What to Do About Mushrooms Growing in Your Compost Bin

Sometimes we get asked about the appearance of toadstools in SylvaGrow. If you see fungi in your compost, don’t panic! They’re our friends.

From time to time, depending on climatic conditions, you may see mushrooms in your peat-free compost. For many people, this can be a concern. We are often told mushrooms and fungi are bad. They are linked to rot and poisons, which we don’t want on our plants, especially if we are growing food. But new scientific discoveries have taught us more about the fascinating world of fungi. For example, we now know that most fungi are very good for plants.

Let’s start by dealing with the difference between the terms ‘toadstool’ and ‘mushroom’. “Mushroom” is often used to describe fungi that can be eaten, while “toadstool” is a more general word for fungi that have a stem and a cap. In fact, there is no scientific difference between them, and the terms can be used interchangeably.

Mushrooms are the fruits of certain types of fungi. Just like apple trees bear apples, fungi bear mushrooms. Most fungus is under the soil and invisible to the naked eye. So, the chances are that there are still fungi even if you don’t see mushrooms.

As an avid composter, few things are more satisfying than lifting the lid on your compost bin and seeing rich, dark crumbly compost. But sometimes, you may also find delicate mushrooms poking up through the compost

Mushrooms growing in compost bins are very common. After all, compost bins provide ideal conditions for fungi growth – moisture, shade, and plenty of organic matter to feed on.

If you’ve spotted mushrooms in your compost, you may be wondering why they are there and if they are harmful Read on to learn everything you need to know about mushrooms in compost and what to do about them

Why Mushrooms Grow in Compost Bins

Mushrooms are fungi that thrive in the same warm, moist, shady conditions that are ideal for composting. A compost pile contains a diverse community of microorganisms that aid decomposition. Fungi play a vital role in breaking down tough, woody plant matter in compost.

As organic materials like leaves grass and vegetable scraps decompose, fungi release enzymes that help break down lignin and cellulose. These are complex compounds found in plant cell walls that are difficult for other composting organisms to digest.

Fungi also grow thread-like mycelium networks that spread through the compost, helping distribute moisture and nutrients. When conditions are right, like after a heavy rain, the mycelium may fruit as mushrooms.

Spores land in compost through the air or when new materials are added. The spores germinate if moisture levels and temperatures are suitable. Warmer piles around 90°F (32°C) tend to suppress mushroom growth.

Signs of Healthy Compost

Mushrooms usually indicate that your compost pile has a good balance of materials, moisture, and aeration. Their presence means fungal decomposers are hard at work breaking down organic matter.

So while surprising, mushrooms often signify a healthy composting process. They are nature’s way of reclaiming nutrients and returning them to the soil.

Potential Risks of Mushrooms in Compost

Mushrooms are not necessarily harmful in compost. However, there are some risks to be aware of:

  • Toxic mushrooms – While most are harmless, some mushrooms can be poisonous. Take care to identify any mushrooms growing in open piles accessible to children or pets. Remove unidentified mushrooms as a precaution.

  • Diseases or pests – Dense clusters of mushrooms can attract pests like fungus gnats. They may also harbor plant or human pathogens in rare cases. Monitor your pile closely.

  • Nutrient imbalance – An overabundance of fungi can signal too many woody materials and not enough nitrogen-rich greens. Make sure to add a proper balance of materials.

  • Slowed decomposition – Too many mushrooms may indicate your compost is too wet, compacted, or lacking oxygen. This slows down decomposition. Turn and fluff the pile to increase airflow.

So while mushrooms aren’t necessarily problematic in compost, keeping an eye on your pile is still wise. Address any underlying issues that may be contributing to excessive fungal growth.

Tips to Control Mushrooms in Compost

If you wish to curtail mushroom growth in your compost bin, try these troubleshooting tips:

  • Turn the compost pile frequently to disturb fungal networks and increase airflow. Fungi thrive in undisturbed piles.

