Why should spent mushroom substrate be treated with high heat

Spent mushroom substrate iscultivationwaste left over after growing mushrooms; its main component is cottonseed hulls. It helps loosen and aerate the mix and also contains nutrients, making it an idealorchidpotting medium. This summer, a fellow orchid grower gave me a large bag of spent mushroom substrate. After a week of baking in the hot sun, by autumn I mixed it into the potting medium at 3O% and used it. Before long, small flying insects appeared on the orchid leaves, shaped like flies, chasing one another and mating, multiplying their offspring. A few days later,the orchidswere covered in a dense black mass of them, crawling everywhere. I was truly thrown into confusion and could not think of a way to control them. Suddenly I remembered a remark from a fellow orchid grower: using spent mushroom substrateto grow orchidsbreeds earthworms. The root of the trouble must lie in the spent mushroom substrate. So I made a big effort and repotted everything again, switching to a potting medium without spent mushroom substrate. The whole uproar then subsided. Although spent mushroom substrate is disinfected by sunlight, that does not kill insect eggs; only high-heat treatment is safe and reliable. (Lao Tie)