Rational Irrigation Techniques and Maintenance Methods for Flowers and Nursery Stock

(1) The influence of water on the growth and development of flowers. Water is vital to all living things. Flowers are no exception. The fresh weight of common herbaceous and woody flowers is 40% to 95% water. Like temperature and light, water is an indispensable basic life factor for the survival and reproduction of flowers. Water conditions have a great influence on the growth, development, reproduction and dormancy of flowers, and even on changes in temperature and humidity in the site environment, as well as the occurrence and harm of pests and diseases. The main roles of water in flower growth are:

(1) Water is the main raw material for photosynthesis in flower plants. About 0.6 kg of water is needed to synthesize 1 gram of organic matter.

(2) Water is a solvent. The nutrients needed for flower growth and reproduction must be dissolved in water before they can be absorbed by flower roots.

(3) Water is a medium. Respiratory oxidation and various complex enzyme-catalyzed biochemical reactions in flower bodies must be carried out in an environment with water and with the participation of water.

(4) Water is the medium and driving force of transport. Flowers rely on water transpiration to maintain normal temperature and keep the water balance in the plant body. About 98% of the water absorbed by plants is used for transpiration, and only 2% remains in the body and is used to build the plant itself. No wonder a medium-sized annual flower needs to consume about 50 kg of water during its short life cycle of 4 to 5 months.

Water is an important guarantee for maintaining the normal life activities of cell protoplasm. The continuous renewal and exchange of water can maintain normal osmotic pressure in the plant body and keep flowers in a turgid state. For example, the standing upright of flower stalks, the extension of leaves, and the opening of flower buds are all inseparable from water.

The water content also directly affects the growth condition of flowers. For example, too much water will cause excessive growth of plants, inhibit flower bud differentiation, and also lead to root rot and disease occurrence; too little water will destroy the water balance in the plant body and cause flowers to wilt. Flower seeds can germinate only in a moist environment. A water content below 13% is a necessary condition for the safe storage and stable dormancy of most seeds. The overwintering, summering and dormancy of flowers also require good coordination with suitable water conditions. Soil water content has three different suitable states for any cultivated flower. When it is in the optimal state for survival, the water content at this time can effectively maintain the dynamic balance of water income and expenditure in the plant body and promote robust growth; when it is higher than the maximum water content that flowers can tolerate, root rot or death by suffocation will be caused by excessive soil water and lack of oxygen; if it is lower than the minimum water content that flowers can tolerate, growth will stagnate and flower buds will fall off because the root system cannot absorb enough water, and eventually the plant will gradually lose water, dry up and die.

The amount of soil water content has a great influence on air humidity, and therefore also indirectly affects the growth of flowers. When air humidity is too high, it has adverse effects on flowers, often causing excessive growth of branches and leaves and becoming a cause of flower drop. In addition, because the plant body grows weakly, its resistance to pests and diseases is reduced. During the maturity stage, excessive humidity hinders flowering and affects fruiting. However, among greenhouse plants, quite a few species like relatively high air humidity. For example, many tropical foliage plants are instead affected in their growth if humidity is too low. While liking moisture, such plants also require suitable temperature; if the temperature cannot match, humidity should not be too high either.

Water content not only affects the normal growth of flowers, but also affects flower bud differentiation and flower color. In flower cultivation, measures such as reducing water and cutting off water are often used to promote flower bud differentiation. For example, greenhouse-cultivated Dendrobium (an orchid family plant) should undergo short-term water cutoff starting in mid-October to promote flower bud differentiation; otherwise, it often cannot bloom. For bulbous flowers, water is often the main factor determining the timing of flower bud differentiation. For example, for tulip flower bud differentiation, according to experiments, the less the water content, the earlier the differentiation. Bulbs produced in sandy land differentiate and germinate earlier because of lower water content. Early-dug bulbs have delayed differentiation due to high water content.

Flower color is relatively closely related to water, and only suitable humidity conditions can reveal the inherent color of each variety. Generally, when water is lacking, flower color becomes deeper. For example, white and light pink varieties of rose often become creamy yellow or deep pink under insufficient water conditions; the same is true for chrysanthemum. Experiments have shown that when water is lacking, color becomes deeper because more pigment is formed.

