Last Updated on September 23, 2024 by Amit

Mushroom compost is an exceptional addition to gardening practices. It’s a great soil builder and highly effective in retaining moisture and breaking down dense, clay-like soils. This guide will cover everything you need to know about mushroom compost, from what it is to how to use it, and even how to make it at home.

What Is Mushroom Compost?

Contrary to what many may think, mushroom compost isn’t made from mushrooms. Instead, it refers to the material or substrate used to grow mushrooms. This substrate typically consists of wheat straw, gypsum, and manure, usually from horses or chickens. While this might sound odd, it’s a beneficial garden product.

Mushroom compost comes in various forms, and understanding them can help you better utilize this fantastic soil amendment.

Types of Mushroom Compost

1. Mushroom Substrate

Mushroom substrate refers to the mixture used in commercial mushroom farming. This substrate is generally a combination of wheat straw, gypsum, and chicken or horse manure. The straw is soaked, shredded, and mixed with manure and gypsum. The mixture then undergoes a composting process, where it is turned and watered over a few weeks. This hot composting process helps break down the materials and prepares them for growing mushrooms.

Once composted and sterilized, this substrate can grow mushrooms commercially. Although this form of compost is nutrient-dense, it primarily serves as a medium for growing mushrooms and not for general gardening.

2. Spent Mushroom Substrate

The spent mushroom substrate is the most common compost sold in garden centers. Once mushrooms have been cultivated in the substrate and are no longer viable for mushroom farming, they are sold as compost. While this compost may be lower in nutrients due to the mushrooms consuming much nitrogen, it remains a fantastic soil amendment, particularly for loosening clay soils and improving water retention.

This type of compost is often used in lawns and raised beds as it helps enhance soil structure. Though spent mushroom compost can occasionally still produce mushrooms, they are generally harmless. However, avoid consuming these mushrooms, as they may not be edible.

3. Alternative Mushroom Compost

In addition to wheat straw and manure, mushrooms can be grown on other substrates like coffee grounds, hardwood dust, or coconut coir. These alternatives are popular among home mushroom growers and, once the mushroom cultivation process has been completed, make excellent garden composts.

Uses of Mushroom Compost in the Garden

Mushroom compost is not a direct substitute for soil but makes an excellent soil amendment. A good mix is about 25% mushroom compost to 75% soil. This combination helps improve soil texture and water retention. While mushroom compost is not high in immediate nutrients, it acts as a slow-release fertilizer with an NPK ratio of approximately 2-1-1.

Mushroom compost can also be used as mulch for gardens or as a top-dress for lawns. When fresh, it helps to prevent weeds from taking root. Over time, it improves soil quality as it decomposes, making it an excellent long-term soil improver.

Fertilizing Power of Mushroom Compost

Although not as nutrient-dense as traditional compost, mushroom compost provides a slow-release nitrogen, phosphorus, and potassium source. Additionally, it is low in heavy metals and helps improve soil pH by bringing it to a more neutral level of around 6.6.

Caution: Don’t Overuse

While mushroom compost is beneficial, it is essential to avoid overuse. Too much mushroom compost can result in waterlogged soils, especially in areas with poor drainage. Mixing it with other composts or adding compost tea can introduce beneficial microorganisms to your soil, improving its health.

Making Mushroom Compost at Home

Making mushroom compost at home can be a rewarding experience, especially if you enjoy DIY gardening projects. The process involves creating a hot compost pile and curing it until it turns dark brown and crumbly.

The Composting Process

1. Materials: Start with a mix of straw, manure, and a nitrogen-rich component like coffee grounds.
2. Hot Composting: Pile the materials and turn them regularly to introduce air. Keep the pile moist and ensure that the internal temperature reaches 160°F for a few days to kill off weed seeds and harmful bacteria.
3. Aging and Curing: After two weeks, transfer the compost to another pile for curing. Over time, the compost will darken and break down further, making it ready for use.

Pasteurization and Sterilization

If you plan on growing mushrooms in the compost, it’s crucial to pasteurize or sterilize it to eliminate any harmful microorganisms. Pasteurization involves soaking the compost in hot water (about 160°F) for 1-1.5 hours, while sterilization requires using a pressure cooker at 15 PSI for 2.5 hours. These steps ensure the compost is free from bacteria and mold, making it ready for mushroom growth.

FAQ on Mushroom Compost

1. What is Mushroom Compost?

Mushroom compost is an organic material used as a soil amendment, made from the substrate left after commercial mushroom farming. It typically consists of wheat straw, gypsum, and manure.

2. Is Mushroom Compost Good for Plants?

Mushroom compost is excellent for plants as it improves soil structure, water retention, and aeration. However, it’s best used as an amendment rather than a standalone soil.

3. What is a Good pH for Mushroom Compost?

Mushroom compost typically has a neutral pH of around 6.6, making it ideal for most plants.

4. How Do You Mix Mushroom Compost and Soil?

A good starting ratio is 25% mushroom compost to 75% soil. This blend helps improve soil texture and water retention without overwhelming your plants with nutrients.

5. What is the Difference Between Manure and Mushroom Compost?

Manure is animal waste that is rich in nutrients and used as fertilizer. Mushroom compost, on the other hand, is the spent substrate from mushroom farming and is primarily used to improve soil structure rather than for its nutrient content.

6. How to Make Mushroom Compost at Home?

Mix straw, manure, and nitrogen-rich materials like coffee grounds to make mushroom compost. Hot compost the mixture for two weeks and then allow it to cure for another two weeks. Pasteurize or sterilize it if you plan to grow mushrooms.

7. Mushroom Compost for Vegetable Garden – Good or Bad?

Mushroom compost is generally good for vegetable gardens as it improves soil structure and water retention. However, it should be used in moderation, as too much can cause the soil to become waterlogged. Mixing 25% mushroom compost to 75% soil is ideal for most vegetable beds.

This complete guide should provide everything you need to know about using mushroom compost in your garden, from its benefits to how to make it at home. Whether you’re an experienced gardener or a beginner, mushroom compost can be a game-changer for your soil and plants.