What is mushroom compost made of?
Mushroom compost is a good way to provide extra nutrients to plants, and an even better way to improve the condition of your soil. But what is mushroom compost? It’s a byproduct of mushroom farming, so is often available in large quantities and quite cheaply. Mushroom compost can differ greatly from batch to batch, depending on the source, so let’s explore what’s in it and how to use it.
Is mushroom compost good for all plants?
Mushroom compost can contain a very varied mixture of ingredients. Each farmer will have a preferred blend, and will typically include any of the following:
- Chalk
- Dried blood
- Gypsum
- Hay
- Lime
- Manure
- Moss
- Peat
- Straw
- Vegetable waste
Of these ingredients, peat is an unsustainable compost ingredient which is used less and less commercially, as it is now known to contribute to the destruction of environmentally important peatlands. Manure and dried blood are of course sourced from animals, so may not suit those who want to grow following vegan principles.
As some mushroom compost mixes will contain lime and chalk, be careful using it around acid loving plants, such as heathers and camellias. These ericaceous plants need special compost such as leaf mould and will not appreciate the acidity being reduced.
Also be weary of any inorganic pesticides and fungicides which may have been used when producing mushrooms. Traces of these can remain in the spent compost and can damage plants.
Be alert to these ingredients, but don’t let them put you off using mushroom compost. Like many other types of compost, it is a great way to improve the moisture retaining capabilities and aeration of your soil. It’s also one of the best ways to achieve a more workable soil, especially hard, clumpy clay, and dusty, sandy soil. Add to the surface in the winter and leave for soil microorganisms to break it down and work into the soil for you.
Can you grow vegetables in mushroom compost?
Mushroom compost is excellent for growing veggies. Asparagus, tomatoes, potatoes, aubergines, carrots, spring onions - you name the vegetable, it will grow in mushroom compost. And there are some vegetables which will especially enjoy mushroom compost - those which prefer alkaline soil. Think about using when growing brassicas, such as broccoli, Brussels sprouts, cabbage, cauliflower, kale, kohlrabi, radish and rocket.
Fruit bushes for example are plants that don’t like mushroom compost, so use wood chip to mulch these instead.
Mushroom compost can be applied straight to soil as a mulch around established plants. Don’t allow it to touch the leaves or stem, as the soluble salts in the compost can damage the plant. Mushroom compost can be used in containers, but should be mixed with a general purpose compost at a rate of about 50/50.
Don’t use fresh mushroom compost in potting mix for seedlings, or for potting up young plants, until it has matured. Leaving it for six months or more will allow the salts to disperse.
How to make mushroom compost at home
Try to purchase mushroom compost from garden centres and nurseries, unless you are lucky enough to live near a mushroom farm! If that is the case, you may be able to obtain large quantities of mushroom compost and even negotiate having it delivered straight to you. Commercially produced mushroom compost will have been steamed to destroy any viable weed seeds.
To make a comparable mushroom compost formula yourself, you will need to have the means to maintain a pile of compost at a temperature of 71°C (160°F) for a few days. Turn it every 48 hours to introduce air and to ensure that all parts of the pile achieve the same temperatures. Add water if it looks like the pile is drying out. After two weeks, move the processed compost to a new pile, and allow to sit for a further two weeks before using.
Frequently asked questions about mushroom compost
Can mushroom compost burn plants?
Yes, fresh mushroom compost can be too strong for young plants and seedlings, depending on the ingredients used to make it. Use around established plants or allow it to mature before using on younger plants when it should be mixed with a general purpose compost.
Where should you not use mushroom compost?
Avoid using mushroom compost on acid-loving plants, such as blueberries and heathers.
Do worms like mushroom compost?
Yes, worms like mushroom compost, and will help to mix it in with other material in the soil.
Will mushroom compost cause honey fungus?
No, mushroom compost and honey fungus are completely unrelated. You may see mushrooms popping up from the mushroom compost, but these are nothing to worry about.
