the first few years, Wanhe did not promote Photinia × fraseri much and only carried out a small amount of propagation each year. It was not until two years ago, when enterprises in the market advertised and promoted Photinia × fraseri, that Wanhe consciously expanded the propagation quantity of seedlings.

Jiangsu Xinghuo Lawn Joint Development Company introduced a batch of Photinia × fraseri from Europe as early as 1999, and only began supplying seedlings to the market in batches in the past two years. Wang Fuyin, general manager of the company, said that on the one hand this was because after introducing a new variety it was necessary to observe and test it for two years, and on the other hand because colored-leaf tree species have only become popular in recent years, and demand was not large before.

Following Nanjing Wanhe and Xinghuo Lawn, Senhe Seed Industry, Shanghai Luya Landscape Engineering Co., Ltd., and Zhejiang Yuyao Ruanyi Seed Industry Co., Ltd. also successively introduced and propagated Photinia × fraseri. What these introduction units said in common was that the attention Photinia × fraseri has received is closely related to the current situation of garden greening construction in our country.

Urban greening in our country is now mainly green, making the colors appear rather monotonous. In order to change this situation, many cities have put forward the slogan of "colorization and beautification." Zheng Yongping, chairman of Senhe Seed Industry Co., Ltd., said that greening construction in our country has changed from simply building green to colorizing and beautifying cities. The proportion of colored-leaf trees in cities will gradually increase, and is expected to reach 15-20%. If calculated according to the country's annual addition of 20,000 hectares of urban green space, the demand for colored-leaf seedlings would be 4,000 hectares, which is a very large number. Moreover, at the current stage, the share of colored-leaf seedlings in the market is still especially small, the number of native arbor species is also not large, and many shrub varieties imported from abroad are still in the propagation stage. These objective conditions determine that excellent colored-leaf tree species have huge market prospects.

A Rare Red-Leaf Tree Species

There are hundreds and thousands of colored-leaf tree species in the world. Why does everyone keep their eyes fixed on one Photinia × fraseri?

Ji Guoping said that when staff from the Nanjing Garden Bureau went to Japan on an inspection tour that year, they did not take a liking to Japan's national flower, the cherry blossom, but brought back Photinia × fraseri. Zheng Yongping and Tian Di, general manager of Luya Company, also said that the first thing they took a liking to abroad was Photinia × fraseri. At present, among red-leaf shrub varieties, no other particularly good variety has been found besides Photinia × fraseri. Tian Di has done greening projects for many years. From the perspective of a user, he explained the four major advantages of Photinia × fraseri. First, the landscape effect is good. Photinia × fraseri is an evergreen colored tree species. In East China, its red-leaf period lasts as long as 8 to 9 months in a year, and the color is bright and long-lasting, which is very rare among evergreen colored-leaf tree species. Second, its propagation technology requirements are not high, making it relatively easy to promote. Third, Photinia × fraseri is widely used in greening. It grows fast and tolerates pruning. It can be used for color blocks and color hedges, and can also be cultivated into arbor trees with a single trunk and spherical canopy. It can both form a landscape on its own and serve as an accent. Fourth, Photinia × fraseri has strong adaptability, tolerates low temperatures, tolerates poor soil, and has a certain tolerance to salinity-alkalinity and drought. It likes strong light and also has strong shade tolerance, and the suitable growing area is extensive.

Zheng Yongping said that before Senhe decided which nursery stock to produce, it had investigated more than 8,000 varieties at home and abroad, and finally selected 212 species. After 3 years of testing, it found that among these varieties, the comprehensive performance of Photinia × fraseri was particularly outstanding. He said that Photinia × fraseri has been developed in New Zealand for 40 years and used in Europe, America, and Japan for more than 20 years. It is a widely welcomed mature tree species and is known as the "king of red-leaf hedges." This was also an important reason why Senhe initially chose Photinia × fraseri.

Judging from feedback from the greening project market, Photinia × fraseri has already been recognized by many units. Tangshan Haomen Garden Company even advertised in the newspaper, exclusively purchasing Photinia × fraseri.

Key Issues Difficult to Settle

Now, even slightly larger nurseries all know about Photinia × fraseri, but very few dare to introduce it in large quantities. Most people are still in a state of "holding their money and waiting to buy." People are mainly concerned about two issues: How many seedlings of Photinia × fraseri are there now? How large is the demand, really?

Photinia × fraseri propagates very quickly. One one-year-old mother plant can generally propagate 30 to 40 plants in a year. If these propagated seedlings are then used to continue propagation, two years later there would be more than 1,000 plants. The increase in quantity is astonishing, so clarifying the current base number of Photinia × fraseri has great reference value. It is very difficult to accurately count this number because many nursery stock enterprises treat it as a commercial secret. Some also arbitrarily exaggerate the number for promotional purposes, so there is a great deal of false information. According to estimates by Zheng Yongping and Tian Di, the current number of Photinia × fraseri seedlings is probably between 10 million and 20 million, and finished seedlings are around 1 million. These two figures may deviate, but it is a fact that the number of Photinia × fraseri seedlings and finished seedlings is not large. First, there are not many enterprises currently producing Photinia × fraseri on a scale. The introduction sites of enterprises in Shandong, Henan, and other places are basically the same, concentrated in several nurseries that introduced Photinia × fraseri earlier, such as those in Nanjing, Hangzhou, Jurong, and Shanghai. The products of enterprises producing tissue-cultured Photinia × fraseri seedlings in Shenyang, Dalian, Anshan, and other places are basically sold to Jiangsu and Zhejiang. Second, the price of Photinia × fraseri seedlings is high. A small seedling of more than 10 cm sells for 3 to 5 yuan, which limits introduction by nurseries lacking financial strength. Now nurseries are becoming more and more cautious in introducing varieties. For a new variety like Photinia × fraseri, they generally only buy eighty or a hundred plants on a trial basis. Finally, the earliest units working with Photinia × fraseri are all unwilling to sell large seedlings more than one year old, and mostly keep them as mother plants for propagation. From this, it can also be seen that the current number of mother plants is limited. As for project seedlings, the shortage in the market is currently very obvious, which can be roughly seen from the price of up to ten yuan or more per one-year-old seedling and from the fact that user units advertise to find seedlings.

Berberis thunbergii var. atropurpurea and Loropetalum chinense var. rubrum are currently the main tree species used for hedges and color blocks in urban greening, with very large usage, exceeding 1 billion plants every year. When promoting Photinia × fraseri, production enterprises like to compare it with Berberis thunbergii var. atropurpurea and Loropetalum chinense var. rubrum, and say that in the near future Photinia × fraseri will replace the latter. Their reason is that the leaves of Berberis thunbergii var. atropurpurea and Loropetalum chinense var. rubrum have a low degree of leatheriness and are dark purplish-red in color. In addition, Berberis thunbergii var. atropurpurea sheds its leaves in winter, and Loropetalum chinense var. rubrum is only suitable for planting in acidic soil. In ornamental effect and adaptability, they cannot compare with Photinia × fraseri.

However, some industry insiders consider this comparison inappropriate. Liu Yalong admits that Photinia × fraseri is a very good variety and has great potential in the Jiangsu-Zhejiang region. He also said that it is best to compare nursery stock varieties within the same species and genus, and that Berberis thunbergii var. atropurpurea is something that has already been promoted and widely accepted by user units. In high-latitude areas, its cold tolerance is still beyond what Photinia × fraseri can match at present. Liu Yalong said: "What nursery stock is used in greening projects mainly depends on two points: landscape effect and price. Now the cutting seedlings of Berberis thunbergii var. atropurpurea cost about one mao per plant, and project seedlings are just over one yuan. Compared with Photinia × fraseri, the price advantage is obvious." Hou Boxin, a research expert on Loropetalum chinense var. rubrum and associate researcher at the Hunan Academy of Forestry, also emphasized the price advantage of Loropetalum chinense var. rubrum, whose project seedlings cost less than one yuan per plant, and moreover the flowers of Loropetalum chinense var. rubrum are very beautiful, which Photinia × fraseri cannot match. Hou Boxin has now bred a variety of Loropetalum chinense var. rubrum with relatively strong cold tolerance and is preparing to take it to Beijing for trial planting.

Northern Limit of Introduction Still Unclear

What determines the market size of a nursery stock variety, apart from its own traits, is also the suitable planting range. So how wide is the planting range of Photinia × fraseri in the country? A common saying is that it can be planted in areas east of Xi'an and south of Beijing, but the reporter heard different views during the survey.

On the nursery stock variety display page of the website of Beijing Forestry University Forestry Technology Co., Ltd., Photinia × fraseri is listed first, but Qiao Zhuanyun, manager of the company, told the reporter affirmatively, "Photinia × fraseri won't work in Beijing; the cost of overwintering is too high." He said that they tried it two years ago and found that it needed a small arched shed to overwinter, so now they basically do not do it.

Northeast Normal University Forest Biotechnology Company began producing tissue-cultured Photinia × fraseri seedlings in 2001 and had trial plantings in Beijing, Dalian, Shandong, and Henan. According to Zhang Yifei of the company, Photinia × fraseri freezes rather severely in winter in Beijing and Dalian and cannot overwinter in the open field. Some areas of Shandong are also similar to Beijing. Now their tissue-cultured seedlings are mainly sold to the Jiangsu-Zhejiang region.

Zhu Shaoyuan, general manager of the Changyi Flower and Tree Farm in Shandong Province, said: "Photinia × fraseri is planted quite a lot in Hokkaido, Japan. If considered by latitude, Shandong should also be able to plant it. But from trials in recent years, it can overwinter south of Jinan, while it cannot in northern Shandong areas such as Weifang and Dezhou. To promote it in Shandong, it needs to be introduced step by step, first from Nanjing to Henan, then from Henan to Shandong. In this way, it may succeed."

