May 02

Mushroom Compost

Also known as mushroom soil, spent mushroom substrate or similar, mushroom compost is the spent growing medium from mushroom farming. Often available cheaply, mushroom compost can be used as soil conditioner or mulch.

Mushroom compost contains straw or manure, Nitrogen additives such as dried blood and chalk is added. It is high in organic matter and many nutrients such as Phosphorous and Potassium. Before use, large pieces of chalk should be removed to avoid build-up in the soil.


Because of the chalk content mushroom compost makes the soil more alkaline. It should not be overused and should not be used on acid loving species.

  • Mushroom compost makes a great mulch. It will improve the soil structure and make existing nutrients more readily available to plants. It is also weed free. A few inches should be used for mulching.
  • Mushroom compost is a useful soil conditioner, particularly if you have clay soil. It should be spread on the surface then worked in to the soil.
  • Mushroom compost is ideal for the vegetable garden or allotment. Brassicas such as cabbage, broccoli and cauliflower particularly benefit from mushroom compost.
  • It is great for dressing lawns. Ideally the compost should be cured and used with compost tea for this purpose.

Mushroom compost should not be used for pot plants. Avoid using mushroom compost near acid loving species such as rhododendrons and azaleas. It should also not be used on fruits.


  • Readily available
  • Inexpensive
  • No weeds
  • Recycled
  • High in organic matter


  • Chalk needs removing
  • May contain pesticides
  • High in salts


There are a great many uses for mushroom compost. If you can source some locally from a mushroom farm it could come in very handy as a soil conditioner or mulch. Mushroom compost usually refers to the spent growing medium however sometime unused mushroom compost is available.


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