(2) Water requirement patterns of flowers

Due to differences in the water environment of their places of origin, various flowers have different water requirements, and the environmental conditions suitable for their growth are also not the same. They have also formed different adaptive modes in morphology and physiological structure. For example, cactus plants native to the desert zones of the Americas, in order to adapt to the dry environment with extremely scarce local rainfall and reduce water evaporation, have leaves that became strongly reduced and turned into needle-like forms during long-term evolution, and are covered with very thick cuticle and wax layers, which helps keep water in the body from evaporating. Even if no water is supplied for several consecutive years, they can still survive tenaciously. In contrast, most evergreen flowers from warm and humid zones have large, thin leaves, delicate tissues, and no dense, thick wax layer or cuticle protection, and their stomata are often open, causing large amounts of transpiration, which is very unfavorable for storing water in stem and leaf organs. In order to maintain the water balance in the plant body, sufficient water must be supplied regularly.

According to the water requirement habits of flowers and their adaptability to different water environments, common flowers are divided into the following types:

1. Aquatic flowers. They must grow in water. Their vegetative organs have highly developed aerenchyma and can continuously transport oxygen. Such flowers include lotus, water lily, Acorus gramineus, and so on.

2. Hygrophytic flowers. They can grow in soil where water is often saturated or in environments with high air humidity, and have relatively strong waterlogging resistance. Such flowers include narcissus, flower reed, ferns, Monstera deliciosa, Cyperus alternifolius, Alocasia, Aglaonema modestum, Impatiens walleriana, Commelina communis, and so on. Because their leaves are large and thin, tender and juicy, with a thin cuticle, inconspicuous wax layer, shallow root system and fewer branches, they often look poor or even die in dry and low-humidity environments. They are suitable for growing in environments with sufficient water supply and very humid conditions. During maintenance, the watering principle of preferring moisture over dryness should be followed.

3. Mesophytic flowers. They are suitable for growing under conditions of moist soil and good drainage. Both too dry and too wet environments are unfavorable to their growth. Their drought tolerance lies between xerophytes and hygrophytes, with certain differences depending on species and variety. For example, Osmanthus fragrans, Magnolia denudata, and Malus spectabilis are relatively drought tolerant, while Chimonanthus praecox, Nerium oleander, and Jasminum nudiflorum are relatively moisture tolerant, so water management cannot be completely the same. Generally, 60% soil water content can be maintained. For flowers that like lower soil moisture and higher air humidity, during maintenance, water should be continuously sprayed into the air or the humidity of the surrounding ground should be increased.

4. Xerophytic flowers. Most of them originate in arid desert zones and have formed unique morphological structures adapted to dry climate ecological environments, such as small leaves or reduced leaves, sunken stomata, or succulent stems, with well-developed root systems. Such flowers include cacti, Echeveria, Euphorbia milii, and so on. In cultivation and management, the watering principle of preferring dryness over moisture should be followed. Too much watering and too high air humidity instead easily cause root rot and damage from anthracnose, fusarium wilt, and so on.

The water requirements of flowers for soil moisture differ at different growth and development stages. Generally speaking, after sowing, relatively high soil moisture is needed to moisten the seed coat, make it swell, and facilitate the germination of the radicle and plumule; after the seeds germinate and emerge, the root system is relatively shallow and the seedlings are very slender and weak, so the surface soil should be kept moderately moist; afterward, in order to prevent excessive growth of seedlings and promote plant maturity, soil moisture should be reduced, which is the so-called seedling hardening. Hardening seedlings at the seedling stage is one of the effective measures for cultivating strong seedlings; when growth reaches a certain point, relative drought (called water withholding or water control in flower cultivation) can also stop branches from accelerating growth and accumulate nutrients to supply flower bud differentiation. Flower bud differentiation is the turning point from vegetative growth to reproductive growth. At this time, properly controlling water for plum blossom, peach blossom, Prunus triloba, kumquat, Lagerstroemia indica, Cercis chinensis, and so on, and reducing or stopping watering several times, can inhibit or delay the growth of stems and leaves, advance and promote flower bud formation and development, and thereby achieve the ornamental goal of abundant flowers and heavy fruit. However, during the flowering period of flowers, soil water supply should be maintained at an appropriate level. Too little water makes flowering poor and shortens the flowering period, while too much water can also cause flower and bud drop. In addition, air humidity also affects flowering. Too low humidity shortens the flowering period and prevents the inherent flower colors of various kinds from being displayed. But too high humidity can also cause petal mildew and the spread of pests and diseases.

