Material for compost on farmer hand

What is Mushroom Soil Good For?

Mushroom soil can be considered a slow-release fertilizer and has many applications in your garden. Let’s break down who should use mushroom soil and where, as well as how to source it.


What is mushroom soil?

First, what is mushroom soil? Mushroom soil is sometimes called “spent mushroom substrate” or “mushroom compost” and is a substance created from the substrate of commercial mushroom growing. It can be made from a variety of things that compost into an appropriate bed for mushrooms when inoculated with mushroom spores. Some traditional farm refuse, such as cottonseed or cocoa bean hulls, meal, brewer’s grain, corn cobs, straw, and manure can create this mixture, which is then encased with peat moss and ground limestone. It is further broken down by the mushroom growth as the fungus absorbs the available nutrients. Since this substance has been used for mushrooms, it is low in readily available nutrients, but it is also slow to break down.


When to not use mushroom soil

There are a few instances where mushroom soil should not be used. First, the substance may have too high a salt content for salt-sensitive plants. Weathering the mushroom soil over the winter can help alleviate this issue.  (At Woodward, age our mushroom soil three months before selling it.)

Second, mushroom soil that has not been irradiated or treated to kill mushroom spores will likely grow a few mushrooms, so if that is undesirable for any reason, avoid mushroom soil or ensure it has been treated to kill microorganisms. The vast majority of mushroom soil is steam cleaned to kill any weeds or dangerous insects.

Finally, due to the limestone/chalk content, mushroom soil may be alkaline, so avoid using it with plants requiring a more acidic soil.


The benefits of using mushroom soil

Adding mushroom soil to potting or planting soil as a soil amendment can help with soil structure and water retention. In fact, aged mushroom soil is often used as an addition to commercial potting soil to ensure an even texture. Again, ensure that your mushroom soil has weathered for about six months to remove high salt levels if you are using it for vegetable or flower gardens that are sensitive to salt.

Using mushroom soil on a lawn before seeding will serve two purposes. First, it will help hold the appropriate amount of water to help germinate the seeds while suspended in the soil and ensure a quality growth pattern. Second, the cover of mushroom soil can help protect the nascent grass seed from birds seeking a quick snack.

As mushroom soil doesn’t contain weeds, harmful insects, or much nitrogen, it is perfect for use as mulch. It can later be mixed with compost tea and combined with soil as it breaks down, so it never needs to be removed and replaced.


Southeastern Pennsylvania, and particularly Kennett Square, is known as the mushroom capital of the United States, which gives us a ready supply of mushroom soil. Usually the mushroom substrate is only used once; since the mushrooms use most of the available nutrients during the first growth, it is more economic to remove and replace the substrate rather than to attempt to infuse additional nutrients.

Count on Woodward Landscape Supply to carry a variety of mushroom soil. We age mushroom soil on site so you can be assured when you purchase from us that it is ready to use in your own yard or garden. We can help you select the right mushroom soil and answer questions about its composition and use, or suggest other types of soil, compost, or mulch for any gardening need.

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