Winter temperatures in Henan are higher than in Shandong, and domestic Photinia glabra and Photinia davidsoniae grow very well there. Liu Yalong of Henan Province Lushan County Wanchun Landscape Greening Co., Ltd., who began trial planting Photinia × fraseri 4 years ago, said that the overall performance of Photinia × fraseri in Henan is acceptable. The newly grown tender shoots are very beautiful, but there are also some problems. He found that Photinia × fraseri introduced from different units differed greatly in traits. The variety he first introduced from Nanjing Zhongshan Botanical Garden was very cold-tolerant, while the variety introduced from a Shanghai enterprise last year showed tip drying in winter. Liu Yalong said: "At the time the impact was not great; simply covering it with a small arched shed was enough. But when the film was removed this year, aphids were found inside damaging the tender shoots." It can be seen that in areas such as Hebei, Shandong, Shaanxi, and Shanxi, special caution is needed when introducing Photinia × fraseri.

The introduction of varieties is a complex issue. Differences in planting techniques and among varieties may also lead various units to draw different conclusions. Taking the situation in various places together, a prudent statement is: at present, planting Photinia × fraseri south of the Yellow River is relatively reliable.

Opportunity and Risk Coexist

The overwhelming advertising and promotion of Photinia × fraseri easily reminds people of the former fast-growing poplar. Some people believe this promotion method is debatable.

Zhu Shaoyuan said that nursery stock varieties are not consumer goods; it is not enough just to build a brand. Nursery stock are living organisms, and many factors affect their growth. The best way to promote them is to grow a patch and let everyone see it. Publicity alone is not enough. Zhang Qi, general manager of Haomen Company, believes that Photinia × fraseri has good color and is a new variety, and many people are interested in it, but to what extent it can finally be applied is still hard to say. He said: "In the process of using a new variety, problems may arise, or it may go very smoothly. These are unknown. Generally speaking, a variety needs at least 5 years of testing before it can be used with confidence. At present, Photinia × fraseri can only be said to be roughly acceptable, and still needs to be tested by nature."

Senhe Seed Industry, however, is full of confidence in Photinia × fraseri. In order to let more greening project units understand Photinia × fraseri, the enterprise also carried out a "Double One Hundred Demonstration Project." Zheng Yongping said: "There are now very few units with pure varieties and technical strength. As propagation volume increases and technology becomes increasingly widespread, there is great room for price reduction in Photinia × fraseri project seedlings, and it can completely reach the level of Berberis thunbergii var. atropurpurea and Loropetalum chinense var. rubrum." He predicts that for 5 to 8 years, Photinia × fraseri will be a variety with relatively high profit. The current key is to push Photinia × fraseri into the project market as soon as possible, thereby stimulating the seedling market.

Driven by interests, many people are eager to try, but the unclear market status of Photinia × fraseri and its overly fast propagation speed make them hesitate.

As the saying goes, opportunity always favors those who are perceptive, but there is a hidden sentence left unsaid: risk is the twin brother of opportunity, and the two go hand in hand.

Given that current market information about Photinia × fraseri is incomplete, decision-making has a certain game-like nature. Whether one is suited to develop Photinia × fraseri still requires each nursery to decide according to its own actual situation.

Vegetative Propagation of Nursery Stock -- Green Branch Cuttage

Vegetative Propagation of Nursery Stock -- Green Branch Cuttage

Vegetative propagation is a seedling-raising method that uses plant vegetative organs such as branches, roots, stems, and leaves to cultivate an independent individual under suitable conditions. Because vegetative propagation does not involve sexual cells, it is also called asexual propagation. Seedlings cultivated by vegetative propagation methods are called vegetative propagation seedlings or asexual propagation seedlings.

Vegetative propagation is also a seedling-raising method that uses the regenerative capacity and meristematic capacity of plant cells and their grafting compatibility with another plant. Regenerative capacity refers to the ability of a part of a plant vegetative organ (root, stem, leaf) to differentiate and form other parts that it originally did not have, such as using a stem or branch cutting to grow new leaves and new roots, using a root cutting to grow new branches and new leaves, and using a leaf cutting to grow new roots and new stems. Meristematic capacity refers to the ability of some plants to grow special metamorphosed organs specifically for vegetative propagation, such as corms, bulbs, and stolons.

vVegetative propagation has the following characteristics:

v① It can maintain the excellent traits of the mother plant. Because vegetative propagation is not produced through the combination of sexual cells, but by somatic cells directly divided by meristematic tissue, all the genetic information of the parent can be reproduced, so it can maintain the excellent traits and inherent phenotypic characteristics of the original mother plant, without producing the trait segregation seen in seed propagation. This achieves the purpose of preserving and propagating excellent varieties.

v② Seedlings from vegetative propagation generally grow fast and can flower and bear fruit earlier. This is because the new plant from vegetative propagation is a continuation based on the original developmental stage of the mother plant, unlike seed-propagated seedlings, whose individual development starts anew.

v③ Some garden plants do not bear fruit, bear little fruit, or do not produce viable seeds, so vegetative propagation can be used for seedling raising, improving the effectiveness of seedling production and the propagation coefficient. Examples include double-flowered ornamental peach and seedless fruits.

v④ Some garden plants with special forms need to be propagated and produced through vegetative propagation, such as tree-form roses and Sophora japonica 'Pendula'. Moreover, the rejuvenation of ancient and famous trees in gardens also requires promoting tissue proliferation or restoring their growth vigor through grafting (top grafting or bridge grafting).

v⑤ The method is simple and economical. Because the seeds of some garden plants have deep dormancy, seed propagation is relatively cumbersome and difficult, while vegetative propagation is easier, simpler, and more economical.

vFrom the above, it can be seen that vegetative propagation plays a very important role in garden seedling raising, plant shaping, and the rejuvenation of ancient and famous trees. However, vegetative propagation also has its shortcomings. For example, the root system of vegetatively propagated seedlings has no obvious taproot and is not as developed as that of seedling-grown plants (except grafted seedlings), with poorer resistance and a shorter lifespan. For some tree species, repeated vegetative propagation over multiple generations can easily cause degeneration, resulting in weak seedling growth, such as in Chinese fir.

vCommonly used methods of vegetative propagation in the cultivation of garden nursery stock include: cutting propagation, grafting propagation, division propagation, layering by burying stems, and layering propagation.

Section One Cutting Propagation

vCutting propagation is a propagation method that uses part of a detached plant vegetative organ such as root, stem (branch), or leaf, inserts it under certain conditions into soil, sand, or another substrate, and uses the plant's regenerative capacity to develop it into a complete new plant through artificial cultivation. The part cut for direct cutting is called a cutting, and the seedling obtained by cutting propagation is called a cutting seedling.

vCutting propagation is simple, has abundant material, and can carry out large-scale seedling production and multi-season seedling production. It has become one of the main propagation means for trees, especially rare garden tree species that do not bear fruit or bear few fruits. Like other vegetative propagation, cutting seedling raising has the characteristics of fast seedling formation, old stage development, and maintaining the excellent traits of the mother plant. However, because the cuttings are separated from the mother body, suitable environmental conditions such as temperature and humidity must be provided for them to survive. For some tree species with higher requirements, necessary measures such as shading, misting, and building plastic sheds are also needed for success. Therefore, cutting propagation requires fine management and is relatively labor-intensive.

1. Principles of Cutting Survival

(1) Rooting Types of Cuttings

vThe rooting of plant cuttings is called adventitious rooting because there is no fixed attachment position. The key to cutting survival is the formation of adventitious roots, and adventitious roots originate in groups of meristematic cells. The origin sites of these meristems differ greatly and vary with plant species. According to the site of adventitious root formation, there are 2 types: one is the bark rooting type, which mainly roots from the bark, sending out many adventitious roots from the lenticels, nodes (buds), and other parts of the bark all over the cutting. The other is the callus rooting type, which mainly roots from callus, sending out many adventitious roots from the basal callus (or healing tissue), or from stem nodes adjacent to the callus. These 2 rooting types have different rooting mechanisms and therefore differ in rooting difficulty. However, many tree species root in an intermediate condition, that is, a comprehensive rooting type, in which the amounts of callus rooting and bark rooting differ relatively little, such as poplar, grape, oleander, golden-edged privet, and photinia.

v1. Bark rooting type Cuttings belonging to this type all have root primordia or root initials located at the intersection of the widest part of the medullary ray and the cambium. This is because the cambium undergoes cell division, differentiates outward into blunt conical root primordia, invades the phloem, and leads to the lenticels. During the outward development of the root primordia, the medullary ray connected to it also gradually thickens, passes through the xylem toward the pith, and obtains nutrients from the pith cells. This kind of bark rooting is relatively rapid, has a wide rooting area, and has no connection with healing tissue. Generally speaking, this bark rooting type belongs to easy-to-root tree species.

v2. Callus rooting type In cuttings of this rooting type, the formation of adventitious roots must be completed through the differentiation of callus. First, a group of thin-walled cells that is translucent and has obvious nuclei forms on the surface of the lower cut of the cutting; this is the primary callus. The primary callus cells continue to differentiate and gradually form tissues such as xylem, phloem, and cambium connected with the corresponding tissues of the cutting. Finally, after full healing, roots differentiate from the callus under suitable temperature and humidity conditions. Because this kind of rooting takes a long time and grows slowly, tree species that are difficult to root by cutting and root slowly mostly root from callus.

vIn addition, after the cutting survives, the first bud (or second bud) from the upper part sprouts and grows into a new stem. When the base of the new stem is buried by the substrate, adventitious roots often grow, and these roots are called new-stem roots. For example, poplar, willow, plane tree, edgeworthia, and flowering pomegranate can promote new-stem rooting, thereby increasing the number of roots and improving the yield and quality of seedlings.

