Key Technical Points and Practical Methods for Water-Saving Irrigation of Flowers
(1) The Effect of Water on the Growth and Development of Flowers
Water is vital to all living things, and flowers are no exception. The fresh weight of common herbaceous and woody flowers is 40%-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 the flower root system.
(3) Water is a medium. Respiratory oxidation and various complex enzyme-catalyzed biochemical reactions in the flower body must all take place in an environment with water and with the participation of water.
(4) Water is the medium and driving force for transport. Flowers rely on transpiration to maintain normal temperature and keep the water balance within 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 4-5 months. Water is an important guarantee for maintaining normal life activities of cell protoplasm. The continuous renewal and exchange of water can maintain normal osmotic pressure in the plant body, keeping flowers in a turgid state. For example, the uprightness of flower stalks, the extension of leaves and the opening of flower buds are all inseparable from water. Water content also directly affects the growth and development of flowers. For example, too much water can cause leggy growth of the plant, 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. Overwintering, oversummering 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 optimum 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 suffocation death will be caused by too much 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.
Soil water content has a great influence on air humidity, and therefore also indirectly affects flower growth. Excessive air humidity has adverse effects on flowers, often causing leggy growth of branches and leaves and becoming a cause of flower drop. In addition, because the plant body grows weak and tender, its resistance to pests and diseases is reduced. During the maturity stage, excessive humidity hinders flowering and affects seed set. However, among greenhouse plants, many species like relatively high air humidity. For example, many tropical foliage plants are instead affected in their growth if humidity is too low. While these plants like humidity, they also require suitable temperatures; 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 a short period of water cutoff starting in mid-October to promote flower bud differentiation; otherwise, it often fails to bloom. For bulbous flowers, water is often the main factor determining whether flower bud differentiation occurs early or late. For example, according to experiments on flower bud differentiation in tulips, the less the water content, the earlier the differentiation. Bulbs produced in sandy soil differentiate earlier because of their low water content. Bulbs dug early have delayed differentiation due to high water content.
Flower color is relatively closely related to water, and only suitable humidity conditions can bring out 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 turn creamy yellow or deep pink under insufficient water conditions; the same is true for chrysanthemums. Experiments have shown that when water is lacking, color becomes deeper because more pigment is formed.
(2) Water Requirement Patterns of Flowers
Because of 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 areas of the Americas, in order to adapt to the dry environment with extremely scarce local rainfall and reduce water evaporation, had their leaves strongly reduced and miniaturized during long-term evolution, becoming needle-like, and covered with very thick cuticle and wax layers. This helps keep water in the body from evaporating, so that even if no water is supplied for several years in a row, they can still survive tenaciously. In contrast, most evergreen flowers from warm and humid areas have large, thin leaves, tender tissues, and no dense, thick wax layer or cuticle protection, and their stomata are often open, causing a very large amount of transpiration. This is very unfavorable for water storage in stem and leaf organs. In order to maintain the water balance in the plant body, sufficient water must be supplied frequently.
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 that can continuously transport oxygen. Such flowers include lotus, water lily, Acorus gramineus and so on.
2. Wetland flowers. They can grow on soil where water is often saturated or in environments with high air humidity, and have relatively strong tolerance to waterlogging. Such flowers include narcissus, flower rush, 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 thin cuticle and inconspicuous wax layer, and their root systems are shallow and have few 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 high humidity. During maintenance, the watering principle of preferring wet over dry 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, white magnolia and crabapple are relatively drought-tolerant, while wintersweet, oleander and winter jasmine are relatively moisture-tolerant, so water management cannot be completely the same. Generally, 60% soil water content can be maintained. For flowers that prefer 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 areas and have formed unique morphological structures adapted to dry climate ecological environments, such as small leaves or reduced leaves, sunken stomata, succulent stems, and well-developed root systems. Such flowers include cacti, Echeveria, Euphorbia milii and so on. In cultivation management, the watering principle of preferring dry over wet should be followed. Too much watering and excessive air humidity tend to 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 humidity 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 from the soil, 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 leggy growth of seedlings and promote plant maturity, soil humidity 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, for plum blossom, peach blossom, Prunus triloba, kumquat, crape myrtle, redbud and so on, appropriately controlling water 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, thereby achieving the ornamental goal of abundant flowers and heavy fruit. However, during the flowering period of flowers, the supply of soil moisture should be kept at an appropriate level. Too little water results in poor flowering 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 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; sufficient water is necessary during the stem and leaf vegetative growth stage; water supply should be appropriately 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 luxuriant branches and leaves, verdant and lush, presenting a splendid scene.
(3) Rational Irrigation 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, their irrigation amount and irrigation time differ to a certain extent.
