Mushroom Compost: What It Is, Its Benefits, and How to Use It

When you hear the phrase “mushroom compost,” you probably think it is compost made out of mushrooms. It’s actually a lot more complicated than that.

Mushroom compost is fungi-infused organic compost that benefits plant growth in your flower bed or vegetable garden. The compost breaks down clay-like soil that would otherwise be hard to plant in. It’s a valuable addition to your garden for building up the nutrients in the soil but should be used sparingly as a soil conditioner.

For gardeners who prefer to garden using organic material, composting is an excellent alternative to synthetic fertilizers. Mushroom compost introduces nutrients and makes the soil’s texture more hospitable to plants and moisture.

What is Mushroom Compost?

Mushroom compost, also known as mushroom soil, comes in two stages: mushroom substrate and spent mushroom substrate. Both are used differently in the growing process. 

Mushroom substrate is made with wheat straw, manure, and some other ingredients. Composters submerge the straw in water, then combine it with chicken manure. Cow manure or horse manure work, too. Mushroom substrate isn’t picky, as long as you get some sort of manure in there. 

The mixture is then composted hot and moist for several weeks. Next, the mixture is pasteurized to prevent mold from growing in the damp. After that, composters introduce mushroom spores into the compost. Growers then use the mushroom substrate for mushroom production in large quantities. 

Once the mushroom substrate has done its job growing mushroom, it becomes a spent mushroom substrate. Therefore, the mushroom compost you will find for sale at your garden center is probably spent compost, which has already been used to grow mushrooms in.

Spent mushroom compost is still useful in your garden. Most of its nutrients are already consumed, but its main job in your garden is to break up dense clay and improve your soil’s quality.

Is Mushroom Compost Better than Regular Compost?

Mushroom compost is an organic matter that can greatly benefit the soil in your vegetable garden. But before you go outside and plant seeds directly into your mushroom compost, know that it is not a suitable replacement for the soil already in your garden, but better as a soil amendment. 

A research project at Pennsylvania State University concluded that fresh mushroom compost: “improves soil structure, provides plant nutrients, increases plant nutrient availability, increases soil microbial populations, increases soil cation exchange capacity, increases plant root structure, increases soil aeration, improves soil water status, and reduces soil compaction.”

Mushroom compost retains water really well and can keep your soil moist for longer. While this is good for breaking down and improving more dense, clay-heavy soils, be careful when using organic mushroom compost. Its ability to retain water can actually cause your soil to retain too much water. This can be hard on some of your plants, especially seedlings and young plants.

How To Use Mushroom Compost

Mushroom compost, as its name would suggest, is mainly used for growing edible mushroom plants. This is because the mycelium flourishes in the hot, damp organic material. However, unless you are a mushroom grower, you will use mushroom compost to supplement your garden’s native soil.

When you use mushroom compost as mulch, it makes it harder for weeds to take root and grow. If your garden’s native soil is dense and clay-like, mushroom compost can soften and break it up a bit. Distributed lightly over your lawn or flower bed, it can improve the quality of the plants and prevent too many weeds from growing.

If you buy spent mushroom substrate, keep in mind that it has been sterilized before bagging. If you want to activate beneficial microorganisms in the mushroom compost, mix it with regular compost. Use it sparingly, 50 percent mushroom compost at most. If your garden is in raised beds, use up to 25 percent mushroom compost.

What is Mushroom Compost Best Used For

Mushroom compost is an excellent fertilizer for your vegetable garden. Cabbage, broccoli, cauliflower, and kale all grow well with a little help from fresh mushroom compost. 

It also mixes well with a tomato plant. Tomatoes benefit from water retained in the soil by mushroom compost, and the alkaline matter in the compost also protects the tomato plant from certain kinds of rot. Tomato growers should use mushroom compost to supplement their garden.

What is Mushroom Compost Not Good For?

Do not use mushroom compost to replace soil. Mushroom compost is more of a soil conditioner, and you shouldn’t use too much of it. 

Plants that don’t thrive in salty conditions will not grow well in mushroom compost. Blueberries, for example, are salt sensitive plants and won’t grow well in mushroom compost.

Seeds, seedlings, and young plants may be negatively affected by too much mushroom compost in the soil.

Mushroom Compost Alternatives

When fertilizing your garden soil, you can use cow manure as an alternative to mushroom compost. Make sure you allow the manure to age and break down in your compost pile before use since it contains ammonia, weed seed, and bacteria that could be harmful to your plants.

Coffee grounds are a popular alternative to mushroom compost since they are easier to acquire. If you are a home mushroom grower, coffee grounds are a solid option, and probably more readily available than cow manure.

Other materials that mushrooms thrive in include peat moss, hardwood dust, and corn cobs, creating air pockets in the compost pile and speeding up decomposition. Whatever material you use, you will have to sterilize it first.

Final Thoughts

Once a batch of mushroom substrate has finished growing mushrooms, its work isn’t over. Like everything organic, its remains have a chance at a second life. Spent mushroom substrate becomes fertilizer for the average vegetable garden like yours.

If your garden soil is dense and clay-heavy, mushroom compost mixed judiciously into the native soil can benefit the health of your garden. Mushroom compost organically aerates the soil and helps it retain moisturization. So say hello to your healthy, happy plants.


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