Mushroom Compost: 3 Ways to Use Mushroom Compost

Mushroom compost is a mixture of organic matter for mushroom growing. After mushroom growers use the compost and it is spent of mushroom-supporting nutrients, the compost is often resold or repurposed for regular garden compost needs. While not as nutrient-rich as traditional compost, spent mushroom substrate retains water and provides nutrition for plants.

Mushroom compost can comprise a variety of materials, including peat moss, chopped straw—usually rye, wheat straw, or horse bedding straw with horse manure—gypsum, chicken manure, urea, potash, and ammonium nitrate. Mixtures may also include cotton seed hulls, winery grape crushings, and soybean meal.

You can use spent mushroom compost to enrich your soil, boost soil quality, and break down dense soil:

1. 1. Use mushroom compost as a soil amendment. You can use mushroom compost to add organic materials to your garden soil. You can also enrich your vegetable gardens, raised beds, flower gardens, new lawn, or orchard with the substrate. Top-dress the soil with a thin layer of mushroom compost for a soil booster. It is a slow-release fertilizer, meaning that it’s relatively low nutritional value adds to the soil slowly over time.
2. 2. Substitute mushroom compost for mulch. Trees and shrubs can also benefit from the addition of mushroom compost. You can use the compost like mulch. Place it around the trunk of a tree for increased water retention and to boost the overall quality of the soil.
3. 3. Use mushroom compost to break down clay soil. Mushroom compost is good at breaking down dense, clay-like soils, because the straw content will help break up this dense material.
4. 4. Use mushroom compost to grow mushrooms. By the time mushroom compost is commercially sold, it is no longer able to produce mushrooms on a desired economic scale. If left in a reasonably stable environment with adequate moisture (covering it with a layer of peat can help), you can grow another crop of mushrooms at home. The nutrients necessary for mushroom growth—protein, starches, lignin, fats, nitrogen—are still present, if in smaller quantities, from the organic matter in the compost. Since the mycelium is present, all it takes is time and care for a new crop of fruiting heads to appear.

When using freshly purchased mushroom compost, it can be helpful to treat it with compost tea, or mix it with greater amounts of regular compost, to reintroduce microorganisms. Many manufacturers sterilize their mushroom compost before sale, eliminating the beneficial microorganisms that help make high-quality soil.

Mushroom compost contains soluble salts that can be harmful to acid-loving plants such as magnolias, camellias, azaleas, rhododendrons, and blueberry bushes. However, there are ways of treating the mushroom compost so that it will be suitable for them. Vermicomposting your mushroom compost, which is a process of composting that uses live worms, is one method. You can also leave your compost out in the open air, allowing it to further decompose. Each of these methods will leach out high salt levels and add beneficial microorganisms to the compost to support plant growth.

Grow your own garden with Ron Finley, the self-described "Gangster Gardener." Get the MasterClass Annual Membership and learn how to cultivate fresh herbs and vegetables, keep your house plants alive, and use compost to make your community—and the world—a better place.