Spent mushroom compost is the residual compost waste generated by the mushroom production industry.

Background

It is readily available (bagged, at nursery suppliers), and its formulation generally consists of a combination of

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

straw, dried blood,

horse manure Manure is organic matter that is used as organic fertilizer in agriculture. Most manure consists of animal feces; other sources include compost and green manure. Manures contribute to the fertility of soil by adding organic matter and nu ...

and ground chalk, composted together. It is an excellent source of humus, although much of its

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

content will have been used up by the composting and growing mushrooms. It remains, however, a good source of general nutrients (0.7% N, 0.3% P, 0.3% K plus a full range of

trace element __NOTOC__ A trace element, also called minor element, is a chemical element whose concentration (or other measure of amount) is very low (a "trace amount"). They are classified into two groups: essential and non-essential. Essential trace elements ...

s), as well as a useful soil conditioner. However, due to its

chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...

content, it may be alkaline, and should not be used on acid-loving plants, nor should it be applied too frequently, as it will overly raise the soil's pH levels. Mushroom compost may also contain pesticide residues, particularly

organochloride An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class (alkanes with one or more hydrogens substituted by chlo ...

s used against the fungus gnat. If the compost pile was stored outside, it may contain grubs or other insects attracted to decaying matter. Chemicals may also have been used to treat the straw, and also to sterilize the compost. Therefore, the

organic gardener The following outline is provided as an overview of and topical guide to organic gardening and farming: Organic farming – alternative agricultural system that relies on fertilizers of organic origin such as compost, manure, green manur ...

must be careful regarding the sourcing of mushroom compost; if in doubt, samples can be analyzed for contamination – in the UK, the Department for Environment, Food and Rural Affairs is able to advise regarding this issue. Commercially available 'spent' mushroom compost is not always truly spent. It is sold by mushroom farms when it is no longer producing commercially viable yields of mushrooms. It can be used to grow further smaller crops of mushrooms before final use on the garden.How to grow mushrooms in spent mushroom compost before using in garden beds
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References

{{Permaculture Soil improvers Composting Organic gardening Permaculture Sustainable gardening