Spent mushroom substrate is the composted organic material remaining after a crop of mushrooms is harvested. Mushrooms are grown in a mixture of natural products, including horse-bedded straw (straw from horse stables), hay, poultry manure, ground corn cobs, cottonseed hulls, gypsum, and other substances. This mixture is composted in piles or ricks, creating a dark brown, fibrous, and pliable organic growing media. When the composting process is complete, the media is brought into mushroom houses where it is placed into beds or trays and used as a substrate for growing mushrooms. After the mushrooms are harvested, the “spent” substrate is removed from the houses and pasteurized with steam to kill insects, pathogens, and mushroom remnants.
If you are trying to improve the quality of turf growing in poor or marginal soils, consider using spent mushroom substrate (SMS) as a soil amendment. Spent mushroom substrate (sometimes called mushroom soil, recycled mushroom compost, or mushroom compost) can improve the structure of clay soils, reduce surface crusting and compaction, promote drainage, increase microbial activity, and provide nutrients to turfgrasses. These improvements promote faster turf establishment, improved turf density and color, increased rooting, and less need for fertilizer and irrigation.
Spent mushroom substrate production sites are located near areas of intensive turf use, providing a readily-available source of organic matter. When considering costs, keep in mind that SMS may produce better soil and turf than equal or greater amounts of topsoil.