The Effect of Water in Orchid Environmental Factors on Growth

Mostorchidsgrow in rainy but well-drained environments, so they are fond of moisture but afraid of excessive water retention. However, different species oforchidshave different water requirements, and incultivationthey must not be mixed together. For example, compared with many hybrids of Paphiopedilum, Cattleya needs more sunlight, lower temperatures and less water, so they cannot be placed in the same environment, or at least not on the same shelf. Also, using bark, pebbles or clay lumps ascultivationmedium evaporates much faster than using sphagnum moss, Osmunda fern or foam plastic as a medium. Orchids grown in different mediaOrchidalso cannot be placed together. In this way, they can be watered in whole blocks as needed without confusion. Rainwater, snow water and natural soft water (river water, well water) are the best water for orchids. But in heavily polluted cities, rain and snow may also contain harmful substances. Try to avoid using hard water and artificially softened water; the latter (for example, using ion exchange resins) turns the calcium in the water into sodium during treatment, and sodium is more harmful toorchidsthan calcium. The frequency of watering varies with the seasons; in summer, water frequently, while in winter it must be strictly controlled. As for the time of watering, except for the scorching heat at noon and the cold at night, any other time during the day is fine. Generally, green plants absorb water during the day. At this time the stomata open, absorbing carbon dioxide, and through chlorophyll they absorb solar energy to carry out photosynthesis, synthesizing carbon dioxide and water into organic matter; at the same time, they also lose water through transpiration. At night, through respiration, with the participation of oxygen, organic acids are decomposed into carbon dioxide and water, producing energy for plant growth and releasing carbon dioxide and water. Most terrestrial orchids, including the terrestrial orchids among Chinese orchids, Cypripedium, and most Paphiopedilum, belong to this type. That is to say, they absorb water during the day and release water at night. Therefore, water should be given when the plants are absorbing water during the day, preferably when the temperature begins to rise, especially in winter, while in summer it is fine after the sun rises. This is mainly to avoid too great a difference between the water temperature and the temperature of the plant (mainly the roots), which would harm the absorption function of the roots. In northern greenhouses, special attention should be paid to this point when growing orchids. Some books advocate watering Chinese orchids in the morning and evening, or even at night, but this is probably not necessarily reasonable. It is worth special mention that a considerable number of orchids, mainly thick-leaved epiphytic orchids, have physiological characteristics of drought tolerance. Cattleya, Dendrobium, Phalaenopsis and others all belong to this type. Because their method of fixing carbon dioxide is similar to that of crassulaceous succulent plants, it is called Crassulacean Acid Metabolism, abbreviated as CAM. This type of orchid opens its stomata at night, because the humidity in the air is highest at night (in nature), carbon dioxide is fixed and stored as malic acid, making the cell sap strongly acidic at night. During the day, the carbon dioxide is released for photosynthesis. The CAM metabolic type is an adaptation to xeric environments, because by not opening the stomata during the day, water loss can be reduced, while at night the humidity is high and there is abundant carbon dioxide in nature. But if water is sufficient, the stomata can also open during the day, absorbing carbon dioxide and carrying out photosynthesis. For this type of orchid, watering during the day or at dusk is both acceptable, as long as the water temperature is suitable and the watering is done properly. The amount of water should be such that the medium is moistened through. But exactly how many days between waterings depends on the orchidFloralspecies, medium,cultivationenvironment and local climatic conditions. Most important of all is for the grower to observe carefully and make judgments based on actual conditions. Usually the medium should not be allowed to dry out completely. When growing orchids with sphagnum moss or partly with sphagnum moss, if the sphagnum turns white, it indicates it is too dry; if bark, foam plastic or the like is used as the medium, although the surface may look dry, the inside may still be relatively moist, so careful observation is needed. In the north, there are certain difficulties in using natural water to irrigate orchids. And tap water is often disinfected with bleaching powder and is slightly alkaline. When tap water has to be used, it should first be poured into an artificial pond and stored for later use. As long as it is exposed to sunlight for a relatively long time, the chlorine will dissipate and the bleaching powder will settle. Because most orchids come from tropical and subtropical regions, where the pH of the medium and water is mostly pH 5.2-6. If the pH of the water is too high (above pH 7, that is, neutral or alkaline), it can be treated with hydrochloric acid, oxalic acid, acetic acid or citric acid to lower it to pH 5.2-6. Conversely, in a few areas in the south, when the water is too acidic, it can also be treated with caustic alkali, such as sodium hydroxide or potassium hydroxide. The method of watering also requires attention. Generally there is a distinction between pouring water, spraying water and soaking water. Pouring water means using the spout of a pot to pour water directly into the medium. Generally a long-spouted watering can should be used, avoiding the body of the can touching the orchid pot and the orchid; the water should be poured slowly, making sure to wet the medium through. Do not use a large-mouthed watering can or a tap water pipe to pour forcefully, so as to avoid splashing mud, contaminating the leaves, or causing bark and other media to float out of the pot, and also so as not to cause the medium temperature to rise or fall sharply. For spraying water, use a showerhead-type nozzle, and for seedlings use a small-hole nozzle, so as not to damage the tender leaves and stems. In addition, attention should also be paid to flower buds and flowers; do not let water enter them and cause rot. Spraying water has the effect of relieving and lowering excessively high room temperature. Soaking water means placing the flower pot into water, moistening the medium from the bottom up, just enough to wet it through, not too wet. In short, it must suit the orchid's characteristics of fearing both long drought and waterlogging, liking moisture but not wetness, and dryness but not aridity. (Chen Xinqi, Ji Zhanhe)