What to Do About Mushrooms Growing in Your Compost Bin

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.