Organic Brands Mushroom Compost This is a recycled specialty soil that was used to grow mushrooms. Because mushrooms are such a delicate crop, the soil is used only once. Then, it is sterilized and composted. This rich growing medium is perfect for vegetable and flower gardens, trees and shrubs or topdressing existing lawns. It contains fibrous peat, gypsum, dolomite, crushed feathers, cottonseed meal, straw and other ingredients known only to the mushroom farm’s chief grower. It will store indefinitely. Available in 40 lb. bags.