Overall, the water requirement characteristics of flowers are as follows: water demand increases during seed germination and seedling growth stages; sufficient water is necessary during the stem and leaf vegetative growth stage; water supply should be properly controlled during flower bud differentiation; water demand is greatest when entering the bud and flowering stages; and water demand is again relatively low in the later fruit and seed maturation stage. Therefore, watering should be carried out according to the water requirements of flowers at each developmental stage, so that flowers grow robustly, with lush branches and leaves, green and dripping with freshness, full of splendor.

(3) Rational watering of flowers

Most of the water needed for flower growth is absorbed from the soil. Maintaining appropriate soil water content is a necessary condition for the normal development of flowers and for obtaining higher ornamental quality. Because the cultivation methods of flowers differ, there are certain differences in irrigation amount and irrigation time.

1. Rational watering of ground-planted flowers. Watering ground-planted flowers is relatively simple. In rainy areas, attention should be paid to drainage in production, especially timely drainage after rain. If there is a long drought without rain, proper irrigation is also needed to keep the soil moist and prevent the soil surface from cracking, so as not to tear the root system. Ground planting should never use flooding irrigation. Where conditions permit, parks and gardens may use sprinkler irrigation and drip irrigation.

In the arid and water-scarce north and in water-scarce seasons, in addition to adopting drought-resistant measures, timely and appropriate irrigation must be carried out according to rainfall conditions to meet the water needs of flowers and trees during their growth process.

The amount and frequency of irrigation for ground-planted flowers and trees mainly vary according to flower variety, growth stage, weather, and soil texture. Irrigation should be controlled according to soil dryness and wetness. In specific operations, the following points should be noted:

(1) Water according to the growing season of flowers. Looking at the whole year, summer has high temperatures and large evaporation, so more water is needed; in winter, ground-planted plants generally stop growing and temperatures are relatively low, so less water is needed, and no watering is done unless dry. As for a single day, watering is generally carried out in the morning, but in summer, because water evaporates quickly, another watering should be done around 4 p.m.; in winter, morning temperatures are low, and watering is instead unfavorable, so it is best to water at 10 to 11 a.m.

(2) Irrigate according to plant type and growth period. Broadleaf and moisture-loving plants should be watered more; small-leaved, needle-leaved, and cactus types should be watered less. At the seedling stage, less water should be given; when entering vigorous growth and flowering stages (for fruit-viewing types), more water should be given; when seeds mature, less water should be given; and during dormancy, watering should be controlled even more. In addition, the leaves of Sinningia speciosa and African violet and the flower buds of Gerbera jamesonii are prone to rot after being watered, and these special situations all require attention.

(3) Determine irrigation amount and frequency according to soil texture. Sandy soil has large porosity, strong water storage capacity, and is prone to drought rather than waterlogging, so it should be watered more. Clay soil is a mess when wet and like a knife when dry. While paying attention to waterlogging prevention, drought prevention should also be noted, with timely intertillage and loosening of the soil. The number of irrigations should be appropriately reduced, and the amount of water per irrigation should be increased as appropriate. Humus soil rich in organic matter has a loose texture and large water-holding capacity, and is neither too prone to drying nor too prone to waterlogging. Under the same conditions, both irrigation amount and frequency can be correspondingly reduced.

2. Rational watering of potted flowers. Watering potted flowers is similar to watering ground-planted flowers. Both must consider water quality and water temperature, and also choose appropriate watering timing and amount according to the moisture-loving requirements of various plants, their growth and development stages, their current growth vigor and appearance, and weather changes, watering according to the sky and according to the flowers. The root system of potted flowers is limited to a certain space, so watering is more complicated than for ground planting. Potted flowers also require special attention to watering according to the pot.

(1) Watering according to the sky mainly means deciding whether watering is needed and how much water is needed according to seasonal and weather changes. In specific operations, the following points should be noted:

① Look at the season: In spring, temperatures rise, flowers and trees wake from dormant sleep, leaf buds sprout rapidly, some flower buds begin to grow, and the water demand of potted flowers begins to increase. Especially in the north, where spring drought and wind are common, the first watering after potted flowers are moved outdoors must be thorough. Afterward, as spring temperatures gradually rise, plant vegetative bodies expand, and transpiration and evaporation strengthen, the number of waterings should gradually increase and the interval between two waterings should be shortened. Generally, it can change from watering once every 2 to 3 days in early spring to watering once every 1 to 2 days. For spring-sown annual flowers and trees, because they are still at the sowing and emergence stage, the seedlings are small and grow relatively slowly and consume little water; watering too much at ordinary times will instead lower the soil temperature in the pot and affect seedling growth. In summer, the weather is clear and hot, sunlight is intense, and it is also the season when most flowers grow and develop most vigorously. At this time, leaf transpiration and soil surface evaporation increase sharply. Only by further increasing watering frequency and amount can the water requirements of flowers be met. On sunny days, water at least once a day. During the dog days, the weather is even hotter, and continuous clear, hot, and dry weather often occurs, causing strong evaporation from the pot surface and a sharp drop in soil moisture in the pot. This is precisely the season when potted flowers need the most water and consume the most water in the whole year. Drought damage is a serious threat to potted flowers during summer. A slight carelessness can cause wilting due to drought or even death. Therefore, on sunny days, water once in the morning and once in the evening. In special cases, when the pot soil turns white and dry, additional timely watering is needed. However, for potted flowers that are dormant or semi-dormant in summer, such as Cyclamen, the number and amount of watering should be reduced. Keep them moderately dry as much as possible, but not too dry, because being too dry is also unfavorable for flowers and trees dormant through the summer. Autumn is exactly the turning period from summer to winter. Sunshine weakens, temperatures gradually decline, and potted flowers and trees again enter a slow growth period. At this time, leaf transpiration and soil surface evaporation correspondingly decrease significantly compared with summer, and generally watering once every 2 to 3 days is enough. Winter is the season with the lowest temperatures of the year. Most potted flowers must be moved indoors to overwinter. The aboveground parts of deciduous flowers and trees wither after leaf drop and are in a dormant state. At this time, plant transpiration is negligible. Generally, if the pot soil is not too dry, no watering is needed. Water when dry and stop when wet; being appropriately on the dry side is instead beneficial for most flowers and trees to overwinter. Flowers in greenhouses generally need watering once every 1 to 2 weeks, and at most once every 4 to 5 days can basically meet their needs. Never water too much or too frequently.

② Look at the weather: Different watering methods should be adopted for different weather, and watering should be carried out timely and appropriately according to weather change trends. In dry and windy weather, water more and water thoroughly; in cloudy weather when rain is forecast, stop watering, water less, or delay watering; in continuous rainy weather, not only is watering unnecessary, but accumulated water in the pot should also be drained at any time, and after the rain stops, attention should also be paid to withholding water. In weather with high relative humidity, water less and let the pot soil be on the dry side; if there was little rain earlier, relative humidity is low, and no rain is forecast in the future, water more.

(2) Watering according to the flowers. Watering according to the flowers means choosing the appropriate watering timing and suitable watering amount according to the moisture-loving requirements of various flowers, their growth and development stages, and their current growth vigor and appearance. In specific operations, the following issues should be noted:

① Determine watering time and amount according to flower type and variety: Water more for flowers that like moisture and need more water; water less for flowers that like dryness and need less water. Generally, herbaceous flowers have tender stems and leaves and need more water; woody flowers have hard stems and need less water. Cacti and other succulents prefer dryness over moisture; bulbous and cormous flowers should not remain wet or overly wet for long; peonies and other fleshy-rooted plants like dryness and dislike moisture, so they should not be watered much; aquatic flowers like water and fear drought. Broadleaf and many-leaved flowers with large crown diameters should be watered more, while narrow-leaved and small-leaved flowers with small crown diameters should be watered less.

