Organic mushroom compost has become an increasingly popular soil amendment for home gardeners and small-scale farmers. This dark, rich material provides a natural way to add nutrients and organic matter to enrich garden beds and planting holes. Understanding what mushroom compost is, where it comes from, and how to use it properly can help you take advantage of the benefits it offers.
What is Mushroom Compost?
Mushroom compost is a byproduct of the commercial mushroom growing process. Mushrooms are grown indoors under controlled conditions in large stacks of organic material called “substrate.” This substrate is typically made from materials like straw, manure, peat moss, and ground corncobs. After the mushrooms are harvested, the spent substrate is pasteurized to kill any pathogens. This leftover material, known as “mushroom compost” is then sold as a soil amendment.
The main ingredients in mushroom compost vary between producers, but the compost will generally contain:
- Partially decomposed straw and hay
- Manure from horses, chickens, or other livestock
- Gypsum
- Vermiculite or perlite
- Cocoa shells
- Peat moss
These organic materials give mushroom compost some great properties for enriching garden soil.
Benefits of Using Mushroom Compost
Several key benefits make mushroom compost a valuable addition to the home garden:
1. Rich in Organic Matter
Mushroom compost introduces large amounts of organic material into the soil. Organic matter improves soil structure and moisture retention. It also feeds important soil organisms like earthworms, fungi, and bacteria. These microbes convert organic matter into available nutrients for plant roots.
2. Nutrient Content
In the process of decomposing the organic ingredients, mushroom compost acquires a diversity of plant nutrients. It contains nitrogen, phosphorus, potassium, calcium, and magnesium. Micronutrients like iron, zinc, manganese and copper are also present. These nutrients are released slowly over time.
3. Soil pH Buffer
Mushroom compost has a neutral pH around 6.5-7.5. This makes it useful for moderating soil that is too acidic or alkaline. By bringing soil pH into the optimal range, nutrients become more available for plant uptake.
4. Improves Soil Structure
The organic matter in mushroom compost feeds soil microbes and bind particles into crumbs. This creates a loose, crumbly soil texture ideal for root growth and drainage. Heavy clay soils become lighter and easier to work.
5. Holds Moisture
The increased soil organic matter acts like a sponge to retain moisture. Compost allows the soil to hold more water available to plant roots. This helps reduce watering requirements.
6. Promotes Healthy Root Growth
The nutrients, organic matter, and neutral pH create ideal conditions for root development. Mushroom compost encourages extensive root systems with lots of fine feeder roots.
7. Suppress Plant Diseases
Some research indicates mushroom compost can suppress certain soil-borne plant diseases like fungal wilts and root rots.
8. Environmentally Friendly
Using mushroom compost keeps this waste material out of landfills and takes advantage of its value as a soil amendment. It’s a sustainable way to boost your garden soil using recycled organic resources.
How to Use Mushroom Compost in Your Garden
Mushroom compost can be applied in several different ways depending on your goals:
Amending Garden Beds
To enrich the soil of a whole garden bed, apply a 2-4 inch layer of mushroom compost over the bed and mix it into the top 6-12 inches of native soil. This will improve the soil structure and nutrient content of the entire bed before planting.
Adding to Planting Holes
When transplanting plants or sowing large seeds like beans, add a few shovelfuls of mushroom compost to the bottom of the planting hole. Place the plant or seeds on top of the compost and backfill the hole with native soil. This gives plants an enriched root zone to establish quickly.
Topdressing Lawns
To improve the health of lawns, spread mushroom compost in a thin layer over the grass, about 1/4-1/2 inch deep. The compost nutrients will feed slowly into the soil and roots. It also encourages earthworms and beneficial soil microbes.
Mulching
Use mushroom compost as an organic mulch around annuals, perennials, trees and shrubs. Spread 2-3 inches evenly over the soil surface. It will conserve moisture while releasing nutrients. Reapply annually.
Potting Mix
Mix mushroom compost into potting soils and soilless media for containers and raised beds. Blend it one part compost to two parts potting soil or peat-based mix. This provides nutrients and helps aerate the media.
