How to regulate the concentration of the growing medium solution

The medium solution contains a certain amount of salt and has a certain water potential. The water potential of the medium is higher than that of the root cells, so the roots can absorb water well. However, if the medium contains too much salt, or if fertilizer is applied too concentratedly, so that the water potential of the medium drops below that of the root cells, the roots can no longer absorb water, and the orchid plant will show wilting. In severe cases, the orchid plant can be "burned to death." Because Chineseorchidsare grown usingcultivationmedia that are rather special and have a weak buffering capacity against salts themselves, it is easy for the medium solution concentration to become too high, so fertilizer should be applied more dilute. Chineseorchidshavestrict requirements for the moisture of the growingmedium, which is not easy for beginners to grasp. Is there after all aquantified indicator for the moisture content of the growingmedium? What is the optimal moisture content of the growing medium? According to tests by scholars, if a medium with a moisture content of 51.66%, which reaches 100% of maximum water-holding capacity, is used as the test medium,Cymbidium sinensehas an optimal growing medium moisture content of 70%-90% of the medium's maximum water-holding capacity, at which time the growth rate and photosynthetic rate are greatest, that is, the growing medium moisture content is best at 36%-46%. If it is below 50% of maximum water-holding capacity, growth is hindered or even death occurs. Therefore, when watering or supplementing moisture for Chineseorchids, this indicator can be referenced for quantified management. Especially in some high-grade orchid growing sites, automatic control of water management can be carried out according to this indicator, and it is particularly suitable for drip irrigation. The processes of water absorption and transpiration by the orchid plant are the two ways in which the orchid plant exchanges water with the external environment, and water transport closely links these two ways. Through water absorption and transpiration, the water in the orchid plant body is maintained in a balanced state, thereby allowing all life activities to proceed normally. Transpiration causes the orchid plant to lose a large amount of water, but it is the driving force for the plant's passive water absorption. Root pressure alone cannot maintain the balance of water metabolism; only the strong pulling force formed by transpiration can enable large amounts of water to be absorbed or to rise rapidly. Through transpiration, the plant promotes the absorption and conduction of mineral elements within the body, causing water-soluble salts to be distributed rapidly to all parts. Moreover, transpiration can lower leaf temperature. When the orchid plant carries out photosynthesis, it must absorb a large amount of light energy, most of which is converted into heat energy; in addition, when the plant body carries out respiration, it also produces a large amount of heat energy. All of these can raise body temperature. If the plant body temperature exceeds a certain limit, normal physiological activities will be affected. Because the vaporization of water during transpiration consumes a great deal of heat energy, it can lower leaf temperature, preventing the leaves from being "scorched" under the blazing sun. If the leaves and roots of the orchid plant are not sound, then when encountering weather with strong transpiration, the leaves are often easily scorched, so attention should be paid to this problem during cultivation. When frost occurs, because a thin layer of frost forms on the leaves, if at this time the water absorption and transpiration of the orchid plant roots weaken, the leaves will be frostbitten, especially the relatively old leaves, which is mainly due to the weakened water absorption and transpiration of aging leaves. For this reason, when encountering this kind of weather, before the frost melts, draw well water and spray it on the leaves to make it melt. This mainly causes the frost layer to absorb heat from the water and break down, without needing to absorb heat from the leaves, maintaining the body temperature of the orchid leaves so that the orchid leaves remain intact and are not frostbitten. The stomata of orchid leaves can open and close freely to diffuse water vapor, thereby regulating transpiration. Therefore, the structure of the leaves and the degree of stomatal opening are all closely related to transpiration. BecauseCymbidium sinensehas a large leaf area, and leaves that are softer with a thin cuticle have greater transpiration, compared withCymbidium goeringii、Cymbidium kanranit will be less. As for the tiger-head orchid type (C. hookerianum), because its cuticle is relatively thick, its transpiration is weaker, and its water requirement is relatively less than that ofCymbidium sinense. And different varieties of the same species have different leaf structures, so their transpiration also differs, leading to differences in water management measures. Therefore, management should be targeted. However, in addition to internal factors such as leaf structure affecting transpiration, it is also affected by external environmental conditions. (Liu Zhongjian, Xu Gongming)