What plants like mushroom compost?

Most garden crops benefits from mushroom compost as a soil amendment, especially plants that tolerate higher salt content and benefit from additional calcium, such as tomatoes. Make sure to only use well-aged mushroom soil around rhododendrons, azaleas, camellias, and other members of the Heath family, (Ericaceae) because the high salt content can harm the plants.

Can you plant directly in mushroom compost?

You should not plant in mushroom compost as the only growth medium but always work it into the soil. If you follow this rule, it depends whether you can plant directly in the amended soil. Tender seedlings and seeds are sensitive to the high salt levels in mushroom compost so it’s better to wait until the plants are established before working some mushroom soil into the soil around the plants.

Can you use too much mushroom compost?

As with all soil amendments, overdoing it is harmful. Don’t exceed the recommended amount of a 1- to 3-inch layer or three to nine cubic yards per 1,000 square feet.

Gardening Gardening Basics Garden Tasks

What Is Mushroom Compost and Why Use It

How Mushroom Soil Can Benefit Your Plants

By

Nadia Hassani

Updated on 02/27/24

Reviewed by

Barbara Gillette

How Mushroom Compost Is Made

When the substrate in which mushrooms are grown is no longer suitable for mushroom-growing, it is still valuable for gardeners.

Mushroom substrate contains hay, straw, poultry or horse manure, crop residue such as corn cobs and cocoa shells. The exact composition of the growth substrate varies from grower to grower. The substrate is composted for about 30 days at a temperature of 160 degrees F to kill any weed seeds, pests, or disease pathogens. Additionally, it is steam-pasteurized at about 140 degrees F to kill any pests and pathogens that could cause surface diseases. Then the medium is inoculated with mushroom spawn, or mycelium, and covered with a layer of sphagnum moss and ground limestone to support the mushroom growth.

After mushrooms have been harvested for about three to four weeks, the medium’s ability to sustain mushroom growth is exhausted and it is replaced with fresh mushroom soil for a new batch of
mushrooms. The substrate is then sold as bags or bulk, often labelled as SMC (Spent Mushroom Compost) or SMS (Spent Mushroom Substrate).

The Pros and Cons of Mushroom Compost

Mushroom compost is not an cure-all for your garden soil. It has benefits and disadvantages.

Pros	Cons
Supplies macronutrients (nitrogen, phosphorous, potassium), and micronutrients (calcium, magnesium, iron) to the soil	Nutrient composition varies depending on the materials used
High in organic matter, which increases the water-holding capacity of the soil, boosts the activity of beneficial soil microbes	High in soluble salts and other nutrients that can kill germinating seeds, harm young seedlings, and cause damage to salt-sensitive plants
Improves the structure of clay and compacted soils, which increases drainage
Suitable for most garden plants, both edibles and ornamentals	Pricy and not readily available
High levels of calcium which benefits some crops, such as tomatoes	High calcium content can increase the soil pH and make it too alkaline

Mushroom Compost vs. Regular Compost

Mushroom compost and regular compost are not interchangeable due to key differences between the two.

All compost varies in composition, unlike commercial fertilizer, where the label gives a detailed analysis of the nutrients. Mushroom compost has already been used as a growing medium which means it generally contains less nitrogen than regular compost. It may be a good choice for soil already rich in nitrogen since excess nitrogen can lead to overgrowth of foliage and stunted roots.

Mushroom soil also contains more calcium than regular compost due to the addition of chalk. Plants like tomatoes do well in a calcium-rich soil which helps tamp down blossom-end rot. However, calcium increases the soil pH level which is problematic for plants like blueberries that need acidic soil.

Mushroom Compost vs. Manure

Mushroom compost and manure are two different soil amendments, not only in their composition but also in their use.

Mushroom compost contains a wide range of organic materials, including horse manure, which have undergone a sanitization process before the mixture is used for growing mushrooms. It is less dense and lighter than manure and ready to be spread in the garden. Manure, on the other hand, regardless of the type (cow, horse, or poultry), only contains animal dung and straw or sawdust from the animal’s bedding or litter areas. Fresh manure is very high in nitrogen and needs to mature before being used, otherwise it will burn the plants.

Fresh mushroom compost has an average of 6.6 so it falls right into the ideal pH range for most crops between 6.0 and 7.0. Manure has a higher pH (above 7.0) and makes soil more alkaline.

Tip

If you are an organic gardener and want to make sure the mushroom source is also fully organic, select mushroom compost from certified organic mushroom farms that practice organic fertilization, pest, and fungal disease management.

When and How to Use Mushroom Compost

Most mushroom compost sold in the trade has been aged or cured but if you happen to buy mushroom compost that is still fresh, it needs curing before you add it to your soil. Purchase fresh material in fall, winter, or early spring to give it ample time to sit and cure before planting or spreading it around plants. Rain and snowfall leach excess salts from the substrate and the already low pesticide residue that might be in the substrate from the mushroom growing has time to decompose.

Topdressing lawn — Dorin_S / Getty Images

Aged, cured mushroom compost can be applied any time in the spring or summer. Application is most effective when the soil is fairly dry, which avoids compacting the soil while tilling in amendments.

Aged mushroom compost, either worked into the soil or spread around the base as mulch, can be added to a wide range of plants, including:

Lawns, also as a top-dressing for newly seeded lawns
Vegetable gardens
Orchards
Perennials, trees, and shrubs
Container plants

For flower beds and vegetable gardens, evenly spread one to three inches of mushroom compost over the surface and till it into the top six inches of soil. For container plants, mix about one quarter volume of aged mushroom compost with three-quarters of potting medium.

The 8 Best Composters of 2024, Tested and Reviewed

FAQ

What plants like mushroom compost?

Most garden crops benefits from mushroom compost as a soil amendment, especially plants that tolerate higher salt content and benefit from additional calcium, such as tomatoes. Make sure to only use well-aged mushroom soil around rhododendrons, azaleas, camellias, and other members of the Heath family, (Ericaceae) because the high salt content can harm the plants.
Can you plant directly in mushroom compost?

You should not plant in mushroom compost as the only growth medium but always work it into the soil. If you follow this rule, it depends whether you can plant directly in the amended soil. Tender seedlings and seeds are sensitive to the high salt levels in mushroom compost so it’s better to wait until the plants are established before working some mushroom soil into the soil around the plants.
Can you use too much mushroom compost?

As with all soil amendments, overdoing it is harmful. Don’t exceed the recommended amount of a 1- to 3-inch layer or three to nine cubic yards per 1,000 square feet.

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

What Is Mushroom Compost? Oregon State University Extension Service.
Does Adding Manure Lower or Raise Soil pH? University of Florida.
Spent Mushroom Substrate. Penn State Extension.
Mushroom Compost FAQ. American Mushroom Institute.