  • Add more “green” nitrogen-rich materials like grass clippings, fruit and vegetable scraps, or coffee grounds. This gives bacteria a competitive edge over fungi.

  • Introduce red wiggler worms to break up mycelium as they move through compost. Their tunneling improves aeration.

  • Avoid over-watering and let the pile dry out between waterings. Lower moisture discourages fungi.

  • Chop materials like leaves and straw finely to speed decomposition. Fungi flourish on coarse, slowly decaying particles.

  • Cover fresh food scraps with a layer of leaves or sawdust to conceal them from fungal growth.

  • Apply a thin layer of garden lime on the pile surface to raise pH. Most fungi prefer neutral or acidic conditions.

  • Turn the pile and check its internal temperature. Hot composting above 130°F (54°C) will destroy mushrooms and their spores.

Using Mushroom Compost in Your Garden

Mushroom compost refers to a soil amendment created from the leftover substrate used to grow mushrooms commercially. This nutritious material contains mycelium and other organic matter.

When added to garden beds or potting mixes, mushroom compost introduces beneficial microbes and fungi into the soil ecosystem. The mycelium helps retain soil moisture and make nutrients accessible to plant roots.

However, mushroom compost also carries a risk of growing mushrooms. To reduce this risk, apply compost in a thin layer mixed into the top few inches of soil, keeping it below the surface.

Growing Edible Mushrooms in Compost

For the adventurous gardener, letting mushrooms grow in your compost pile provides the chance to cultivate edible varieties right at home. Here are some tasty mushrooms you can try growing in compost:

Oyster mushrooms – These have a mild, anise-tinged flavor. Introduce oyster mushroom spawn into straw piles and keep them lightly moistened.

Wine cap mushrooms – Also called King Stropharia, these nutty mushrooms thrive on woody mulch and compost. They are easy to grow in gardens.

Almond mushrooms – Known for their slightly sweet, nutty taste. They grow well buried in compost beds under mulch.

Blewits – These blue-tinged mushrooms enjoy partly decayed leaves and grow well in composted soil. They have an earthy, woodsy flavor.

When growing edible mushrooms, always confirm the identification before consuming any mushrooms. While most compost mushrooms are non-toxic, some inedible species can sprout that look similar to edibles.

Troubleshooting Excessive Mushroom Growth

While some mushrooms in compost are normal, prolific growth may indicate underlying problems. Here are some common causes and solutions:

Problem: Mushrooms are taking over the entire surface of the compost.

Cause: Too much moisture and not enough airflow.

Solution: Turn the pile to dry it out and improve aeration. Add bulking agents like wood chips to create air pockets.

Problem: Mushrooms keep reappearing after removing them.

Cause: Mycelium network is established in the pile.

Solution: Turn the compost frequently to disrupt fungal growth. Maintain temperatures around 130°F (54°C) to destroy mycelium.

Problem: Mushrooms have a foul odor.

Cause: Anaerobic conditions and insufficient nitrogen.

Solution: Add nitrogen-rich greens and turn the pile to introduce oxygen. Check moisture levels.

Problem: Mushrooms growing on just one section of the pile.

Cause: New materials were added, introducing spores.

Solution: Mix new materials thoroughly into the center of the pile right away before fungi takes hold.

Problem: Mushrooms with caps that turn black or melt into black liquid.

Cause: Harmless ink cap mushrooms.

Solution: Ink caps are not hazardous, just unsightly. Simply remove the mushrooms.

When to Worry About Mushrooms in Compost

Consult an expert if you notice any of these warning signs that indicate potentially toxic fungi:

  • Mushrooms with white gills that bruise blue. This may signal Destroying Angels, a deadly mushroom species.

  • Bright red mushrooms with white spots. Could be the toxic fly agaric mushroom.

  • Mushrooms growing near buried pet waste. May be poisonous Chlorophyllum molybdites.

  • Any mushrooms growing on treated lumber, painted wood, or pressure treated materials added to the compost. These are more likely to be toxic.

