How to Get Rid of Mulch Fungus

Sharing is caring!

For novice gardeners, figuring out how to get rid of mulch fungus is a frequent query. It’s understandably distressing to discover fungus proliferating on your mulch, especially when mulching is meant to improve your gardening efforts.

Mulching brings a wealth of benefits to your garden, from preserving soil moisture and weed control to enhancing plant growth and overall aesthetic appeal.

However, using mulch in your garden might sometimes invite the issue of mulch fungus. Fortunately, there are several effective methods to address this concern, which we will delve into in this article.

What Causes Mulch Fungus?

There are various reasons you get fungus in your mulch, but the most important factor is the mulch itself. Given the right conditions, it is the perfect environment for fungi to thrive.

Fungal spores, which are the reproductive units of fungi that eventually develop into fungi, may contaminate your mulch by various means.

Spores may enter your garden via wind dispersal, unhealthy gardening practices, or they may already be present in the mulch when you acquire it. These spores can remain dormant until the right conditions cause them to grow.

Fungi help with decomposition and feed on rotting organic matter, which mulch is already rich in. Additional favorable conditions such as high moisture content, warmth, and lack of exposure to sunlight, help these fungi grow.

How to Get Rid of Mulch Fungus

Here are the best ways to get rid of mulch fungus:

1. Remove contaminated mulch

Mulch
Big piles of Mulch.

Materials needed:

  • Rubber gloves
  • Protective clothing – anything that covers your arms and legs is fine
  • Mask or respirator – to prevent you from inhaling spores
  • Plastic bag – to collect contaminated mulch

If you spot mulch fungi early enough, you can control the infestation by removing affected mulch by hand. This method is most effective when you’re working with mushroom fungi and other fruiting types where the extent of infestation is easy to see.

Steps:

  • Remove contaminated mulch by hand
  • Remove mulch under and around the contaminated site
  • Place the mulch you remove in a plastic bag to discard later

It’s best not to limit removal to mulch that is obviously contaminated.

Surrounding mulch may contain spores and fungi still in their early stages of development. Not removing these potentially contaminated mulch increases the chance of seeing new fungal growth soon.

You should wear gloves and facemasks when removing mulch fungus by hand, especially if you don’t know what type you’re dealing with. This reduces the chance of reacting to spores and mycotoxins to which you may be allergic.

Using a plastic bag to hold contaminated mulch prevents wind from dispersing fungal spores from the mulch you’ve just removed.

2. Reduce mulch acidity

Mulch in a bag.
Mulch in a bag.

Materials needed:

  • Lime, wood ash, or baking soda
  • Bucket or bowl – if using baking soda
  • Water

Reducing your mulch acidity means raising its pH or making it more alkaline. You can do this using lime, wood ash, or baking soda.

The reason this method works is that the types of fungi you find on mulch grow best in moist, acidic environments.

When you reduce the acidity of your mulch, the mulch becomes inhospitable for fungi living on it. This is often enough to kill resident fungi and inhibit future fungal growth for a while.

How to use lime or wood ash

  • Spray your wood ash or lime over the mulch fungus

If you choose to use lime to raise your mulch pH, liquid lime works well because it’s fast-acting. You can also use lime pellets, which act more slowly but can reduce the risk of overliming your mulch.

You can make wood ash yourself by burning wood or opt for baking soda if you find it more accessible. 

How to use baking soda

  • Mix 2 teaspoons of baking soda with 1 gallon of water in a bowl or bucket
  • Pour the mixture over the contaminated mulch and leave it

How much baking soda to use depends on the extent of your infestation, but the fungus will die as the environment slowly turns alkaline. This could take anywhere from a few hours to a few days.

One major caveat to raising your mulch pH is that you might hurt your plants while saving your mulch.

Some plants grow best in acidic soil. If raising your mulch pH also raises your soil pH, the now-more-alkaline environment might impair plant development.

To avoid this, be mindful of how much lime, wood ash, or baking soda you use.

Make sure the plants around the mulch you’re treating can tolerate pH changes. You should also avoid applying lime, wood ash, or baking soda close to plant roots.

3. Treat with vinegar

White vinegar in a glass bottle on a wooden counter.
White vinegar in a glass bottle on a wooden counter.

Materials needed:

  • Vinegar
  • Water
  • Spray bottle

Vinegar works differently from lime or wood ash because it raises mulch acidity instead of lowering it. While fungi like acidic environments, the acetic acid in vinegar is toxic to fungi and their spores.

You can make vinegar sprays using apple cider vinegar, white vinegar, or other types of vinegar with low acid content. This is so you don’t over-acidify your mulch and surrounding soil, which can hurt plants that don’t like highly acidic environments.

Steps:

  • Create your vinegar spray by mixing water and vinegar in a 4:1 ratio
  • Spray this mix over mulch fungus while avoiding contact with plant parts

Avoid spraying vinegar in rainy conditions as rain will simply wash it off the mulch.

Although vinegar lowers pH, the increased acidity is short-lived because vinegar breaks down quickly. You might need to repeat this process a few times to kill all the fungi on your mulch.

