An Introduction to Several Growing Media and Fertilizers for Orchid Cultivation

Recently, the author has received phone calls from many orchid growers in various places from time to time, and their inquiries have concentrated fairly consistently on various aspects of several growing media and fertilizers. Below, based only on the questions orchid growers asked by phone, a relatively systematic introduction is given to the sources, properties, ingredients, amounts used, preparation, effects, and many other aspects of the several growing media and fertilizers asked about, in answer to readers' questions. Spent Mushroom Substrate Spent mushroom substrate is thecultivationremaining mushroom substrate after edible fungi areorchids'scultivationmedium. Spent mushroom substrate has a wide range of sources and is easy to obtain. Edible fungus research institutes in cities and edible fungus cultivation farms run by mushroom farmers in rural areas all have large amounts of spent mushroom substrate available for use every year. There are many kinds of spent mushroom substrate, among which "shiitake soil" and "mushroom soil" are currently widely used tocultivateorchids. "Shiitake soil" is the discarded bran bag after cultivating shiitake mushrooms. The raw materials used for cultivating shiitake mushrooms are mostly mixed wood bran as the main material, and some formulas also mix in part cottonseed hulls. Practical use has shown that shiitake soil with mixed wood bran as the main material gives good results when used to grow orchids, while that mixed with cottonseed hulls gives poorer results. Shiitake soil is slightly acidic, nutritionally complete, light and loose in texture, not easily compacted, permeable to water and air, controllable in wetness and dryness, and free from the risk of fertilizer imbalance or deficiency. When shiitake soil is used to grow orchids, the root system is well developed, white and tender, with no blackening at the root tips; the orchid seedlings are sturdy, with many shoots and abundant flowers; the leaves are thick and the leaf color is deep green and glossy; the disease rate is low and there are few weeds. It is an economical growing medium with excellent results for growing orchids. Before use, shiitake soil must be crushed and exposed to the scorching sun for three days in midsummer, during which omethoate and isocarbophos are sprayed on the crushed shiitake soil to achieve insect killing and sterilization. Shiitake soil that is fully decomposed and dark brown is best. The proportion of shiitake soil in an orchid growing mix should preferably be 20%-30% (volume ratio); when plantingCymbidium goeringii, the proportion may be increased to 50%-70%. "Mushroom soil" is the discarded remaining substrate after cultivating mushrooms, and mushroom cultivation is very common in rural areas. The raw materials used for cultivating mushrooms are mainly rice straw and dry cow dung, supplemented with urea and superphosphate, and peanut cake, mixed and piled for fermentation for one month. Mushroom soil is rich in organic matter and contains all three major elements, nitrogen, phosphorus, and potassium, and its particles are small, loose, and good in drainage and aeration. Used as a base fertilizer, mushroom soil not only has sufficient fertility but also has a long fertilizer effect, does not compact, and is beneficial for absorption by orchid plants. As for the mushroom soil used to grow orchids, its processing and preparation, dosage proportion, and cultivation effects are roughly the same as those of shiitake soil. Rice Hull Charcoal Rice hull charcoal, also called rice bran ash, called long bran in the south, is a black carbonaceous substance formed by smoldering rice hulls. It belongs to a type of plant ash and can be used both as an orchid growing medium and as a fertilizer. The composition of plant ash is extremely complex, containing various ash elements found in crop plants, such as potassium, calcium, phosphorus, magnesium, sulfur, iron, and silicon, among which potassium and calcium are the most abundant, followed by phosphorus. From the perspective of fertilizer, it is often used as a source of potassium fertilizer, but for crop nutrition it is not only potassium, but also phosphorus and other elements that play a role. Rice hull charcoal is alkaline and rich in potassium, phosphorus, calcium, and other nutrient elements, containing 5%-10% potassium and 1%-4% phosphorus, and it has a quick fertilizer effect. Mixing a certain amount of rice hull charcoal into an orchid growing mix can promote photosynthesis in orchid plants, benefit the synthesis of carbohydrates and the growth of orchid roots, and also prevent orchid plants from lodging and improve resistance topests and diseases. Rice hull charcoal has good air permeability and water absorption, can improve soil structure, and raise the temperature of the potting soil. When fresh, rice hull charcoal is alkaline (pH 8.5-9); after being burned, it should be left for many days or exposed to sun and rain for a period of time until it becomes neutral before use. The proportion of rice hull charcoal mixed into an orchid growing mix should preferably be 10%-20% (volume ratio). If it is used to cultivate variegated-leaf orchids, the proportion may be increased to 20%-30%; soil that is somewhat alkaline is beneficial for preserving and enhancing the variegation of variegated-leaf orchids. The burning of rice hull charcoal is rather particular. A relatively large amount of rice hulls can be piled into a heap, using the method by which mountain people burn fired soil, and allowed to smolder slowly; the best result is a black carbonaceous substance that keeps the original shape of the rice hulls. If it is burned too thoroughly and becomes white ash, the phosphorus and potassium nutrients it contains are greatly reduced. Rice Washing Water Rice washing water is the water left after washing rice; in some areas it is called rice soak water. It has a wide range of sources and is easy to obtain, but rice washing water with oily matter must not be used. Rice washing water is weakly acidic, contains relatively much potassium, followed by phosphorus, and also contains certain trace elements, making it a good phosphorus-potassium fertilizer. Wateringorchidswith fermented rice washing water can promote the growth and development of orchid plants, making the orchid plants green in leaf, sturdy in seedling, fragrant in flower, and fast in propagation, and free frompests and diseases. Rice washing water generally needs to be fermented for one week before use; when fermented in the high-temperature summer season, it decomposes relatively quickly. As for the fermentation method, it can be naturally decomposed in the open air, or fermented sealed in a bucket with a lid. With the "natural decomposition method," because the container is not sealed with a lid, the odor produced by fermentation during the decomposition process will spread out from the bucket and drift away with the wind, polluting the environment. With the "sealed bucket with lid method," there is no such drawback. When using fermented rice washing water to water orchids, "better too dilute than too concentrated"; generally, 1 part rice washing water mixed with 2 parts clear water is suitable. From February to May, water the roots with fermented rice washing water once every 15 days; from June to October, water the roots once every 3-5 days; from November to January of the following year, when orchids are in the winter dormancy period, water the roots once every 10 days. (Longyan, Fujian - Zhang Bingfu)