  • Mushrooms that appear in compost piles after flooding or heavy rain followed by high heat. Dangerous amatoxins can thrive in these conditions.

When in doubt, do not handle mushrooms bare-handed. Use a disposable glove and place the mushroom in an outdoor refuse pile until a mycologist can identify it. Always supervise children and pets around open compost piles.

The Takeaway

Spotting mushrooms growing in your compost bin can be startling but is often completely normal. Fungi naturally thrive in the moist, organic environment inside compost piles. Allowing edible mushrooms to grow can be rewarding for seasoned composters.

For others, controlling mushroom growth may be preferred. Avoid over-watering, turn piles frequently, and maintain a good balance of materials to keep fungi in check. Monitor for rotten odors, pests, or toxic mushroom indicators.

With proper maintenance and precautions, the presence of mushrooms in compost is no cause for alarm. These fascinating decomposers are simply helping speed along the miraculous process of transforming kitchen scraps and yard waste into nutrient-rich garden compost.

Fungi are beneficial to plants

Many people believe that fungi feed on their plants. The honey fungus is one of the few species that will do this, but most plants and fungi live together in harmony. The plant gives the fungi some of its sugars on purpose, and in return, the fungi can make the plant’s roots grow much longer. This helps our plants to source nutrients and water in the soil. The fungi can also help the plant fight off diseases and pests by making a barrier around the roots. This is of huge benefit to the plants.

Are the mushrooms poisonous?

We don’t recommend eating any mushrooms unless you are 100% sure that they are edible. But most mushrooms in the UK are harmless unless eaten in large quantities. If there are mushrooms in the ground, they probably won’t hurt you or the plant, even if they touch it. We recommend rinsing any produce before consumption, but this is good practice whether there are mushrooms or not.

Will adding Mushrooms to Compost Make it Fungal Dominated & More Gardening Q&A


Are mushrooms growing in compost good?

Mushrooms in compost signify a natural and ongoing decomposition process. Understanding their role helps in optimizing compost health and utilizing it effectively in gardens. Remember, while they play a crucial role in nature’s cycle, always exercise caution if tempted to consume them.

Is it safe to compost poisonous mushrooms?

Mushrooms and other fungus grow in your compost pile naturally. It is fine if poisonous mushrooms grow in your compost pile. You will not be eating the compost. The mushroom will break down in the compost and in the soil and pose no danger.

Is mushroom compost OK?

Mushroom compost is excellent on the vegetable garden, as vegetable crops usually grow best when th soil is not acid and where the soil is alkaline brassicas (cabbage, broccoli, cauliflower, kohlrabi, Brussels sprouts and kale) are less likely to be infected by clubroot disease.

Are fungi good for compost?

You do not need to worry about it as it is helping to decompose your compost. These Mycelium fungi are desirable because they bind together single particles of sandy soil into a small crumb creating a larger surface area in proportion to its size.

How to compost mushrooms?

When composting mushrooms, it is essential to choose the right materials. Use a mixture of brown materials like straw, hay, newspaper, and cardboard, and green materials like grass clippings, vegetable scraps, and other organic materials. The ideal ratio is 2:1 brown to green materials. 2. Avoid Cooked Mushrooms

Why do mushrooms grow in my compost?

Fungi can speed up the decomposition process of organic materials. Mushrooms have a high concentration of phosphorus, potassium, and copper, and they also include mycelium, which can degrade tough organic matter and enrich the soil. Are Mushrooms in My Compost Good or Bad? Why Are Mushrooms Growing in My Compost?

Are mushrooms good for composting?

The use of mushroom compost is highly beneficial. It makes your soil richer, and it’s a perfect nutrient supplier. Plus, it improves the absorption of water in the soil. And the most important benefit, mushrooms are the ultimate composter, breaking down organic material and thus accelerating the decomposition process.

Can mushrooms grow in a compost pile?

Mushrooms can actually grow in your compost pile if the conditions are right. While this may seem like a good thing, it can actually be a sign that your compost pile is too wet and not getting enough air.

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