Sourcing High Quality Mushroom Compost
Not all mushroom composts are created equal when it comes to quality. Here are some tips for finding a high-grade compost source:
- Ask garden centers about their mushroom compost ingredients and production process
- Look for compost made from organic agricultural materials, not municipal waste
- Compost should have an earthy smell, not ammonia odors, and be free of visible contaminants
- Find producers using sustainable practices and clean raw materials from reputable sources
- The compost pile should be properly cured, not fresh—it will appear dark and crumbly when squeezed
- Ask if lab testing is done check for nutrient content and contaminant levels
- Purchase from local compost producers to support small businesses and reduce transport miles
Using Mushroom Compost Safely
Mushroom compost made from clean organic materials is very safe to handle and use in the garden. A few common sense precautions will ensure you avoid any potential downsides:
- Wear gloves and a dust mask when handling dry mushroom compost, as with any compost
- Avoid inhaling dust by wetting down compost piles before spreading
- Wash produce thoroughly if compost has been applied recently
- Don’t pile compost directly against plant stems or trunks
- Test compost before applying to edible crops if you have any uncertainty about its production process
- Introduce compost gradually to allow the soil ecosystem to adapt and avoid salt stress
Troubleshooting Problems with Mushroom Compost
When used properly, mushroom compost offers many benefits. But occasionally gardeners report issues after applying it. Here are some potential problems and solutions:
Salty or Alkaline Soil
High soluble salt levels in mushroom compost can build up in soil over time and affect plant growth. Test soil pH and salts after repeated compost applications. Flush soils by heavy watering to remove excess salts if needed.
Nutrient Deficiencies
The nutrients in mushroom compost are not always complete. Deficiencies of nitrogen, potassium or iron can occur. Test soil and amend accordingly to supplement any nutrients lacking.
Odor Issues
Some mushroom compost may contain high levels of ammonia that cause odors. This indicates immature compost. Allow material to cure fully before application, and water thoroughly to dilute ammonia.
Weed Seeds
Mushroom compost is not sterile and may contain weed seeds if raw materials were not composted fully. Heat-treat compost or purchase from suppliers using weed-free raw materials.
Heavy Metal Contamination
Mushroom compost made from biosolid wastes may contain heavy metals. Source compost only from clean agricultural materials, not municipal wastes. Require lab tests for contaminants.
Finding the Best Mushroom Compost Sources
Mushroom compost can be purchased bagged or in bulk from garden centers, landscape suppliers, nurseries, or directly from mushroom farms. Here are some top national brands to look for:
- Black Gold Mushroom Compost – Made from agricultural materials under controlled conditions producing a consistent, high-quality product.
- Espoma Organic Mushroom Compost – An OMRI certified organic mushroom compost ideal for organic gardening. Made from peat moss, cocoa fiber, and other natural ingredients.
- Lambert Peat Moss Mushroom Compost – A reliable compost made by a leading peat moss producer in Canada with organic agricultural inputs.
You may also have access to excellent local and regional mushroom compost producers in your area. Check with gardening neighbors for recommendations on local mushroom compost sources. Some small farms sell compost directly to consumers.
Mushroom Compost FAQs
Does mushroom compost go bad?
Properly cured mushroom compost does not really go bad, but it will decompose faster if left exposed to rain and sun. Store unused compost in a shed or covered area to preserve its nutrients.
How long does mushroom compost last?
The nutrients in mushroom compost will continue releasing for 2-3 years in the soil. However, it’s best to reapply annually in garden beds or around perennials.
Can you use too much mushroom compost?
Over-application of mushroom compost can potentially create high salinity. Limit initial use to 25-50% of total soil volume, and monitor soil pH and salt levels.
Is mushroom compost acidic or alkaline?
Most mushroom compost has a neutral pH around 6.5-7.5. However, prolonged exposure to water may increase acidity over time. Test pH periodically with repeated applications.
Does mushroom compost attract mushrooms?
Mushroom mycelium is killed off during commercial compost production, so the compost itself will not generate mushrooms. However, it supplies ideal nutrition if spores seed the compost.
Get the Most From Organic Mushroom Compost
Mushroom compost is a wonderful way to boost soil health, add organic matter, and provide nutrients for your garden plants. Sourcing high-quality mushroom compost and using it properly reduces any potential risks. With the right organic materials and sustainable production practices, mushroom compost offers an organic, environmentally-friendly means to take your garden soils to the next level.