Bark rooting type Callus rooting type

Image 2

Positions where adventitious roots are produced

vIn studying the theory of cutting rooting, many scholars have done a great deal of work, put forward many views from different angles, and used them to guide cutting practice, achieving certain results. These views are briefly introduced below:

v1. Auxin viewpoint This holds that plant cutting rooting and callus formation are controlled and regulated by auxin, and cytokinins and abscisic acid are also related to some extent. Auxin synthesized by the branch itself can promote root system formation. It is mainly synthesized in the young buds and leaves of the branch and then transported toward the base, participating in root system formation. Production practice has proved that when people use young plant shoots for cutting propagation, their endogenous auxin content is high and cell meristematic capacity is strong, making cuttings easy to survive. Grape cuttings themselves do not have latent root primordia. When grape cuttings are inserted with leaves, their root systems are very developed. If the buds and leaves are removed in advance, rooting ability is significantly affected, or they may not root at all. This shows that there is an important substance affecting cutting rooting, namely that plant leaves and buds can synthesize natural auxin and other effective rooting substances and transport them downward through the phloem to the base of the cutting. This indicates a polar transport from the top to the base, and also shows that the base of the cutting is the most active place for promoting root formation.

vAmong auxins, auxin a, auxin b, and indoleacetic acid (IAA) have been discovered. This provides a basis for humans to use plant endogenous auxins and artificially synthesized exogenous auxins to promote adventitious root formation at the base of cuttings. At present, those used in production include indolebutyric acid (IBA), indoleacetic acid (IAA), naphthaleneacetic acid (NAA), naphthaleneacetamide (NAD), and broad-spectrum rooting agents such as ABT and HL-43. Treating the base of cuttings with these auxins increases the rooting rate and also shortens rooting time. In addition, many experiments and production practices have also confirmed that auxin is not the only substance that promotes cutting rooting. Another special substance produced in buds and leaves must also assist before adventitious roots can occur. This substance is the rooting cofactor.

v2. Growth inhibitors Growth inhibitors are substances in plants that hinder rooting. Many studies have confirmed that in the life cycle, old trees have high inhibitor content, and in the annual growth cycle of trees, the dormant period has the highest content. In hardwood cuttings, cuttings near the shoot tip also have higher inhibitor content than cuttings from the base. Therefore, in production practice, corresponding measures can be taken, such as washing with running water, low-temperature treatment, and dark treatment, to eliminate or reduce inhibitors and facilitate rooting.

v3. Nutrients The survival of cuttings has a certain relationship with their internal nutrients, especially the content of carbon and nitrogen and their relative ratio. Generally speaking, a high C/N ratio, that is, high carbohydrate content and relatively low nitrogen compound content in the plant, is more favorable for inducing adventitious roots in cuttings. Low nitrogen can increase the number of roots, while nitrogen deficiency can inhibit rooting. Sufficient nutrition in cuttings can not only promote the formation of root primordia, but also promote the growth of the aboveground part. Practice has proved that supplementing cuttings with carbohydrates and nitrogen can promote rooting. Generally, soaking the lower cut of the cutting in sugar solution or spraying nitrogen such as urea on the cutting can increase the rooting rate. However, exogenous supplementation of carbohydrates can easily cause rotting of the cut.

v4. Plant development Due to the effects of three kinds of aging, namely chronological, ontogenetic, and physiological aging, the rooting ability of plant cuttings also weakens with increasing mother tree age. According to this characteristic, for some rare, precious, or difficult-to-propagate tree species, the following effective approaches can be taken to make them physiologically "rejuvenated."

v(1) Hedge-style scion collection That is, heavily prune the mother trees intended for cutting collection so that they do not grow upward but sprout many new branches.

v(2) Continuous cutting propagation With 2 to 3 consecutive cuttings, the rooting ability of new branches increases sharply, and the rooting rate can increase by 40% to 50%.

v(3) Continuous grafting propagation with juvenile rootstock That is, graft scions collected from old mother trees onto juvenile rootstock, repeatedly and continuously graft 2 to 3 times to "rejuvenate" them, and then collect their branches or needle fascicles for cutting.

v(4) Use basal sprout shoots as cuttings That is, saw off the trunk of an old tree so that the juvenile (young) zone produces new sprout branches for cutting.

v5. Anatomical structure of the stem

The difficulty of cutting rooting is also closely related to the anatomical structure of the stem. If there is a ring-shaped sclerenchyma tissue composed of one, two, or multiple layers of fiber cells in the cortex of the cutting, rooting is difficult; if there is no sclerenchyma tissue in the cortex, or it is discontinuous, rooting is relatively easy. Therefore, during cutting seedling raising, the method of cutting through the cortex can be adopted to destroy the ring-shaped sclerenchyma tissue and promote rooting. For example, the Hubei Forestry Research Institute made longitudinal cuts on olive cuttings, increasing the cutting survival rate.

2. Factors Affecting Cutting Rooting

vIn the process of cutting rooting, the formation of adventitious roots in cuttings is a complex physiological process. Whether a cutting can root and survive after insertion depends not only on the internal factors of the plant itself, but also closely on external environmental factors.

(1) Internal Factors Affecting Cutting Rooting

1. Biological characteristics of tree species Different tree species have different biological characteristics, so their branch rooting ability also differs. According to the difficulty of cutting rooting, they can be divided into:

v(1) Easy-to-root tree species Such as willow, section Tacamahaca, section Aigeiros, dawn redwood, pond cypress, Chinese fir, Japanese cedar, littleleaf box, shrubby sophora, forsythia, Chinese rose, winter jasmine, honeysuckle, ivy, euonymus, nandina, Berberis thunbergii var. atropurpurea, boxwood, Amur honeysuckle, grape, fig, and pomegranate;

v(2) Relatively easy-to-root tree species Such as Chinese arborvitae, Hinoki cypress, false arborvitae, Buddhist pine, black locust, Sophora japonica, tea, camellia, cherry, wild rose, azalea, pearl bush, privet, ash, plane tree, Acanthopanax, elderberry, glossy privet, Kalopanax, Bambusa emeiensis, oleander, and kiwifruit;

v(3) Relatively difficult-to-root tree species Such as golden larch, Chinese juniper, Japanese white pine, Chinese parasol tree, Chinaberry, tree of heaven, date plum, Aglaia, begonia, and jujube;

v(4) Extremely difficult-to-root tree species Such as black pine, masson pine, Japanese red pine, camphor, Chinese chestnut, walnut, oak, tulip tree, persimmon, elm, and maple.

vThe difficulty of rooting among different tree species is only relative. With the deepening of scientific research, some tree species that are very difficult to root may become easy-to-root species for cutting and be promoted and applied in production. Therefore, when raising seedlings by cutting, attention should be paid to referring to proven data. For varieties without data, trial cutting should be carried out to avoid detours. In cutting propagation work, as long as methods are improved, the survival rate can be increased. For example, Japanese red pine and black pine, generally considered very difficult to root by cutting, can reach a rooting rate of over 80% through the cultivation of sprout shoots and hormone treatment under full-light automatic mist cutting seedling technology. Among Chinese rose varieties that are generally easy to root, many excellent lines root with difficulty. For example, if the cutting time is changed to after autumn with leaves, under conditions of heat preservation and mist moisture retention, the rooting rate can reach over 95%. This shows that for many difficult-to-root tree species or flowers, with the continuous progress of science and technology, corresponding measures can be taken according to the genetic characteristics of the parent to find good rooting methods.

v2. Age of cuttings This includes 2 meanings: first, the age of the mother tree from which the branches are collected; second, the age of the collected branches themselves.

v(1) Mother tree age The rooting ability of cuttings decreases with increasing mother tree age. Under general conditions, the older the mother tree, the more difficult it is for plant cuttings to root, while the younger the mother tree, the easier it is to root. This is because the strength of tree metabolism weakens as the developmental stage ages, and its vitality and adaptability also gradually decrease. On the contrary, the young branches of young mother trees have very strong vital activity in the cortical meristem, and the collected branches have a high cutting survival rate. Therefore, when selecting branches, they should be collected from young mother trees. Especially for many difficult-to-root tree species, branches from 1- to 2-year-old seedling-grown plants should be selected, giving the best cutting results. For example, in a cutting experiment by the Hubei Province Qianjiang Forestry Research Institute on one-year-old branches of dawn redwood from different mother tree ages, the cutting rooting rates were: 1-year-old 92%, 2-year-old 66%, 3-year-old 61%, 4-year-old 42%, and 5-year-old 34%. As mother tree age increased, the cutting rooting rate decreased. In addition to the decline in vitality, the reason the rooting ability of cuttings decreases with increasing mother tree age is that the substances necessary for rooting decrease while the substances hindering rooting increase. For example, in the cutting of tree species such as Japanese red pine, black pine, Hinoki cypress, larch, and Japanese cedar, rooting-inhibiting substances or tannins have been found. With increasing age, the nutritional conditions of the mother tree may become worse. Especially in cutting orchards, repeated collection of branches causes soil fertility depletion, and insufficient nutrition in the branches of the mother plant can also affect the rooting ability of cuttings.

v(2) Cutting age The age of the cutting has a significant effect on rooting. Generally, the regenerative capacity of current-year branches is the strongest. This is because young branch cuttings have high endogenous auxin content and vigorous cell meristematic capacity, promoting adventitious root formation. The regenerative capacity of one-year-old branches is also relatively strong, but the specific age also varies by tree species. For example, in poplars, one-year-old branches have a high survival rate, while two-year-old branches have a low survival rate. Even if they survive, the seedlings grow poorly. For dawn redwood and Japanese cedar, one-year-old branches are better, and the base may also carry a short segment of two-year-old branch; while false arborvitae with 2- to 3-year-old branch segments has a high rooting rate.

v3. Attachment position and developmental condition of branches Some tree species have low rooting rates from branches on the canopy, while sprout shoots from the root and trunk base have high rooting rates. This is because the one-year-old sprout shoots at the root collar of the mother tree are at the youngest developmental stage and have strong regenerative capacity. Also, because the sprout shoots grow close to the root system, they obtain more nutrients and have higher plasticity, making them easy to survive after cutting. Although trunk-base sprout branches have a high rooting rate, their sources are few. Therefore, branches used as cuttings are ideally taken from a cutting orchard. If there is no cutting orchard, the seedling stems of cutting seedlings, root-retained seedlings, and root cuttings can be used, among which the latter two are better.

vIn conifers, branches on the main trunk of the mother tree have strong rooting ability, while side branches, especially repeatedly branched side branches, have weak rooting ability. If branches are collected from the canopy, it is better to collect from the lower part of the canopy where light is weaker. In production practice, for some tree species, carrying a portion of two-year-old branch, that is, using the "heel cutting method" or "horse-hoof cutting method," can often increase the survival rate.