② Determine watering time and amount according to the growth and development stage of flowers: Flowers in the vigorous growth stage need more water and should be watered more; flowers in the slow growth stage need less water and should be watered less. Most flowers do not need much water at the seedling stage, and watering should be properly controlled during seedling hardening. During the vigorous growth period, the pot soil should be kept regularly moist. Some woody flowers also need proper water control before flowering, and normal watering should resume only after flower bud differentiation ends. When entering the flowering period, the pot soil should alternate between dry and wet, and after flowering the pot soil should not be too wet. During the seed and fruit maturation stage, the pot soil should be slightly on the dry side. During dormancy, the number and amount of watering should be reduced, as long as the soil is kept from becoming excessively dry. Whether potted flowers need watering is often reflected in their external morphology. For example, wilting of new leaves, young leaves, young buds, and young flowers indicates that the flowers have begun to lack water, and the severity of the wilting can roughly reflect how much water is needed; conversely, excessive growth of the plant, thin and tender stems, thin and yellow leaves, and sparse flower buds indicate excessive watering. Sometimes after being damaged by excessive moisture, flowers also show symptoms commonly seen in drought-stressed flowers, such as yellowing leaves, leaf drop, and flower drop. It is necessary to distinguish these to decide whether to water. If the plant indeed shows severe wilting symptoms such as drooping leaves and tender branches due to drought, it is best not to water immediately. Instead, first move the potted flower to a shady place, water a little, and after the branches and leaves basically return to normal, water thoroughly, and it can recover its vitality. If the cause is long-term excessive water in the pot, the potted flower should be promptly moved to a well-ventilated, shaded place, fertilizing should be stopped, watering should be strictly controlled, attention should be paid to clearing the drainage holes, and deep intertillage and soil loosening should be carried out in time to promote water evaporation and improve aeration in the root zone. Spraying a small amount of water mist on the wilted branches and leaves also helps root healing and recovery and maintains the water balance in the plant body. If the wilting is caused by overly concentrated fertilizer application, shade should be provided immediately and water should be applied repeatedly to reduce the excessively high soil solution concentration. At the same time, the bottom of the pot should be raised to promote the rapid overflow of excess water from the bottom hole. Special attention should be paid to the fact that some potted flowers with relatively strong drought-loving characteristics do not show abnormal external morphology when they first begin to suffer drought, but once obvious wilting truly appears, it will inevitably affect the ornamental effect of the plant. Watering at that time is obviously too late. Therefore, judging whether potted flowers need watering from external morphology is sometimes not completely reliable.

(3) Watering according to the pot. Potted flowers require special attention to watering according to the pot. In specific operations, the following points should be noted:

① Look at the size of the flower pot: A small pot holds limited soil and stores less water, and has a relatively large surface area, so it loses more water and dries faster than a large pot. Therefore, small pots should be watered more frequently and in smaller amounts. However, the amount of water per watering should be slightly larger for large pots than for small pots; otherwise, the phenomenon of halfway watering easily occurs. If a small pot cannot meet the need, it should be promptly replaced with a larger pot.

② Look at the texture of the flower pot: Commonly used clay pots have a relatively rough texture, and the pot walls contain countless tiny pores. These pores have strong water seepage and air permeability, and the water lost through these pores every day is also considerable. In contrast, purple clay pots, glazed ceramic pots, and so on have very fine textures and few pores in the pot walls, and their water seepage and air permeability are too poor. Pots with rough texture need to be watered more frequently, and the amount each time needs to be larger, while when using ceramic pots to grow flowers, watering must never be too much or too frequent, otherwise root rot and death are extremely likely. For old clay pots, because the pores in the pot walls have mostly been blocked by mud, the watering frequency and amount should also be reduced as appropriate.

③ Look at the soil texture in the pot: Soil with a relatively heavy sandy nature has a coarser texture, large porosity, fast water seepage, small water-holding capacity, and weak water retention, and is prone to drought rather than waterlogging, so the watering frequency should be appropriately increased. Clayey pot soil is a mess when wet and like a knife when dry. While paying attention to waterlogging prevention, drought prevention should also be noted. Timely intertillage and soil loosening to break up surface crusting of the pot soil can appropriately reduce watering frequency, while the amount per watering should be increased as appropriate. Humus soil rich in organic matter has lower pot surface evaporation, a loose texture, and large water-holding capacity, so water supply and frequency should be appropriately reduced.

④ Look at the color and weight of the pot soil: When dry, soil color becomes lighter, weight becomes lighter, and hardness increases. Moist soil is the opposite. Therefore, if your pot soil is whitish in color, relatively light in weight, and hard to the touch, it means the pot soil is already dry and should be watered more in time. If the pot soil still appears dark gray or dark brown, is heavy in weight, and feels soft to the touch, it means the soil is moist and does not yet need watering for the time being.

⑤ Listen to the sound of the pot: When you gently tap the flower pot with your finger, if the pot wall gives a crisp, bright sound, it indicates that the pot soil is on the dry side and should be watered; if the pot wall gives a low, dull, turbid sound, it indicates that the pot soil is on the wet side and does not yet need watering for the time being.

⑥ Check whether there are abnormal conditions needing treatment: For example, newly potted flowers often show separation between the pot and the soil when soil moisture is insufficient. At this time, if a large amount of water is applied directly, it will inevitably cause water to flow rapidly out through the bottom hole along the separated cracks. In this situation, it is best to first block the cracks around the pot wall with potting soil, then slowly pour in a small amount of water, and after the pot soil is soaked, water according to the conventional method.