Mushroom soil, or Spent Mushroom Substrate, is the steam pasturized, partially composted remains of mushroom growing media after a crop of mushrooms has been harvested. While this product has some smell, it can be further composted into an odorless compost in 6 to 12 months. It can also be used directly as a mulch for vegetable or flower beds.
Mushroom soil is made from a wide variety of feedstocks that are usually proprietary to the mushroom growers creating it. Our product is sourced from a number of different growers, but since it is aggregated and aged at our facility, it tends to be fairly consistent despite the inconsistencies of the individual recipes. Raw ingredients used include wheat straw bedding containing horse manure, hay, corn cobs, cottonseed hulls, poultry manure, brewer's grain, cottonseed meal, cocoa bean hulls and gypsum, ground soybeans, seed meal, peat moss and ground limestone. Our mushroom soil can typically be requested in age ranging from fresh to approximately 6 months aged.
The ongoing decay of the Mushroom Soil can sometimes interfere with germination, so mushroom soil is not recommended when plants are to be grown from seed rather than seedlings. However, grass seed tends to be largely unaffected by this effect and can be safely planted in Screened Blend.
Additionally, due to its lime and salt content, Mushroom Soil can be detrimental to members of Ericaceae (heath family) such as rhododendrons, azaleas, camellias, blueberries and cranberries. Other woody shrubs and trees are generally similarly intolerant.