1. Rational watering of field-grown flowers. Watering field-grown 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, appropriate irrigation is also needed to keep the soil moist and prevent the soil surface from cracking, so as not to tear the root system. Field planting should never use flood irrigation. Where conditions permit, 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-resistance 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 field-grown flowers and trees mainly vary according to flower variety, growth stage, weather and soil quality. Irrigation should be controlled according to soil dryness and wetness. In specific operations, the following points should be noted:
(1) Irrigation should be carried out according to the growing season of the flowers. Over the whole year, summer has high temperatures and large evaporation, so more irrigation is needed. In winter, field-grown plants generally stop growing and temperatures are relatively low, so less irrigation is needed, and if not dry, do not irrigate. Within a single day, irrigation is generally carried out in the morning, but in summer, because water evaporates quickly, another irrigation should be given around 4 p.m.; in winter, the morning temperature is low, and irrigation is instead unfavorable, so it is best to irrigate from 10-11 a.m.
(2) The irrigation amount and frequency should be determined according to soil quality. Sandy soil has large porosity, strong water storage capacity, and is easy to dry but not easy to become waterlogged, so it should be irrigated more. Clay soil is a mess when wet and like a knife when dry. While paying attention to waterlogging prevention, attention should also be paid to drought prevention, timely cultivating and loosening the soil, appropriately reducing the number of irrigations, and increasing the amount of water per irrigation as appropriate. Humus soil rich in organic matter has a loose texture and large water-holding capacity. It is neither too easy to dry nor too easy to become waterlogged. Under the same conditions, both the irrigation amount and frequency can be correspondingly reduced.
(3) Irrigation should be carried out according to plant type and growth period. Broad-leaved and moisture-loving plants should be irrigated more, while small-leaved, needle-leaved and cactus plants should be irrigated less. At the seedling stage, less irrigation should be given; when entering the vigorous growth period and flowering period (for fruit-viewing types), more irrigation should be given; when seeds mature, less irrigation should be given; and during dormancy, irrigation should be controlled even more. In addition, the leaves of gloxinia and African violet and the flower buds of Gerbera jamesonii are prone to rot after being watered. These special situations all require attention.
2. Rational watering of potted flowers. The watering of potted flowers is similar to that of field-grown flowers. Both must consider water quality and water temperature, and also choose appropriate watering timing and amount according to the moisture-preference requirements of various plants, their growth and development stages, their current growth vigor and appearance, and weather changes, watering by observing the sky and watering by observing the flowers. The root system of potted flowers is limited to a certain space, so watering is more complicated than for field planting. Potted flowers also require special attention to watering by observing the pot.
(1) Watering by observing the sky mainly means deciding whether irrigation is needed and how much water is needed according to seasonal and weather changes. In specific operations, the following points should be noted:
① Observe the season: In spring, temperatures rise, flowers and trees wake from deep dormancy, 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. Later, as spring temperatures gradually rise, the plant's vegetative body expands, and transpiration and evaporation strengthen, the number of waterings should be gradually increased and the interval between two waterings shortened. Generally, it can change from watering once every 2-3 days in early spring to watering once every 1-2 days. For spring-sown annual flowers and trees, because they are still at the sowing and seedling emergence stage, the seedlings are small and grow relatively slowly, and water consumption is low. 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 the number of waterings and the amount of water can the water requirements of flowers be met. On clear days, water at least once a day. During the dog days, it is even
hotter, and continuous clear, high-temperature 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 oversummering. A slight carelessness can cause wilting due to drought or even death. Therefore, on clear days, water once in the morning and once in the evening. In special cases, when the pot soil turns white and dry, timely supplementary water is also needed. However, potted flowers that are in a dormant or semi-dormant state in summer, such as cyclamen, should have the number of waterings and the amount of water reduced. Try to keep them moderately dry, but not too dry; being too dry is also unfavorable for flowers and trees dormant through the summer. Autumn is 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. Generally, watering once every 2-3 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 fall 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 the overwintering of most flowers and trees. Flowers in greenhouses generally need watering once every 1-2 weeks, and at most once every 4-5 days can basically meet their needs. Never water too much or too frequently.
② Observe the weather: Different watering methods should be adopted for different weather, and watering should be carried out timely and appropriately according to weather 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; when there was little rain earlier, relative humidity is low, and no rain is forecast in the future, water more.
