Analysis of the causes of orchid root rot and prevention methods

In winter, orchids are in a dormant or slow-growth stage, so the potting medium should be kept on the dry side; spring and early summer are important periods for orchids to root and grow leaves, so the potting medium should be kept slightly moist; however, prolonged excessive moisture can also easily cause root rot, leading to yellowing leaves and even death. This is because excess water causes waterlogging in the soil, poor aeration, and insufficient oxygen, which hinders root respiration and causes the root system to turn black and rot. During the plum rain or heavy rain season, potted orchids must be protected from harm, because with prolonged rain and high humidity, black spots are most likely to appear on new leaves, and the flower buds often show a "rotten sheath" phenomenon, affecting flowering and ornamental value. However, if the potting medium is too dry, it easily causes the pseudobulbs to shrivel or other tissues to lose water, affecting metabolism, and can also lead to weak tissues and poor plant growth. In autumn, the potting medium should be kept on the moist side to favor leaf growth and proper flowering the following year. Therefore, orchid growers should understand the key principle of "not wet in winter, not dry in autumn." The above explains the different water requirements of orchids at different stages, so the amount of watering should be strictly controlled according to these requirements. At the same time, improper fertilization of orchids can also easily cause root rot; for example, applying too much fertilizer, too concentrated fertilizer, or pouring liquid fertilizer into the leaf sheaths can all have adverse effects on orchids. When fertilizing, the amount of fertilizer should also be increased or decreased according to the amount of watering, so that they grow in harmony.

To cultivate a good pot of orchids, one must first start by growing the orchid roots well. Only when the root mass develops vigorously and the root system's functional capacity is well developed can the absorption and transport of water and nutrients, photosynthesis, respiration, and energy storage and accumulation proceed normally, and only then will growth rate, reproductive capacity, and flowering rate be enhanced. Otherwise, if the root system is poor or rots and is lost, the absorption and transport of water and nutrients will be blocked, photosynthesis, respiration, and other capacities will decline, and the orchid will gradually decline and die. Orchid root rot is mainly caused by the following two aspects:

(1) The growing medium lacks the function of draining water and allowing air movement. Water is the source of all things, and orchid growth must have water in order to absorb and transport nutrients and carry out normal metabolism. Orchids are epiphytic root plants. During their growth, a small part of the water they need comes from moisture in the air, but most of the water must be absorbed from the water contained in the growing medium, and orchid roots must also absorb oxygen from the pores of the medium in the pot for respiration. If the medium in the pot drains poorly and has too high a water content, water will fill the pores of the medium, causing waterlogging. When the pores of the medium are filled with water and lack oxygen, the roots suffocate from oxygen deficiency, and over time the root function gradually deteriorates; at this point, because harmful pathogens invade and multiply, the root system will rot as a result. 

(2) The water quality is not clean or the pH value of the water is unsuitable. The water used for orchids must be clean and unpolluted. If unclean water is used, some harmful pathogens or toxins will erode and contaminate the orchid roots, causing serious disease in the root system, stems, and leaves, with the roots turning black and rotting and the orchid plant dying. The pH value of water used for orchids must be between 5.5 and 6.5. If the pH value is below 5, it is on the acidic side, which will restrict the absorption of major elements such as nitrogen, phosphorus, and potassium by orchid roots, and the orchid plant will lack major nutrients and show yellowing leaves. In an acidic environment, soil-borne pathogens such as root rot fungi are most suited to growth and reproduction, harming the root system and accelerating orchid root rot and death; if the pH value is above 8, it is on the alkaline side, and alkaline water and medium will create obstacles to the absorption of trace elements needed for orchid plant growth. If orchid roots and plants cannot obtain the nourishment of trace elements, they will gradually wither and die. In response to the above two problems, some corresponding measures need to be taken during cultivation: 

(1) Select and prepare a good orchid growing medium. The orchid growing medium should drain water and allow air movement, be moist but not waterlogged, and dry but not parched. There are many special orchid growing media sold on the market now, and they are also very suitable, such as Emei Mountain soil from Sichuan, expanded clay from Chongzhou, and various special orchid soils from Guangdong; all are very good orchid cultivation media. A portion of leaf mold can also be mixed into these media to supplement insufficient fertility. Local materials can also be used, such as weathered soil, crushed brick granules, crushed charcoal granules, crushed oak bark, etc., mixed with an appropriate amount of leaf mold; the effect is also very good, as it can drain water and allow air movement, retain moisture without waterlogging, and also have a certain fertility. However, note that the materials used must be non-toxic, sterile, unpolluted, and free of parasitic insect eggs; otherwise, they will also harm the orchid root system. 

(2) The water used to irrigate orchids must be clean. Polluted water and unclean water cannot be used. Many orchid books say that stream water and river water are most suitable for orchid growth, but most orchid enthusiasts live in cities and are not professional orchid garden operators, so it is very difficult to meet this requirement. As for watering orchids with tap water, from many years of practice the author has found the effect to be very good. If conditions permit, putting tap water in a bucket or basin for a few days to let the chlorine in the water evaporate is even better. If spring water or pond water is used to water orchids, attention should be paid to testing the pH value with pH test paper. If the pH value is less than 5, alkaline substances such as lime can be added to adjust it; if the pH value is greater than 6.5, hydrochloric acid, acetic acid, citric acid, etc., can be used to adjust it. 

(3) Regardless of what material the orchid pot is made of, the bottom of the pot must have appropriate holes, and it is even better if there are several holes around the lower part of the pot wall. In short, it must allow air movement and drain water. When planting orchids, a layer of crushed brick granules or charcoal granules can be placed in the lower part of the pot to facilitate drainage and air movement. The placement of orchid pots should allow air to circulate around the bottom and walls of the pot. If conditions permit, orchid racks can be used to elevate the pots, which gives an even better effect. Growing good orchids requires suitable temperature, humidity, light, and other environmental conditions, but creating a good environment for the orchid roots is the most important link. If the orchid roots are cultivated well, ideal orchids can also be cultivated.