4. Apply cornmeal

Cornmeal close-up.
Cornmeal close-up.

Materials needed:

  • Cornmeal
  • Water
  • Bucket or bowl

Cornmeal has natural antifungal properties, which many gardeners say help in controlling mulch fungus. Applying cornmeal over an infested area can help you kill mulch fungus and prevent spores from maturing.

Steps:

  • Mix one cup of cornmeal with a gallon of water
  • Let the mixture sit for a while
  • Pour it over fungal colonies in your garden

5. Spray with bleach

Bleach applied on a tree with a brush.
Bleach applied on a tree with a brush.

Materials needed:

  • Bleach
  • Rubber gloves
  • Spray bottle

Think of bleach as your makeshift fungicide. It is often used in disinfecting plant stems and growth media, so it can be used as a fungicide if necessary.

Steps:

  • Mix bleach and water in a 1:9 ratio
  • Spray this diluted mixture over contaminated mulch

If your bleach isn’t well diluted ensure it doesn’t touch plant parts since it might damage them.

6. Fungicides

Fungicides
Fungicides

Materials needed:

  • Fungicide
  • Protective clothing
  • Mask or respirator
  • Rubber gloves
  • Spray bottle

Chemical fungicides are often a last resort for eliminating mulch fungus, but they work well. They are cheap and fast-acting, but the chemicals may also contaminate your soil. This could harm your plants and kill beneficial soil microbes.

Organic fungicides and fungicides with biodegradable components are more eco-friendly alternatives to synthetic chemicals, but they aren’t always as fast-acting.

Steps:

  • Wear clothing that protects your nose, skin, and eyes regardless of the type of fungicide you choose to use
  • Pour fungicide into a spray bottle and over the mulch fungus and surrounding area

Don’t use more fungicide than necessary and avoid spraying fungicides on plant parts. Even if organic, fungicides can harm plants.

7. Heat the mulch

Heat mulch
Heat mulch

Materials needed:

  • Spade or shovel
  • Rubber gloves
  • Water

This method involves the removal of mulch with fungi. But instead of discarding the contaminated mulch as you normally would, you raise the temperature.

High temperatures between 110 to 140 ℉ are effective at killing mulch fungi. And don’t worry, you don’t need to light a fire. You can do this naturally, but it can take up a few weeks.

Steps:

  • Remove the contaminated mulch
  • Gather it in a heap in a sunny place
  • Wet it completely with water
  • Let the soaked heap dry

This method accelerates decomposition, raising the temperature of the mulch to levels needed to kill fungi living in it.

How to Prevent Mulch Fungus

You can’t completely prevent mulch fungus, but there are steps you can take to reduce the likelihood of an infestation. These methods rely on creating an environment unsuitable for fungi development.

Here are some of them:

1. Don’t overwater

Fungi thrive in wet environments. To prevent fungi from festering, don’t let your mulch stay wet for long periods.

There’s not much you can do about rain, but you can be more strategic in how you water your plants.

Only water plants when necessary and ensure you don’t wet large portions of mulch if there are no plants growing there. You should also leave gaps between watering periods for your mulch to dry.

2. Rake often

Raking helps expose bottom layers of mulch. These layers of mulch are often high in moisture and may be buried too deep to be dried by regular sunlight exposure, especially during wet seasons.

Exposing these mulch layers via raking allows them to get sun or air-dried, reducing the chances that fungi spores within them will fester. 

3. Limit composts and organic fertilizers

Composts and organic fertilizers can be good, but they are potential sources of fungus. This is particularly true of composts high in woody material.

The main reason experts sometimes advise against using them in your garden is that it’s not always clear just what they contain. They may contain fungi spores, bacteria, or other pathogens and parasites which may infest your garden and harm your plants.

If you intend to use organic fertilizers, ensure you get them from certified dealers. You can also sterilize the compost you plan to use in your garden.

4. Sterilize gardening equipment

The tools you use in your garden may be sources of fungi. These tools might get contaminated with fungi where you store them or from use on others’ gardens.

If your tools have fungi spores, using them in your garden can introduce fungi to your mulch.

Regularly clean gardening equipment using disinfectants like bleach to kill whatever fungi may be resident on them.

5. Choose the right type of mulch

Some types of mulch are more susceptible to fungus than others. For example, hardwood mulch is more susceptible to fungal colonization than softwood mulch. Mulch made from decaying fallen trees are also more likely to support nuisance fungi.

Mulch made from softwood, twigs, and small branches reduce the likelihood of fungal growth. Ensure you don’t overuse them though. One to two inches of mulch is fine; more might retain too much moisture and support fungal growth.

Common Types of Mulch Fungi

There are several types of mulch fungi, but these are the ones you’re most likely to encounter in your garden:

1. Artillery fungus

Artilllery fungus close-up.
Artilllery fungus close-up.

This is a hardy fungus that’s attracted to light and bright surfaces. Artillery fungal masses usually have cream or orange cup-shaped fruiting structures containing black spores.

When the fungus has absorbed enough moisture from mulch, the cups shoot out the spores within them. These spores can travel long distances before landing on new surfaces on which they develop into new fungal masses.