(2) Watering by observing the flowers. Watering by observing the flowers means choosing the appropriate watering timing and suitable watering amount according to the moisture-preference 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 The watering time and amount should be determined according to the type and variety of flowers: moisture-loving flowers with high water demand should be watered more; drought-loving flowers with low water demand should be watered less. Generally, herbaceous flowers have tender stems and leaves and need more water; woody flowers have hard stems and need less water. Cacti and other succulent plants prefer dry over wet; bulbous and cormous flowers should not be wet for a long time or too wet; peonies and other fleshy-rooted plants like dryness and dislike wetness, so they should not be watered much; aquatic flowers like water and fear drought. Broad-leaved 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 The watering time and amount should be determined according to the growth and development stage of the 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 appropriately controlled during the seedling hardening stage. During the vigorous growth period, the pot soil should be kept often moist. Some woody flowers also need appropriate 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 of waterings and the amount of water should be reduced, and it is enough to keep the soil from becoming excessively dry. Whether potted flowers need watering is often reflected in their external morphology. For example, if new leaves, tender leaves, young buds and young flowers wilt, it indicates that the flowers have begun to lack water. The degree of wilting can roughly reflect how much water is needed. Conversely, leggy growth of the plant, thin and tender stems, thin and yellow leaves, and sparse flower buds indicate excessive watering. Sometimes flowers suffering from moisture damage also show symptoms common to drought-stressed flowers, such as yellow leaves, leaf drop and flower drop. A distinction must be made in deciding 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 cool place, water a little, and after the branches and leaves basically return to normal, water thoroughly, and it can recover vitality. If it is because the pot has had excessive water for a long time, the potted flower should be promptly moved to a well-ventilated and shaded place, fertilization should be stopped, watering should be strictly controlled, attention should be paid to clearing the drainage holes, and deep cultivation and loosening of the soil 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 plant wilting is caused by overly concentrated fertilization, then shading should be applied immediately and water should be poured 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 tolerance do not show abnormal external morphology when drought stress first begins, but once obvious wilting truly appears, it will inevitably affect the ornamental effect of the plant. Watering at this time is obviously too late. Therefore, judging whether potted flowers need watering from external morphology is sometimes not completely reliable.
(3) Watering by observing the pot. Potted flowers require special attention to watering by observing the pot. In specific operations, the following points should be noted:
① Observe the texture of the flower pot: Commonly used clay tile pots have a relatively rough texture, and there are countless tiny pores in the pot wall. 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 ceramic pots, colored glazed porcelain pots and so on have a very fine texture, few pores in the pot wall, and poor water seepage and air permeability. Pots with rough texture need to be watered more often, and the amount of water each time needs to be larger. When using ceramic pots to grow flowers, never water too much or too frequently; otherwise, root rot and death are very likely. For old clay tile pots, because most of the pores in the pot wall have been blocked by mud, the number of waterings and the amount of water should also be reduced as appropriate.
② Observe the size of the flower pot: Small pots have limited soil capacity and store less water, and because their surface area is relatively large, they lose more water and dry faster than large pots. Therefore, small pots should be watered more frequently and with less water each time. However, the amount of water per watering should be slightly larger for large pots than for small pots; otherwise, the phenomenon of water only reaching halfway may easily occur. If a small pot cannot meet the needs, it should be promptly replaced with a larger pot.
③ Observe 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 feels hard, it indicates that the pot soil is already dry and more water should be given in time. If the pot soil is still dark gray or dark brown, heavy in weight, and feels soft, it indicates that the soil is moist and there is temporarily no need to water.
④ Observe the soil quality in the pot: Soil with a relatively high sand content has a coarser texture, large porosity, fast seepage, small water-holding capacity, and weak water retention. It is easy to dry but not easy to become waterlogged, so the number of waterings should be appropriately increased. Heavily clayey pot soil is a mess when wet and like a knife when dry. While paying attention to waterlogging prevention, attention should also be paid to drought prevention. Timely cultivating and loosening the soil and breaking up surface crusting of the pot soil can appropriately reduce the number of waterings, while the amount of water per watering should be increased as appropriate. Humus soil rich in organic matter has lower evaporation from the pot surface, a loose texture, and large water-holding capacity, so the water supply and frequency should be appropriately reduced.
⑤ Listen to the sound of the pot: When you gently tap the flower pot with your finger, if the pot wall emits a crisp, bright sound, it indicates that the pot soil is on the dry side and should be watered; if the pot wall emits a low, dull, muddy sound, it indicates that the pot soil is on the wet side and there is temporarily no need to water.
⑥ Observe whether there are abnormal conditions requiring treatment: For example, when newly potted flowers lack sufficient soil moisture, separation between the pot and the soil often occurs. At this time, if a large amount of water is poured directly, it will inevitably cause water to quickly drain away through the bottom hole along the separated cracks. In this case, 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 moistened, water according to the conventional method.