Mushroom Compost Advantages What It Is And Why To Use It

How to Make Mushroom Soil

mushroom compost
Mushroom Compost By Daryl Mitchell

Mushroom compost generally gets labeled as SMC or SMS (spent mushroom compost or spent mushroom substrate) when purchasing it from the store.

It can get used as a soil amendment, but you need to use it cautiously because of its high soluble salt levels.

The salt levels can be high enough to harm young seedlings, kill germinating seeds, and damage any salt-sensitive plants.

SMC has shown to be a good material if you want to improve the soil structure of tilled soils and increase dry matter production in grassland soils.[7]

It commonly gets added to help improve clay soil structure.[10]

What Does Mushroom Compost Do To The Soil?

Mushroom compost will enrich your soil by supplying all macro and micronutrients to help you grow healthy plants.

The water holding capacity of your soil gets increased, helping to reduce the amount of water you need to provide and making your garden more drought resistant.

You can also increase your soil's microbial activity and fertility while reducing your need for using fertilizers later in the season.

It works very well in helping to amend clay-like soils over time.

It would be best if you did not use it to replace all of your standard compost completely. It can hold too much water for your soil, causing it to become waterlogged and problematic to your plant's health.[5]

Using Mushrooms As Fertilizer

When you blend in mushroom compost with your soil, the nutrients act as a slow-release fertilizer.

When mixing in with your soil, it is most common to use between 25 to 50 percent of mushroom compost to medium.

You can also add it as a top dress layer for your lawn. Over time it will work its way down into your soil, adding a little boost of nutrients to your grass.

Mushroom Compost For Vegetable Garden

When you add the compost to your vegetable garden or flower beds, you should till three inches of it into the top six inches of your soil.

It gives the best rest on soil beds that are relatively dry or sandy.[8]

Mushroom Compost As Mulch

While mushroom compost can also get used as a mulch, you should only use it around perennials, trees, and shrubs.

Do not use it as a mulch if you have members of the heath family (rhododendrons, azaleas, camellias) since they can end up getting hurt from the higher salt contents contained in it.

Mushroom Compost Acidic or Alkaline

It has a neutral pH level between pH6 and pH7.

Mushroom Compost Should Be Your Choice For

  • Growing flowering plants (it is beneficial for almost all of them)
  • Growing vegetables
  • Growing herbs
  • Trees, including fruit trees
  • Shrubs
  • Newly established lawns

Avoid Mushroom Compost If You Grow

  • Native plants
  • Fruit Bushes
  • Acid-loving plants like heath family (magnolia, camellias, azaleas, heathers, or rhododendrons)

How to make Mushroom Compost

You do not make mushroom compost by composting mushrooms. But instead, it is the soil used to grow the mushrooms that you will use to make mushroom compost.

One of the most popular commercial blends of the mushroom substrate is wheat straw, gypsum, and horse or chicken manure.[5]

Check out the video below on how you can make your mushroom compost at home.

You must identify any mushrooms in your garden before eating.

Step 1

After you have removed your edible mushrooms, mix the soil, straw, manure, and mushroom bacteria up together nicely.

Move the soil mixture to create a large pile, make sure it gets lots of sunlight, and is in a location you can let it sit in for several weeks. It needs lots of sunlight so you can perform the hot compost process in the next step.

Step 2

Add more moisture regularly by spraying the pile down with a hose or adding buckets of water.

Now you will perform a hot compost process for a minimum of 2 weeks. You are trying to get the pile to reach at least 160 degrees Fahrenheit. At this temperature, any weed seeds and harmful bacteria will get eliminated from within your compost.

Every one to two days, you need to turn over the compost letting air get introduced back into the compost pile. It will also allow the more extensive exterior materials to break down faster.

Step 3

After you complete the hot composting process, you need to let the compost age and cure further.

By curing the pile, you allow low-temperature microbes to begin to flourish. They will continue breaking down the organic material. It also will enable earthworms and other larger organisms which don’t tolerate high heat to move back into the compost.

Move your compost to a shady area as we don't want the compost to reach high heat for this portion of the process.

You do not need to turn over the compost while curing. Keep it moist and allow it to sit for a couple more weeks. Your compost should gradually turn a darker brown while curing.

At this point, you now have mushroom compost you can add to your garden or flower beds.

Mushroom Compost Nutrients

Primary Macro Nutrients

Fresh mushroom compost is an excellent source of organic matter, with many different plant nutrients that will get slowly released over time.

Carbon to Nitrogen ratio.

All of these nutrient values get based on fresh mushroom compost. But over time, the nutrient value of your mushroom compost will slowly get reduced.

The average C:N ratio for fresh mushroom compost is ideal at 13:1.

The carbon relative to nitrogen indicates the level of nitrogen available to your plant's growth. Suitable composts will have an ideal ratio of anywhere between 10:1 to 15:1 and never above 30:1.

The average NPK value of mushroom compost is 1.1-0.7-1.3. Thus, the NPK ratio is similar to most other compost, with an average ratio value of 1-1-1.[1]

Mushroom compost has a higher calcium level at around 2.3% but should not be an issue for most soils.

Most nitrogen is available in organic form, with a small percentage obtainable in the ammonium form.[2] Most of the nitrogen in organic form allows it to get released to your plants over time slowly.[3]

Secondary Macronutrients

Calcium (Ca), magnesium (Mg), and sulfur (S) are secondary macronutrients required by most plants but in lower quantities than N-P-K.

Calcium will support the membrane structure and function of your plants.

Magnesium is required for your plants to have proper photosynthesis and is a central component in chlorophyll.

Sulfur is the primary macronutrient that will support the amino acid synthesis of your plant's production.

The average Ca-Mg-S from fresh mushroom compost is 2.3%-0.4%-0.9%.


Iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) are the primary micronutrients.

Mushroom compost provides all of these nutrients in a low average range.

The average Fe-Mn-Cu-Zn provided by your mushroom compost is 0.2%-0.4%-0.01%-0.01%.

Lab tests show that fears of excessive amounts of zinc do not appear to be present in high enough quantities to cause toxicity.

These micronutrients get required for chlorophyll synthesis (Fe), formation of oxygen during photosynthesis (Mn), cellular respiration (Cu), and enzyme functions (Zn).[1]

Advantages Disadvantages Mushroom Compost

The Benefits of Mushroom Compost

  • Inexpensive
  • Enriches the soil and supplies nutrients
  • Increases the water-holding capacity
  • Eco-Friendly
  • Attracts earthworms
  • It helps to reduce landfill waste by reusing the soil.

Disadvantages of Mushroom Compost

  • Rich in soluble salts
  • Can Cause Water Logging
  • Can Cause Rot or Fungal Infections
  • It does not contain beneficial microorganisms.
  • Possibly contain chemical residues.


Mushroom compost can be a helpful addition to your garden if you want to increase your soil's water retention while providing some extra slow-release nutrients.

While adding it to your garden can help increase your soil's biodiversity, the mushroom compost you purchase has been sterilized and no longer contains healthy soil microbes.

Many producers of mushroom compost use insecticides and antifungals while the mushrooms are growing.

If you do not see it labeled as certified organic, it is best to assume the chemical residues may be in the compost.

Similar Articles

Biochar Fertilizer
Green Manure For Clay Soil
Everything About Superphosphate Fertilizer