Hardwood cuttings must be well developed, thick and strong, fully lignified, and free of pests and diseases.

v4. Different parts of a branch Different parts of the same branch have different numbers of root primordia and amounts of stored nutrients, and their cutting rooting rate, survival rate, and seedling growth amount all show obvious differences. But which part is better specifically also depends on the plant's rooting type and the maturity of the branch. Generally speaking, in evergreen tree species, the middle and upper branches are better. This is mainly because the middle and upper branches grow robustly, have vigorous metabolism and sufficient nutrition, and the new shoots in the middle and upper parts also have strong photosynthesis, which is favorable for rooting. In hardwood cuttings of deciduous tree species, the middle and lower branches are better. This is because the middle and lower branches are well developed and store more nutrients, providing favorable factors for rooting. If deciduous tree species are propagated by softwood cutting, then the middle and upper branches are better. This is because in young branches, the middle and upper parts have the highest endogenous auxin content and vigorous cell meristematic capacity, which is favorable for rooting. For example, in softwood cuttings of white poplar, the shoot tip is best.

v5. Thickness and length of cuttings The thickness and length of cuttings have a certain effect on the survival rate and seedling growth. For the vast majority of tree species, long cuttings have more root primordia and more stored nutrients, which is favorable for cutting rooting. The determination of cutting length should be based on the speed of rooting of the tree species and soil moisture conditions. Generally, hardwood cuttings of deciduous trees are 10 to 25 cm; evergreen tree species are 10 to 35 cm. With the improvement of cutting techniques, cutting has gradually developed toward short cuttings, and some are even cut with one bud and one leaf. For example, tea and grape use 3 to 5 cm short branches for cutting, with very good results.

vFor cuttings of different thicknesses, thick cuttings contain more nutrients, which is favorable for rooting. The suitable thickness of cuttings varies by tree species. Most conifer species are 0.3 to 1 cm in diameter; broadleaf species are 0.5 to 2 cm in diameter.

In production practice, appropriate lengths and thicknesses of cuttings should be used according to need and possibility, and branches should be used rationally, following the principle of cutting thick branches short and leaving thin branches long.

v6. Leaves and buds of cuttings The buds on cuttings are the basis for forming stems and trunks. Buds and leaves can supply the nutrients, growth hormones, vitamins, and other substances necessary for cutting rooting, which is favorable for rooting. This is especially important for softwood cuttings and for the cutting of conifer and evergreen tree species. The number of leaves retained on a cutting is generally determined according to specific conditions, generally 2 to 4 leaves. If there is a misting device to maintain moisture at regular times, more leaves can be retained to accelerate rooting.

vIn addition, branches or cuttings collected from mother trees have significantly reduced resistance to drying and pathogen infection. Therefore, when carrying out cutting propagation, attention must be paid to maintaining the moisture of the cuttings themselves. In production, the lower end of cuttings can be soaked in water, which not only increases the moisture of the cuttings but also reduces rooting-inhibiting substances.

(2) External Factors Affecting Cutting Rooting

The main external factors affecting cuttings rooting are temperature, humidity, aeration, light, and substrate. These factors influence and constrain each other; therefore, during cuttings propagation, all environmental factors must be coordinated to organically meet the various requirements for cuttings rooting, so as to achieve the goal of increasing the rooting rate and cultivating high-quality seedlings.

1. Temperature The suitable temperature for cuttings rooting varies by tree species. The optimal temperature for rooting in most species is 15-25°C, with 20°C being the most suitable. However, many tree species have their own minimum rooting temperature; for example, poplar and willow begin rooting at around 7°C. The general rule is that species that sprout early, such as poplar and willow, require lower temperatures; those that sprout and break dormancy late, as well as evergreen species such as osmanthus, gardenia, and coral tree, require higher temperatures. In addition, plants in different climatic zones have different optimal rooting temperatures; for instance, MaLisch·H of the United States believed that temperate plants are suitable at around 20°C, while tropical plants are suitable at around 23°C. Soviet scholars believed that temperate plants require 20-25°C and tropical plants 25-30°C.

Different tree species also have different soil temperature requirements for cuttings rooting. Generally, when soil temperature is 3-5°C higher than air temperature, it is extremely favorable for rooting. This promotes the formation of adventitious roots while being unsuitable for bud sprouting, concentrating nutrients so that buds sprout and grow only after adventitious roots have formed. In production, horse manure or electric heating wires can be used as fermentation materials to raise ground temperature, and solar heat energy can also be used for inverted cutting to promote rooting, thereby increasing the survival rate of cuttings.

Temperature is even more important for softwood cuttings. Below 30°C is favorable for the utilization of rooting-promoting substances within the branches, thus benefiting rooting. However, temperatures above 30°C will lead to cutting failure. Generally, misting methods can be used to lower the temperature of cuttings. The optimal period for cutting activity is also the period when pathogens are rampant, so special attention should be paid during cuttings propagation.

2. Humidity During the rooting process of cuttings, the relative humidity of the air, the humidity of the cutting medium, and the water content of the cuttings themselves are key to cutting survival, especially for softwood cuttings, where maintaining appropriate humidity requires particular attention.

(1) Relative humidity of the air The relative humidity of the air has a great influence on difficult-to-root coniferous and broadleaf tree species. The relative humidity required by cuttings is generally around 90%. Hardwood cuttings can tolerate slightly lower levels, but for softwood cuttings the relative humidity must be controlled above 90% to minimize transpiration intensity of the branches. In production, methods such as misting and interval-controlled spraying can be used to increase the relative humidity of the air, making it easier for cuttings to root.

(2) Cutting medium humidity Cuttings most easily lose water balance, so the cutting medium must have suitable moisture. The humidity of the cutting medium depends on the cutting substrate, cutting material, and management techniques. According to cutting experiments with Populus tomentosa, the water content in the cutting medium is generally suitable at 20%-25%. When the water content is below 20%, both rooting and survival of cuttings are affected. Reports indicate that from cutting to callus formation and rooting, cuttings have different water content requirements at each stage, generally higher at the former stage and decreasing successively at later stages. Especially after complete rooting, water supply should be gradually reduced to inhibit vigorous growth of the above-ground parts of cuttings, increase the lignification degree of new shoots, and better adapt to the field environment after transplanting.

3. Aeration conditions Cuttings need oxygen during rooting. Fujii of Japan conducted experiments with grapes in cutting media with different oxygen concentrations (Table 5-1). From Table 5-1, it can be seen that the rooting rate of cuttings is proportional to the oxygen content in the cutting medium. Therefore, during cuttings propagation, the cutting substrate should be loose and well-aerated. Especially for tree species with high oxygen demand, it is even more important to choose a loose and well-aerated cutting substrate and to insert shallowly. If the substrate is loam, the soil must be loosened promptly after each irrigation, otherwise the survival rate will decrease.

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4. Light Light can promote cuttings rooting and is indispensable for evergreen trees and softwood cuttings. However, during the cutting process, intense light can cause cuttings to dry out or become scorched, reducing the survival rate. In practice, measures such as misting to cool down or appropriate shading can be taken to maintain the water balance of cuttings. When cutting in summer, the best method is to use the full-light automatic intermittent misting method, which ensures water supply without affecting light.

5. Cutting substrate Regardless of the type of substrate used, as long as it can meet the water and aeration requirements of cuttings for the substrate, it is beneficial for rooting. Currently, the cutting substrates used fall into the following three states:

(1) Solid state The most commonly used substrate in production, generally including river sand, vermiculite, perlite, furnace slag, peat soil, carbonized rice husk, peanut shells, moss, foam plastic, etc. These substrates have good aeration and drainage performance. However, after repeated use, the particles often break down and the powder content increases, so the substrate should be replaced with new material periodically.

(2) Liquid state Inserting cuttings into water or nutrient solution to root and survive is called liquid cutting. Liquid cutting is often used for easily rooted tree species. Since nutrient solution is used as the substrate, cuttings are prone to rot, so it should generally be used with caution.

(3) Gaseous state Creating a water vapor mist state in the air and suspending cuttings in the mist to root and survive is called mist cutting or aerial cutting. Mist cutting, as long as temperature and air relative humidity are well controlled, can fully utilize space, root cuttings quickly, and shorten the nursery cycle. However, since cuttings root under conditions of high temperature and high humidity, hardening off becomes one of the important steps for mist cutting survival.

The selection of substrate should be based on the requirements of the tree species, choosing the most suitable substrate. When cutting in the open field, it is practically impossible to replace the cutting soil over a large area, so sandy loam with good drainage is usually chosen.

III. Techniques for Promoting Cuttings Rooting

1. Treatment with auxins and rooting promoters

(1) Growth hormone treatment Commonly used auxins include naphthaleneacetic acid (NAA), indoleacetic acid (IAA), indolebutyric acid (IBA), 2,4-D, etc. The methods of use are as follows: first, dissolve the auxin in a small amount of alcohol, then prepare solutions of different concentrations. Low concentrations (such as 50-200 mg/L) are used to soak the lower end of cuttings for 6-24 h, while high concentrations (such as 500-10000 mg/L) can be used for quick treatment (a few seconds to one minute); second, mix the dissolved auxin uniformly with talc powder or charcoal powder, dry in the shade, and make into powder, then dip the wet lower end of cuttings into the powder before inserting; or dilute the powder with water to make a paste and dip the lower end of cuttings; or make into a mud-like consistency and embed the lower end of cuttings. The treatment time and solution concentration vary depending on the tree species and type of cutting. Generally, difficult-to-root species require higher concentrations, while easy-to-root species require lower concentrations. Hardwood cuttings require higher concentrations, while softwood cuttings require lower concentrations.

