Editing Spent mushroom compost (section)

==Background==
It is readily available (bagged, at nursery suppliers), and its formulation generally consists of a combination of [[wheat]] straw, dried blood, [[horse manure]] and ground chalk, composted together. It is an excellent source of [[humus]], although much of its [[nitrogen]] content will have been used up by the composting and growing mushrooms. It remains, however, a good source of general nutrients (1-2% [[Nitrogen|N]], 0.2% [[Phosphorus|P]], 1.3% [[Potassium|K]] plus a full range of [[trace element]]s), as well as a useful [[soil conditioner]].<ref>[https://homesteadgardener.com/mushroom-compost-in-raised-beds/ How to use mushroom compost in raised beds]</ref> However, due to its [[chalk]] 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 [[Soil pH|pH]] levels.<ref>{{Cite book|title=Vegetable Gardening: Growing and Harvesting Vegetables
|first=Steve|last= Bradley|publisher=Murdoch Books|year=2004|isbn=1-74045-519-3}}</ref>

Mushroom compost may also contain [[pesticide]] residues, particularly [[organochloride]]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 gardening|organic gardener]] must be careful regarding the sourcing of mushroom compost; if in doubt, samples can be analyzed for contamination &ndash; in the [[United Kingdom|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.<ref>[http://green-change.com/2009/01/17/growing-mushrooms-from-mushroom-compost/ How to grow mushrooms in spent mushroom compost before using in garden beds]</ref>