The “artillery” in this fungus’ name comes from this dispersal method. This fungus is a major concern for landscapers and gardeners because the spores stick to surfaces like walls and plants and are very hard to remove.

Although you can kill this fungus using the methods described in here, getting rid of the fungal patches is difficult.

2. Stinkhorn fungus

Stickhorn fungus close-up.
Stickhorn fungus close-up.

You’ll usually find stinkhorn fungus on decomposing mulch made of hardwood. As its name suggests, this fungus has an odorous smell.

There are different species of stinkhorn fungus with different sizes and foulness. However, they all resemble slimy gelatinous cylindrical masses with white or cream bodies that ease into orange or brown near the top.

Stinkhorn fungi usually appear during rainy periods, drying out shortly after the weather becomes drier. They aren’t difficult to treat, and they are harmless to plants and humans.

3. Slime mold

Slime mold close-up.
Slime mold close-up.

Although often considered mulch fungi, slime molds aren’t fungi at all. These blob-like masses are actually amoeba.

Some white slime mold species are known colloquially as “dog vomit.” This name stems from the resemblance of the masses to dog vomit.

Slime molds are particularly disconcerting to encounter because of their appearance and ability to spread quickly. Within a day, this single-celled amoeba can spread a few feet from its starting point.

Slime molds can spread from mulch and climb plants in search of food. Although this sight is upsetting, the molds aren’t dangerous to plants or humans.

Slime molds are easy to get rid of. You can wash them off plants and mulch using high-pressure water sprays.

You can also use vinegar, baking soda, or cornmeal to kill them.

4. Bird’s nest fungus

Bird's nest fungus close-up.
Bird’s nest fungus close-up.

This fungus’ name comes from the resemblance of its fruiting body to an egg-filled nest. You’ll usually find it mulch rich in decomposing matter along with artillery fungus, but it is relatively larger.

Bird’s nest fungi often aggregate around the same spot although the buds are never joined together. When rain drops strike the bird’s nests, the nests launch spores trapped inside them a few feet away from the nest.

Bird’s nest fungi are easily eliminated by hand removal or through the use of lime, vinegar, baking soda, and fungicides.

5. Toadstool mushrooms

Toadstool mushroom close-up.
Toadstool mushroom close-up.

Toadstool mushrooms are among the most easily recognized groups of fungi. They have umbrella-like crowns and are often found decomposing hardwood mulch.

Toadstool mulch fungi aren’t harmful to touch, but they can be highly poisonous if ingested.

Frequently Asked Questions

Here are some of the most asked questions about how to get rid of mulch fungus.

Is mulch fungus harmful to humans?

How to Get Rid of Mulch Fungus

Most types of fungi you find on mulch are not toxic to humans. However, some fungi secrete mycotoxins that are poisonous if ingested.

Sometimes, even normally harmless fungi can trigger allergic reactions in sensitive individuals exposed to them.

Is mulch fungus bad for plants?

Stickhorn fungus close-up.

No, mulch fungus usually isn’t bad for plants. In fact, it can be good because it accelerates mulch decomposition. This leads to the release of nutrients into the soil.

However, their often unsightly nature is a bother for many gardeners because large infestations can destroy the landscape.

Can you permanently get rid of mulch fungus?

Artilllery fungus close-up.

No, you can’t permanently stop your mulch from having fungus. However, you can reduce the likelihood of an infestation using some of the strategies in this guide.

How do I get rid of artillery fungus in mulch?

Slime mold close-up.

Artillery fungus can be tough to deal with. Fortunately, you can kill them using strategies discussed here, from liming and pH alteration to fungicide use.

Why am I getting fungus in my mulch?

Toadstool mushroom close-up.

You may be getting fungus in your mulch because you overwater it, don’t rake it often, are using contaminated gardening equipment, or don’t expose it to enough sunlight.

Does vinegar kill mulch fungus?

Bird's nest fungus close-up.

Yes, vinegar kills mulch fungus. However, you may need several rounds of spraying to eliminate all of the fungi in your mulch.

What is the best fungus killer for mulch?

How to Get Rid of Mulch Fungus

In terms of effectiveness, synthetic chemical fungicides are the best mulch fungus killers. However, cornmeal, vinegar, and alkalizing agents like lime and baking soda may be more eco-friendly options.

Conclusion

Most of the concern with how to get rid of mulch fungus stems from discomfort with their appearance or misconceptions about mulch fungi.

Though landscapers and gardeners are quick to rid their mulch of fungi, most of these fungi are harmless to plants. Many are even beneficial.

Still, extensive fungal colonization can destroy fine mulch landscapes. Another reason you might want to eliminate mulch fungi is that potentially poisonous species that are colorful may attract children or pets who might ingest them.

Fortunately, mulch fungus isn’t hard to get rid of. Any of the strategies here can help you fix an infestation.

It’s best to try non-chemical methods first. But if you’re dealing with stubborn infestations, chemical fungicides will work fine.

Ensure you also take actions to prevent infestations so you don’t have to deal with this problem too often.

Know other ways to get rid of mulch fungus? Share with us in the comments.

More on mulch

Leave a Comment