(2) Rooting promoter treatment Currently, widely used products include the "ABT Rooting Powder" series developed by Wang Tao of the Research Institute of Forestry, Chinese Academy of Forestry; the broad-spectrum "Plant Rooting Agent HL-43" developed by the Department of Forestry, Huazhong Agricultural University; "Genbao" developed by the Department of Forestry, Shanxi Agricultural University, which won the National Science and Technology Invention Award; and the "3A Series Root-Promoting Powder" developed by the Kunming Institute of Landscape Architecture, etc. They can all increase the rooting rate of many trees such as ginkgo, osmanthus, Chinese chestnut, red maple, cherry blossom, plum, larch, etc., with rooting rates reaching over 90%, and well-developed root systems with an increased number of absorbing roots.

2. Washing and elution treatment Washing and elution treatments generally include warm water treatment, running water treatment, alcohol treatment, etc. Washing treatment can not only reduce the content of inhibitory substances in branches but also increase the water content in branches.

(1) Warm water washing treatment Place the lower end of cuttings in warm water at 30-35°C and soak for several hours or longer, with the specific time varying by tree species. Some coniferous branches such as pine, larch, and spruce are soaked for 2 h, which serves a degreasing function and is beneficial for wound healing and rooting.

(2) Running water washing treatment Place cuttings in flowing water and soak for several hours, with the specific time also varying by tree species. Most are within 24 h, some can reach 72 h, and some even longer.

(3) Alcohol washing treatment Treatment with alcohol can also effectively reduce inhibitory substances in cuttings and greatly increase the rooting rate. The concentration generally used is 1%-3%, or a mixture of 1% alcohol and 1% ether, with a soaking time of about 6 h, as for rhododendrons.

3. Nutrient treatment Treating cuttings with vitamins, sugars, and other nitrogen substances is also one of the measures to promote rooting. For example, treating cuttings of cedar, Chinese juniper, dawn redwood, and other species with 5%-10% sucrose solution for 12-24 h has a very significant effect on promoting rooting. If sugars are used together with plant auxins, the effect is even better. When doing softwood cuttings, spraying urea on the leaves is also a type of nutrient treatment.

4. Chemical agent treatment Some chemical agents can also effectively promote cuttings rooting, such as acetic acid, phosphoric acid, potassium permanganate, manganese sulfate, magnesium sulfate, etc. For example, in production, soaking cuttings of Euonymus and lilac in 0.1% acetic acid aqueous solution can significantly promote rooting. Soaking cuttings in 0.05%-0.1% potassium permanganate solution for 12 h can not only promote rooting but also inhibit bacterial development, serving a disinfecting function.

6. Heating treatment In spring, because air temperature is higher than ground temperature, cuttings in the open field tend to sprout and leaf out before rooting, thereby reducing the cutting survival rate. To address this, measures such as laying electric heating wires in the cutting bed (i.e., electric heating hotbed method) or placing fresh horse manure in the cutting bed (i.e., fermentation material rooting promotion method) can be used to raise ground temperature and promote rooting.

7. Inverted cutting for rooting promotion This is generally done in late winter and early spring. Taking advantage of the characteristic that spring surface temperature is higher than the temperature inside the pit, cuttings are placed upside down in the pit, filled with sand to fill the gaps, and covered with 2 cm of sand on the pit surface, so that the temperature at the base of the inverted cuttings is higher than at the tip. This creates favorable conditions for the formation of root primordia from callus tissue at the base of cuttings, thereby promoting rooting, but attention must be paid to water control.

8. Etiolation treatment Before the growing season, cover the branches intended for cuttings with black plastic bags, allowing them to grow under dark conditions and form younger, more tender tissues. After the branches and leaves have grown to a certain extent, cut them off for cuttings, which can create more favorable conditions for rooting.

9. Mechanical treatment During the tree growing season, girdle, notch, or bind the base of branches with wire, hemp rope, or nylon rope to prevent carbohydrates and auxins from being transported downward from the upper part of the branches, allowing them to store nutrients. Then during the dormant period, cut the branches from the base for cuttings, which can significantly promote rooting.

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IV. Cutting Timing, Selection and Trimming of Cuttings

(I) Cutting Timing

Generally speaking, plant cutting propagation can be carried out in all four seasons. The suitable cutting time varies depending on the plant species and characteristics, cutting methods, etc.

1. Spring cuttings Suitable for most plants. Spring cutting uses dormant branches from the previous year directly or after winter low-temperature storage for cuttings, also known as hardwood cuttings. The rooting inhibitory substances in the branches have already been transformed, and nutrients are abundant, but under the same conditions, it is easy for the above-ground and underground parts to develop out of sync, causing metabolic disorders in the branches. Therefore, spring cuttings should be done early, and conditions should be created to first break the dormancy of the lower part of the branches while keeping the upper part dormant, so that buds sprout and grow only after adventitious roots have formed. Thus, the key technical point for cutting propagation in this season is to take measures to raise ground temperature. The methods used in spring cutting production include open-field cutting and plastic low-tunnel protected cutting.

2. Summer cuttings Summer cutting uses vigorously growing softwood or semi-lignified branches of the current year for cuttings, also known as softwood cuttings. Generally, coniferous trees use semi-lignified branches, and broadleaf trees use softwood from the period of most vigorous height growth. Summer cutting branches are in a period of vigorous growth, with strong cell division ability, vigorous metabolism, and high endogenous auxin content in the branches; these factors are all conducive to rooting. However, in summer, due to high temperatures and tender branches, it is easy for branches to lose water through transpiration and die. Therefore, the key technical point for summer cutting propagation is to increase the relative humidity of the air, reduce the transpiration intensity of cutting leaves, and increase the survival rate of detached branches and leaves, thereby increasing the rooting survival rate. Methods commonly used for summer cuttings include plastic low-tunnel cutting under shade frames and full-light automatic intermittent misting cutting.

3. Autumn cuttings Autumn cutting uses branches that are well-developed, rich in nutrients, and have stopped growing but have not yet entered dormancy. The inhibitory substance content in the branches has not reached its peak, which can promote earlier callus formation and is beneficial for rooting. Autumn cuttings should be done early to facilitate complete material transformation and safe overwintering. Therefore, the key technical point for cutting propagation in this season is to take measures to raise ground temperature. Methods commonly used for autumn cuttings include plastic low-tunnel protected cutting propagation, and in the north, sunken hotbeds can also be used for cutting propagation.

4. Winter cuttings Winter cutting uses dormant branches that have had their dormancy broken for hotbed cuttings. In the north, it should be done in plastic tunnels or greenhouses, with electric heating wires laid on the substrate to raise the temperature of the cutting substrate. In the south, cuttings can be done directly in the nursery field.

Different regions can choose different periods for different tree species. For deciduous trees, cuttings can be done in both spring and autumn. However, spring is more common, and spring cuttings should be done early before buds sprout. In the north, it can be done when the soil begins to thaw, generally from mid-to-late March to mid-to-late April. Autumn cuttings should be done before the soil freezes, inserting as soon as branches are collected. In the warm regions of southern China, autumn cuttings are commonly used. In the arid and cold northern regions or areas with little snow in winter, cuttings are prone to wind drying and frost damage during autumn cutting, so after cutting they should be covered with soil, and the soil should be removed when buds sprout in spring. To solve the difficulties of autumn cutting and reduce overwintering work such as soil covering, cuttings can be stored until the following spring for cutting, which is extremely safe. Growing-season cuttings of deciduous trees are mostly done during the stable period after the first growth phase of summer ends. Production practice has proven that in many regions and for many tree species, cuttings can be done in all four seasons. For example, roses, wild roses, pomegranate, gardenia, Hypericum, and conifers such as pines and cypresses can all be cut in all four seasons in Hangzhou.

Cuttings of evergreen tree species in the south are mostly done during the plum rain season. Generally, evergreen trees require higher temperatures for rooting, so cuttings of evergreen trees should be taken after the first growth phase ends and before the second growth phase begins. This coincides with the plum rain season in the south from May to July, when there is plenty of rain and high humidity, making it difficult for cuttings to wither and easy for them to survive.

Cuttings are divided into dormant-period and growing-period types based on the time of collection; the former are hardwood cuttings, and the latter are soft (green) cuttings.

1. Selection and Trimming of Hardwood Cuttings

(1) Time for collecting cuttings The stored nutrients in cuttings are the main energy source for hardwood cuttings to root and sprout. The amount of stored nutrients varies with the time of collection, so collection should be done during the period when branches contain the most nutrients. This period is when sap flow is slow and growth has completely stopped, i.e., for deciduous tree species, after leaf fall in autumn or from the beginning of leaf fall to before sprouting the following spring.

(2) Selection of cuttings According to the principles of cutting survival, one should select well-developed, fully lignified 1-2 year old branches or sprout shoots from superior young mother trees; select healthy, pest-free, thick and strong branches with high nutrient content.

(3) Storage of branches In northern regions, if cuttings are not inserted immediately after collection, they are stored until the following spring for cutting. The methods include open-field burial and indoor storage. Open-field burial involves selecting a high, dry, well-drained, wind-sheltered, sun-facing location and digging a trench, generally 50-60 cm deep (depending on local climate, but the depth must be below the frost line). Bundle branches in groups of 50-100, stand them upright at the bottom of the trench, cover well with wet sand, and place a straw bundle upright in the middle for ventilation. Check 1-2 times per month to maintain suitable temperature and humidity conditions and ensure safe overwintering. After burial, the bark softens, and stored substances inside begin to transform, laying a good foundation for spring cuttings rooting. Indoor storage also involves burying branches in wet sand, paying attention to indoor ventilation and maintaining appropriate temperature. The stacking layers should not be too high, preferably 2-3 layers; too high will cause high temperatures and branch rot. In the south, if there are few cuttings that need storage, they can be placed in the storage compartment of a refrigerator. In landscaping practice, branches removed during pruning and shaping can also be selected and stored for future use.

