Spent Mushroom Substrate (SMS) (or spent mushroom compost) is a useful source of organic matter, which can supplement garden compost. Mushroom substrate is composed of chopped wheat straw, poultry manure, horse manure and gypsum, which are mixed and composted under controlled conditions, and then used as a growth substrate for mushroom production. SMS is an excellent soil conditioner, a source of organic matter and a valuable source of major and minor nutrients (see table below):
SMS contains around 8.0 kg N/tonne on average, with the majority of N in an organic form, which is slowly released over time. SMS also contains essential micronutrients such as Sulphur, Magnesium, Manganese, Copper and Boron. The fibre from the straw improves soil structure, which can improve soil fertility. There is significant environmental pressure to reduce the use of peat in gardening and it can be difficult to find another source of organic matter, however, SMS is readily available as an excellent replacement.
If you are interested in accessing spent mushroom substrate, contact your nearest mushroom grower or mushroom producer organisation (Commercial Mushroom Producers (CMP), Northway or Farm Fresh Produce). Spent mushroom compost has valuable levels of nutrients and organic matter.