(4) Trimming of cuttings Generally, long cuttings are 15-20 cm long, ensuring 2-3 well-developed buds on the cutting; single-bud cuttings are 3-5 cm long. When cutting, the upper cut should be about 1 cm from the terminal bud. The position of the lower cut varies by plant species. Generally, near the node there are many parenchyma cells, rapid cell division, and rich nutrients, making it easy to form callus and roots, so the lower cut of cuttings should be close below the node. Lower cuts include flat cut, slant cut, double cut, heel cut, and several others (see Figure 5-1). Generally, flat cuts produce roots distributed evenly in a ring shape and facilitate mechanized cutting; for species that root from the bark and root quickly, flat cuts should be used. Slant cuts have a larger contact area with the cutting substrate, can form a larger callus area, facilitate water and nutrient absorption, and improve survival rate, but roots mostly grow at one end of the slant cut, easily forming biased roots, and cutting is also more labor-intensive. Double cuts have an even larger contact area with the cutting medium and are used more on difficult-to-root plants. Heel cuts are generally used when the lower end of the cutting carries 2-3 year old branch segments, commonly used for coniferous trees.

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Figure 5-1 Lower cut shapes of cuttings and rooting

1. Flat cut 2. Slant cut 3. Double cut 4. Flat lower cut with even rooting 5. Slant lower cut with roots biased to one side

2. Selection and Trimming of Softwood Cuttings

(1) Time for collecting softwood cuttings Softwood cuttings are inserted as soon as collected. It is best to select from vigorously growing young mother trees, and preferably use softwood that has begun to lignify, as it contains sufficient nutrients, has strong vitality, and easily calluses and roots. However, branches that are too tender or too lignified are not suitable. Softwood cuttings should be collected in the early morning before sunrise or on cloudy and rainy days; do not collect under sunlight, in wind, or when the weather is very hot.

(2) Selection of softwood cuttings Generally, for coniferous trees such as pine, cypress, and juniper, it is better to take semi-lignified branches from the middle and upper parts in late summer for cuttings. Practical experience has proven that using middle and upper branches for cuttings results in better rooting than basal branches in most cases. Coniferous trees are not very demanding regarding moisture, but attention should be paid to maintaining branch moisture. For softwood cuttings of deciduous broadleaf trees and evergreen broadleaf trees, young branches are generally taken during the period of most vigorous height growth for cuttings. For large-leaved plants, it is best to collect branches when the leaves have not yet expanded into large leaves. After collecting, spray water promptly and pay attention to moisture retention. For softwood cuttings, pre-treatment of branches before insertion is very important. Plants with high tannin content and difficult-to-root species can be treated with etiolation, girdling, binding, etc., before the growing season.

(3) Trimming of softwood cuttings After the branches are brought back, trim them in a cool, wind-sheltered place. Generally, cuttings are 10-15 cm long with 2-3 buds. The number of leaves retained on the cutting can be determined according to plant species and cutting method. The lower cut should be made as a flat cut or a small slant cut to reduce cut rot.

V. Types and Methods of Cuttings

In plant cutting propagation, according to the different materials used for propagation, it can be divided into stem cuttings, root cuttings, leaf cuttings, bud cuttings, fruit cuttings, etc. The classification is shown in Figure 5-2.

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(I) Stem Cuttings

Stem cuttings are the most widely used cutting method for landscape trees. According to branch maturity and cutting season, stem cuttings can be further divided into dormant branch cuttings and growing branch cuttings. Various stem cuttings are distinguished by the morphology and length of the materials used.

1. Dormant branch cuttings Dormant branch cuttings use branches that have already become dormant as cuttings. Since dormant branches are already lignified, they are also called hardwood cuttings. They are usually divided into long cuttings and single-bud cuttings. Long cuttings use two or more buds for cutting, while single-bud cuttings use a branch segment with one bud; because the branch is shorter, it is also called short cuttings.

(1) Long cuttings Generally include ordinary cuttings, heel cuttings, mallet cuttings, etc. (see Figure 5-3).

① Ordinary cutting This is the most widely used method in woody plant cutting propagation, and most tree species can use this method. It can be done in cutting beds or in the open field, such as flat planting or ridge planting. Generally, the cutting length is 10-20 cm, with 2-3 buds retained on the cutting. Insert the cutting into soil or substrate to a depth of 2/3 of the cutting length. Cuttings that are shorter should be inserted vertically, which avoids biased roots caused by slant insertion and facilitates lifting of seedlings.

② Heel cutting The base of the cutting carries a portion of two-year-old branch, shaped like a heel. This type of cutting has concentrated nutrients at the lower part and roots easily, but wastes branches, as only one cutting can be taken from each branch. It is suitable for difficult-to-root species such as pines, cypresses, and osmanthus.

③ Mallet cutting This is a type of heel cutting where the old branch portion carried at the base is larger than in heel cuttings, generally 2-4 cm long, with both ends cut at a slant to form a mallet shape.

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Figure 5-3 Cutting collection and hardwood cuttings

1. Heel cutting 2, 3. Mallet cutting

In addition to the above three cutting methods, to improve the rooting survival rate, several cutting methods have been developed based on ordinary cutting with various measures:

Split cutting The lower part of the cutting is split from the middle and a stone or similar is inserted. This uses artificial wounding to stimulate callus tissue production and expand the rooting area of the cutting. This method is mostly used for difficult-to-root tree species that root through callus tissue, such as osmanthus, camellia, and plum blossom.

Soil ball cutting The base of the cutting is wrapped in a ball of relatively heavy clay soil, and then the cutting together with the soil ball is inserted into the soil, using the soil ball to retain higher moisture. This method is mostly used for evergreen trees and coniferous trees, such as cedar and bamboo-leaf pine.

Tumor cutting In this method, during the growing season before the branch is cut from the tree, wounding, girdling, and other methods are used to cause the base of the cutting to form tumor-like protrusions of callus tissue, increasing nutrient storage, and then it is cut off for insertion. This method involves many steps and wastes branches. However, it is beneficial for propagating difficult-to-root tree species, so it is mostly used for propagating precious tree species.

Long trunk cutting This uses long branches for cuttings, generally 50 cm long, or even 1-2 m long 1-year to multi-year-old branches or trunks as cuttings. It is mostly used for easily rooted tree species. This method can produce large seedlings with a main trunk in a short time, or they can be inserted directly where they are to be planted, reducing transplanting.

Floating water cutting This method uses water as the cutting substrate, i.e., inserting cuttings into water and planting them promptly after rooting. Roots from water cuttings are relatively brittle and easily broken if too long.

(2) Single-bud cuttings (short cuttings) Using branches with only one bud for cuttings, the selected branches are short, generally less than 10 cm, saving material, but the cuttings have fewer nutrients and lose water easily. Therefore, the lower cut is made at a slant to expand the water-absorbing area and callus surface of the branch cut, which is beneficial for rooting, and misting is needed to maintain relatively high air humidity and temperature so that cuttings can root and survive in a short time. This method is mostly used for cutting propagation of evergreen tree species. When using this method to cut white camellia, branches of about 2.5 cm take 2-3 months to root, with a survival rate of up to 90%; the survival rate for osmanthus cuttings reaches 70%-80%.

Before dormant branch cuttings, the cutting bed should be prepared. Open-field cuttings require careful soil preparation and sufficient base fertilizer to make the soil loose and moisture-sufficient. If necessary, the cutting medium should be disinfected. Cutting density can be determined according to tree growth rate, seedling specifications, soil conditions, and equipment used. Generally, plant spacing is 10-50 cm and row spacing is 30-80 cm. In greenhouses and propagation rooms, dense cutting is generally used, and after cuttings root and sprout, they are transplanted. The insertion angle of cuttings includes vertical insertion and slant insertion; under general conditions, vertical insertion is mostly used. The angle for slant insertion should not exceed 45o. Insertion depth should be determined according to tree species and environment. For deciduous tree species, cuttings are inserted entirely into the ground, with one bud exposed above or level with the ground. For open-field cuttings in warm, humid southern regions, buds can be slightly exposed. In greenhouses and propagation rooms, the upper end of cuttings is generally exposed above the cutting substrate. For evergreen tree species, the insertion depth should be 1/3-1/2 of the cutting length.

2. Growing branch cuttings During the growing season, using vigorously growing young branches or semi-lignified branches as cuttings for propagation. Softwood has many parenchyma cells, strong cell vitality, and strong meristematic ability; moreover, softwood has high water content, more soluble nutrients, strong enzyme activity, and new leaves can produce some photosynthetic products. These are all internal factors favorable for rooting, and many tree species are suitable for softwood cutting. Cutting length is generally shorter than hardwood cuttings, mostly with 1-4 internodes, about 5-20 cm long, retaining some leaves, with larger leaves cut in half. The lower cut is located below the leaf and axillary bud to facilitate rooting; the cut can be flat or slant. Then insert into the cutting medium (see Figure 5-4).

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Figure 5-4 Common softwood cutting methods

For growing branch cutting timing, in the south it can be done in spring, summer, and autumn, while in the north it is mainly done in summer. The specific cutting time is in the morning and evening, inserting as soon as collected, mostly on cutting beds that are loose, well-aerated, and have good moisture retention. The insertion depth is about 3 cm, and the density should be such that the leaves of adjacent cuttings do not overlap, so as to maintain sufficient photosynthesis. The insertion angle is generally vertical. The insertion depth is generally 1/2-1/3 of the cutting length; if environmental conditions can be artificially controlled, the shallower the insertion depth the better, about 0.5 cm, as long as it does not fall over. Growing branch cuttings require high air humidity to avoid excessive water transpiration from the plant. Currently, full-light automatic intermittent misting cutting equipment, plastic low-tunnel cutting under shade frames, and methods such as dense cutting in large pots and water cutting are mostly used (see Figure 5-5) to ensure suitable air humidity. This type of cutting has a relatively high cutting density on the bed, and they are mostly transplanted to the nursery field immediately after rooting.

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Figure 5-5 Softwood cutting methods

1. Plastic tunnel cutting 2. Dense cutting in large pots 3. Dark bottle water cutting

(II) Root Cuttings

For some tree species that are difficult to root from stem cuttings, root cuttings can be used for asexual propagation to maintain the superior traits of the mother plant.

1. Root collection Generally, robust young trees or vigorously growing 1-2 year old seedlings should be selected as mother trees for root collection, and the root cuttings are best one year old. If collecting roots from a single tree, do not collect too many at one time, otherwise it will affect the growth of the mother tree. Do not damage the root bark when collecting. Root collection is generally done during the tree dormant period, and after collection, they should be buried promptly for storage. In the south, it is best to collect roots in early spring and insert them immediately.

2. Trimming of root cuttings Depending on the tree species, root cuttings can be cut into different specifications. Generally, root cuttings are 15-20 cm long, with the thick end 0.5-2 cm in diameter. To distinguish the upper and lower ends of root cuttings, the upper end can be cut flat and the lower end cut at a slant. In addition, some tree species such as Chinese toon, black locust, and paulownia can also use thin short root segments, 3-5 cm long and 0.2-0.5 cm thick.

3. Insertion Before cutting, carefully level the cutting medium and water thoroughly. Insert root cuttings about 15-20 cm long vertically or at a slant into the soil, paying attention to the upper and lower ends of the roots and not inserting them upside down. After insertion until sprouting and rooting, it is best not to irrigate, to avoid lowering ground temperature and causing root cutting rot due to excessive water. For some tree species, thin short root segments can also be propagated by sowing.

(III) Leaf Cuttings

Using leaves for propagation to cultivate new plants works because leaves have regeneration and callus-forming ability. For most woody plants, the above-ground part of leaf cuttings develops from bud primordia. Therefore, leaf cuttings should carry bud primordia and protect them from damage, otherwise the above-ground part cannot form. The underground part (roots) is induced from root primordia at the callus site and develops into roots. Leaf cuttings of woody plants mainly include needle-bundle water cutting propagation (for full-leaf cuttings and partial-leaf cuttings of herbaceous flowers and foliage herbaceous plants, refer to relevant floriculture textbooks). For example, the Forestry Research Institute of Jingzhou Prefecture, Hubei Province, successfully researched full-light misting water cutting propagation of slash pine, loblolly pine, Masson pine, etc., and applied it in production; the Rushan County Nursery and Yantai Forestry Research Institute of Shandong successively cultivated needle-bundle seedlings of Japanese black pine and Japanese red pine by water cutting. The procedure for needle-bundle propagation is:

1. Leaf collection In autumn and winter, select robust 2-year-old seedlings or current-year thick needle bundles from young branches as propagation material.

2. Needle bundle treatment Wash the collected needle bundles, then store the bundles in disinfected pure sand (burying 2/3 of the bundle is sufficient), water thoroughly, keep moist frequently, and control the temperature between 0-10°C for about one month. Sand storage serves a degreasing function. After sand storage, use a sharp blade to cut off the base of the bundle below the growth point (do not damage the growth point), creating a fresh wound that is beneficial for callusing and rooting. The cut bundles are then treated with hormones.

3. Water cutting Water cutting is actually not inserting into water but into a certain nutrient solution. The basic formula of the nutrient solution is boric acid 50-70 mg/L, ammonium nitrate 20 mg/L, vitamin B1 20 mg/L; other chemicals such as vitamin B6 can also be added according to different tree species. Well water can be used for the nutrient solution, with a pH below 7. Insert the needle bundles that have been cut and hormone-treated into the hydroponic nutrient solution and fix them in place. Control the temperature between 10-28°C, air relative humidity at around 80%, and when accumulated temperature reaches about 1000°C, rooting accelerates. Generally, about once a week, rinse the bundles, clean the hydroponic container, and replace the nutrient solution.

4. Transplanting When the bundle roots grow to 1-2 cm, they can be transplanted, and mycorrhizae should be inoculated at the same time. When transplanting, use a small shovel to make a hole, insert the rooted bundle, with depth just enough to cover the roots, press gently, and keep the soil moist frequently. In the early stage after transplanting, when the sun is too strong around noon, appropriate shading is needed. The most critical issue after transplanting is to promote the sprouting of the growth point, germination, and stem growth. Bundle germination is closely related to bundle quality. Robust, heavy bundles germinate easily. In addition, inoculating mycorrhizae has a promoting effect on germination. Sometimes, to promote germination, gibberellin, etc., can also be sprayed.

After bundle seedlings grow new roots, germinate, and produce stems, the management is the same as general seedling propagation methods.

Post-cutting management is also very important. Generally, immediately after cutting, irrigate thoroughly once, then pay attention to frequently maintaining the humidity of the cutting medium and air, and do a good job of moisture conservation and soil loosening. If cuttings carry flower buds, they should be removed early. If the above-ground part has already unfolded leaves before rooting, some leaves should be removed. When new shoots grow to 15-30 cm, one robust upright branch should be selected and retained, and the rest removed. If necessary, grass can be spread between rows to maintain moisture and prevent rainwater from splashing mud onto tender leaves. For hardwood cuttings of difficult-to-root tree species, rooting takes a long time, and attention should be paid to shading when necessary. Softwood open-field cuttings also need shade frames for shading and cooling, from after 10 a.m. to before 4 p.m. each day, while misting daily to maintain humidity. When using sealed plastic tunnel cutting, the number of irrigations can be reduced to 1-2 times per week, but the temperature and humidity inside the tunnel must be adjusted promptly. After cuttings survive, they must go through a hardening-off stage to gradually adapt to the external environment before being moved to the nursery field. When cutting in greenhouses or hotbeds, after rooting and leaf unfolding, windows should be gradually opened for air circulation to gradually adapt to the external environment, and then they can be moved to the nursery field.

In areas with higher air temperature and sufficient sunlight, full-light intermittent misting cutting beds can be used for cuttings.

VII. New Techniques for Cutting Propagation

(I) Full-Light Automatic Misting Technology

1. Origin of full-light automatic misting cuttings During the long rooting process of cuttings, whether the cuttings can root and survive depends most importantly on keeping the branches from losing water. If the branches lose water, there is no hope of rooting. All measures taken during the cutting process are aimed at maintaining branch moisture, creating conditions for branches detached from the mother plant to avoid water loss while still being able to obtain the water needed for branch life activities, as well as other nutrients and environmental conditions suitable for rooting.

As early as 1941, Raines, Kadel, and Fischer of the United States simultaneously reported that misting technology could keep branches from losing water and also promoted the rooting effect of cuttings. Hess and Snyder proposed using clock-controlled misting devices. Langhen and Peterson invented the use of sunlight control. Preston proposed the air humidification method. In the 1960s, Cornell University in the United States invented an intermittent misting device controlled by electronic leaves and proved that its effect and economic benefits were superior to the previous three, which brought mist cutting spray devices into the stage of production application. In 1977, domestic reports began and this new technology was introduced. In China, in the early 1980s, Tan Yong of Nanjing Forestry University first reported the development of the "electronic leaf" intermittent misting device and its successful application in seedling propagation. The Hunan Forestry Research Institute and other units successively developed improved "electronic leaf" and "electronic seedling" devices. The Beijing Municipal Bureau of Parks and the Beijing Botanical Garden of the Chinese Academy of Sciences also successively developed "electronic leaf" intermittent misting devices. In 1983, Xu Chuansen of the Jilin Railway Branch developed a sensor based on the dry-wet bulb hygrometer principle and a complete set of misting devices, which were promoted to many seedling propagation units nationwide. In 1987, the Science and Technology Information Center of the Ministry of Forestry developed the 2P-204 automatic intermittent misting device's moisture evaporation controller, which was also promoted nationwide. In just over ten years, full-light mist cutting spread to many seedling propagation units nationwide. In 1995, the Chinese Academy of Forestry also introduced a rotary full-light mist cutting device, greatly increasing the control area of the propagation bed and producing very good propagation results and economic benefits.

2. Full-light automatic misting device

(1) Humidity controller Receives and amplifies signals input by the electronic leaf or sensor, controls relay opening and closing; the relay opening and closing is synchronized with the solenoid valve, thereby controlling whether misting occurs. The humidity controller contains a signal amplification circuit and a relay.

(2) Electronic leaf and humidity sensor The electronic leaf and humidity sensor are signal-generating devices. The electronic leaf has two poles of a low-voltage power source installed on an insulating board; the two poles are connected to the humidity controller by wires, forming a closed circuit. The humidity sensor uses changes in the dry-wet bulb temperature difference to generate signals, which are input to the humidity controller, thereby controlling misting.

(3) Solenoid valve The solenoid valve is an electromagnetic water valve switch that controls the water switch. When the solenoid valve receives the electrical signal from the humidity controller, the solenoid valve opens and the nozzle sprays water. When there is no electrical signal, the solenoid valve closes and no water is sprayed.

  (4) High-pressure water source The pressure requirement of the water source for full-light automatic misting is 1.5-3 Kg/cm, and the water supply volume must match the nozzle spray volume, with uninterrupted water supply. Below this water pressure and flow rate, the sprayed water cannot be atomized; sufficient pressure and flow rate are necessary. The full-light automatic misting device is shown in Figure 5-6.

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Figure 5-6 Full-light automatic misting device diagram

1. Electronic leaf 2. Solenoid valve 3. Humidity controller 4. Nozzle 5. Cutting bed

3. Working principle Whether the nozzle can spray depends first on the electrical signal input by the electronic leaf or humidity sensor. The electronic leaf and humidity sensor have two electrodes. When there is water on the electronic leaf, the closed circuit of the electronic leaf or humidity sensor is connected, and an induction signal is input. The weak electrical signal is amplified step by step through the wireless circuit signal. The amplified electrical signal is first input to a small relay, and the small relay then drives a large relay. When the large relay is energized, it pulls the solenoid valve switch into the closed state. When the water film on the electronic leaf evaporates dry, the induction circuit is in the open state, and no induction signal is input to the small relay and large relay. The large relay is not energized and cannot pull down the solenoid valve switch; the solenoid valve switch is in the open state, the solenoid valve opens, and the nozzle sprays water. When the water mist reaches a certain level, it again connects the closed circuit of the electronic leaf, an induction signal is input, and through the above signal amplification, the relay linkage pulls the solenoid valve switch closed. This cycle repeats continuously.

4. Precautions for full-light automatic misting cuttings The substrate for full-light automatic misting cuttings must be loose, well-aerated, and well-drained, preventing water accumulation in the bed that would cause branch rot, while still keeping the cutting bed moist.

For full-light automatic misting cuttings, generally speaking, the more leaves the cutting carries and the longer the cutting, the higher the rooting rate; larger cuttings produce more robust seedlings after survival. However, cuttings that are too long waste cutting material and are uneconomical to use. Therefore, about 15 cm is generally suitable. Conversely, branches with few and short leaves have low survival rates, poor seedling quality, and low transplant survival rates. Leaves and small branches on the lower part of the cutting that would be inserted into the substrate should be cut off.

If rooting hormones are used in full-light automatic misting cuttings, they can further promote cuttings rooting. Especially for difficult-to-root tree species, hormone treatment can increase the rooting rate, advance rooting, and increase root quantity. Automatic misting cuttings easily cause nutrient leaching from branches because the frequent washing effect also leaches hormones from the branches. Using hormone treatment can increase branch nutrients and advance rooting, so using misting cuttings combined with hormone treatment is even more important.

(II) Substrate Electric Heating Hotbed Rooting Promotion Propagation Technology

Electric heating hotbed propagation technology is designed by utilizing the temperature difference effect of plant rooting to create the optimal temperature for plant callusing and rooting. Using electric heating wires to increase the seedbed ground temperature and promote cuttings rooting is a modern propagation method. Because it uses electric heating, the target temperature can be manually controlled through a plant growth simulation computer, and temperature stability can be maintained, which is beneficial for cuttings rooting. It has been widely applied in ornamental tree cuttings, forest tree cuttings, fruit tree cuttings, vegetable seedling propagation, and other fields. First, select a relatively high and dry flat area indoors or in a greenhouse. Use bricks to build a seedbed 1.5 m wide along the edge, and lay a layer of yellow sand or perlite on the bottom. Place one 7 cm x 7 cm square wooden strip at each end and in the middle of the bed, then nail small iron nails every 6 cm on the wooden strips, with the nail depth being 1/2 of the nail length. The electric heating wire is wound between the small iron nails. The two ends of the electric heating wire are led out of the hotbed and connected to the propagation controller. Then cover the electric heating wire with wet sand or perlite, arrange the cutting bases downward in the hotbed, and fill wet sand (or perlite) between cuttings until the tops of the cuttings are covered. Insert a temperature sensing probe into the seedbed, with the temperature-sensing head close to the cutting base to accurately measure the temperature at the rooting site. After power is turned on, the electric heating wire begins to generate heat. When the temperature rises to 28°C, the propagation controller automatically regulates its operation to stabilize the hotbed temperature within the 28°C range.

The hotbed should activate the misting system 2-3 times daily to spray water and increase humidity, so that the cutting bases in the seedbed have sufficient moisture. If the seedbed is too dry, the cutting cortex will dry and wither and will not root; if there is too much water, it will cause cortex rot. Generally, plant cuttings in the seedbed for heat preservation and rooting promotion for about 10-15 days, when the callus tissue at the cutting base swells, root primordia turn white, and young root protrusions about 1 mm long grow; at this point they can be transplanted to the field nursery for planting. Transplanting too early or too late will both affect the survival rate of cuttings. When transplanting, the seedbed should be built into high beds, with a bed surface width of 1.3 m and unlimited length, depending on the terrain. First dig cutting trenches perpendicular to the bed surface, 15 cm deep, water thoroughly in the trenches, place cuttings vertically on one side of the trench at 10 cm plant spacing, then use fine soil to firm the cuttings, with terminal buds exposed on the bed surface. After planting, cover the bed surface with grass to preserve heat and moisture. After all transplanting is completed, water thoroughly once between beds to settle the roots.

vThis technique is especially suitable for the branches of trees and shrubs that shed their leaves in winter. After being treated, the branches are bundled or inserted closely and upright into the seedbed, and the optimum temperature at the base of the branches is regulated so that respiration of the injured cells at the wound is enhanced, enzymatic reactions are accelerated, and callus tissue or root primordia are produced as quickly as possible. Plants such as poplar, dawn redwood (Metasequoia glyptostroboides), mulberry, pomegranate, peach, plum, grape, ginkgo, and kiwifruit can all use the bare hardwood branches left after leaf fall for root promotion and propagation. It has the characteristics of a small footprint and high density (5000-10000 cuttings can be placed per 1 sq m).

(3) Mist propagation (air humidification and heating propagation) technique

vWhen propagating in the cold winter season, the air heating system needs to be turned on. Heat sources used for heating include air heating wires or oil-fired and gas-fired hot-air furnaces. After the heat source is installed, it is connected to a plant growth simulation computer to achieve automatic control so that the air temperature reaches the optimum. In addition, the mist propagation (or air propagation) technique used in rapid plant propagation provides a stable temperature for growth and rooting in a closed mist propagation chamber.

v1. Characteristics of mist propagation Mist propagation is carried out in a greenhouse or plastic shed. Current-year semi-lignified branches are fixed upright on a frame with a fixing rack, and through misting and heating the cuttings are kept under conditions of high humidity, suitable temperature, and a certain amount of light, so that they heal and root. Because the cuttings are under temperature, humidity, and certain light conditions more suitable than soil, mist propagation results in fast healing and rooting, a high rate of seedling formation, and a short propagation time. For example, with mist propagation, jujube reaches 80% rooting in 5 days, and pearl bush (Sorbaria kirilowii) can root 10 days after mist propagation, whereas soil cuttings take more than 1 month. The mist propagation method saves land and can make full use of the ground and space for multi-layer cuttings. It is simple to operate and easy to manage, and there is no need for operations such as digging up seedlings; the root system is not damaged and the transplant survival rate is high. It is not restricted by external environmental conditions, and a plant growth simulation computer automatically regulates temperature and humidity, making it suitable for factory-scale seedling production.

v2. Facilities and methods for mist propagation

v(1) Mist propagation chamber (or air propagation chamber) This is generally a greenhouse or plastic shed, and a misting device and cutting fixing racks must be installed inside.

v (2) Cutting bed To make full use of the indoor space, a bed is built on the ground with bricks, generally 1-1.5 m wide and 20-25 cm deep, with the length determined by the length of the greenhouse or shed. The bottom of the bed is covered with a 3-5 cm thick layer of crushed stone or cinder to facilitate drainage, and on top is spread a 15-20 cm thick layer of sand or vermiculite as the substrate. Walkways are left between the two beds and around them, and a 10 cm deep water ditch is dug on one side to facilitate drainage.

v(3) Cutting fixing rack Layered cutting fixing racks are set up on the cutting bed. One type is a support made of No. 8 galvanized wire arranged in parallel at a height of 2-3 cm above the bed surface, with a row spacing of 8-10 cm; each wire is bent into a "U"-shaped opening, with a plant spacing of 6-8 cm, so that the cuttings are held vertically in the openings. The other type is an aerial layered fixing rack. This kind of rack is mostly made of angle iron, with plastic boards placed on the rack. Equidistant "U"-shaped holes are cut on both sides of the boards, and the cuttings are fixed vertically in the holes. Movable baffles are set beside the holes to prevent the cuttings from falling out.

  (4) Misting and heating equipment To provide a suitable and stable environment for rooting of the cuttings in the air propagation chamber, artificial misting pipes must be installed above the shed frame, and the nozzles must be installed according to the misting distance. Fine mist is best. Through the plant growth simulation computer, the relative humidity in the chamber is controlled above 90%, the temperature is maintained at 25-30°C, and the light intensity is controlled at 600-800 Lx

v3. Management of mist propagation

v(1) Disinfection before cutting Because the air propagation chamber remains under high humidity and suitable temperature, this favors the growth and reproduction of pathogens. Therefore, attention must be paid to disinfection at all times. Before cutting, the air propagation chamber must be comprehensively disinfected, usually by spraying with a 0.4%-0.5% potassium permanganate solution. After cutting, about every 10 days, spray comprehensively with Bordeaux mixture at 1:100 to prevent fungal occurrence. If mold infection appears, spray diseased plants with 800-fold Tuzet to prevent spread, and in severe cases the plants can be pulled out and destroyed.

v(2) Control the temperature, humidity, and light of the air propagation chamber The cutting environment must be kept stable and suitable. If there is a sudden power outage, to prevent the cuttings from wilting, which can lead to bud regression and drying up, manual watering should be carried out promptly. In the high-temperature summer season, the indoor temperature often exceeds 30°C, so water should be sprayed promptly to lower the temperature, and windows should be opened temporarily for ventilation to regulate the temperature. In winter, use sunlight to raise the temperature during the day, and at night use heating wires to keep it warm, or use flues, hot-air furnaces, and the like to raise the temperature.

v  (3) Check the rooting of the cuttings in time When the new roots grow to 2-3 cm, they can be transplanted or potted in time. Before transplanting, the seedlings should undergo proper hardening, generally in a shade shed or an ordinary greenhouse, and after growth is stable they are moved to the open field.