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How Do I Get Rid of Mulch Fungus?

By Christina Edwards
Updated May 16, 2024
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Once it has started, mulch fungus can be difficult to get rid of, and it should be treated as soon as the problem arises. Many gardening experts agree that the best way to deal with mulch fungus is to prevent it from happening in the first place. If your mulch does develop fungus, you can remove the affected portion and replace it with a new layer of mulch. Other methods for treating mulch fungus include heat treatments, pH-changing agents, or fungicide treatments.

Some people simply add a new layer of mulch over the old layers to get rid of mulch fungus. This method often fails, though. Doing this will usually just result in the fungus popping up into the new layers.

If there is any type of mold or fungus growing in your mulch, before adding a new layer many experts advise that you do a few things first. The first thing that you should do whenever you notice that you have a mulch fungus is to remove it. This will help prevent spores from spreading and prevent new crops of fungal growth.

After all of the fungus and surrounding mulch has been removed, you can rake away the top layer of mulch. Discarding both the mold and the top most layer of the mulch will help in preventing new growths of mulch fungus. In particularly bad cases though, all of the mulch may need to be removed.

After the mulch has been removed, turn the soil underneath. You can then add a new layer of mulch. It is important to remember not to have too much mulch, as thick layers can actually encourage certain types of mulch fungus and mold to grow. Many experts believe that one to two inches of mulch is ideal.

One way to kill mulch fungus is to heat it to a temperature of roughly 104 degrees F (40 degrees C). This can be accomplished naturally. To use this method, all or at least most of the mulch must be removed and piled in sunny area. Wet the mulch thoroughly and wait at last a couple of weeks. This will cause the decomposition process to start, which will cause the mulch pile to heat up to temperatures high enough to kill most mold and fungus colonies.

Raising the pH of the mulch and soil can stop many fungal growths completely. Because many fungal growths prefer slightly acidic soil, "sweetening" the soil, or making it less acidic, can work. This can be achieved by adding liquid lime, which can be purchased in the gardening section of many larger chain stores. Sprinkle or spray a small amount of this mixture directly onto the mulch. Be careful not to get it on any plants and not to use too much, as it could possibly be damaging.

Fungicides are also a solution to mulch fungus. Many all-purpose fungicides for gardens are on the market today. Be very careful if you use this method, and follow all directions on the package precisely.

Safer, more organic fungicides may be a better option, considering they are safer for humans and animals and have less of an impact on the environment. Two organic alternatives are cornmeal and regular baking soda. Just about any type of cornmeal will do. To use it, simple sprinkle it over the mulch and water, or soak one cup in one gallon of water and spray or pour onto the mulch. Baking soda can be used in much the same way, only using two tablespoons of it in one gallon of water.

Typically, preventing garden fungus on organic mulch is easier than getting rid of it. Generally, hardwood mulch is more prone to certain types of fungi, and should be avoided. Softwood mulches, such as those made out of pine are often considered better, along with pine needles and other organic materials. Other tips to avoid mulch fungus include turning it frequently and not allowing it to become too wet or dry. Both wet mulch and dry mulch can promote fungal growths.

Is Mulch Fungus Harmful to Humans?

Mulch can be the perfect environment for fungi to reproduce and grow. Luckily, most varieties of mulch fungus are not harmful to humans on their own. Though you should not be alarmed by the presence of fungus, there are some risks you should be aware of before removing it.

Something in the Air

In rare cases, the spores of mulch fungus can be toxic to humans if they are inhaled. Individuals with severe allergies, asthma or compromised immune systems can become ill if they breathe in spores. If you feel you may be at risk, wear a face mask or neck gaiter when landscaping to prevent the inhalation of spores and other allergens.

Not on the Menu

Some types of mulch fungus, like mushrooms, could look appetizing to a clueless dog or curious child. Wild mushrooms can be poisonous and should never be consumed. Put on a pair of gardening gloves and remove any in the yard before letting pets or children play outside. This can be time-consuming and may need to be performed daily. Fortunately, there are antifungal treatments available to keep persistent fungus from growing back.

Does Vinegar Kill Fungus in Mulch?

A diluted vinegar spray can be an effective treatment for mulch fungus. Knowing which type of vinegar to use and how to use it might be beneficial when pesky fungi have taken root in your mulch.

Getting Acidic

Vinegar contains acetic acid, a chemical compound that can eliminate spores and damage fungus. Common types of household products, such as white vinegar and apple cider vinegar, have around 5% acidity and are safe to use around humans and animals. These cost-effective solutions can be found at virtually any grocery store.

Avoid using vinegar with a high percentage of acidity, such as horticultural grade, as this has the potential to kill grass and plants and cause serious harm to animals and humans.

Saying Goodbye, Fungi

If you want to stop the growth of mulch fungus, dilute one part vinegar with four parts water to create a homemade antifungal spray. The spray will work best when used consistently, as it will take some time for the acetic acid to break down any mature fungal growths. Spritz the affected areas of mulch and avoid soaking the soil beneath the mulch with the mixture. Acetic acid can also damage certain plants, so do not spray leaves directly and avoid spraying if it is windy or raining.

What Does Mulch Fungus Look Like?

Mulch fungus is usually benign, but that does not mean it is not unsightly. Some fungi are easily identified, and others seem like they are from another planet. Here are some common types of mulch fungus and what they look like:

  • Mushrooms: Also known as toadstools, these familiar fungi come in all shapes and sizes. Most mushrooms are easy to spot from their signature caps, which can be flat or rounded. They come in a range of colors, but common ones include white, pale yellow, or brown.
  • Artillery fungus: These are tiny cup-shaped fungi with a sticky black spot in the middle. This black spot is a spore mass, which is ejected from the fungus and carried by the wind to reproduce. The spore mass sticks to the sides of houses or on the leaves of plants and looks like a speck of tar.
  • Slime molds: Aptly nicknamed "dog vomit" fungus, slime molds appear as lumpy masses in mulch. They are typically yellow or orange and later turn brown as they dry out. In the final stages, slime molds become white and powdery.
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Discussion Comments
By SoilFoodWeb — On Dec 14, 2019

Wow-this is completely off-base. Healthy soil is replete with beneficial fungi that help provide plant available nutrients from the surrounding organic matter and inorganic minerals. Fungi are also critical for soil to build soil structure so water and oxygen can diffuse into your soil. The fastest way to make your soil worse is to kill all the fungi which causes soil structure to collapse leading to low oxygen conditions. The microbiology that lives in low oxygen conditions actually off-gas the nutrients and produce many plant toxic compounds. While there are many fungal plant pathogens, encouraging the beneficial fungi in your soil will inhibit the pathogens. Read up and educate yourself on the soil food web (google it) and how the beneficial organisms in the soil, of which fungi are critical, actually help your plants. An organic mulch layer is a great way to keep the fungi happy, removing them is taking a step backwards--maybe two or three especially if you then "turn your soil" after removing them, since this effectively destroys whatever structure the fungi have so diligently built up. I would like to know who the "many experts" are that recommend this strategy. They are certainly not soil ecologists.

By Terrificli — On Apr 26, 2014

@Vincenzo -- using that method will actually help create an environment in which fungus likes to grow. Think about it -- the problem with black plastic bags is that they make it difficult for moisture to escape the garden bed. Fungus just loves moisture and will be more likely to crop up in that scenario. For weed prevention, you're better off with a "weed mat." Those do help ward off weeds and have holes in them so that water can escape into the soil and fungus is less likely to attack plants at the roots.

By Vincenzo — On Apr 25, 2014

Around these parts, a lot of people start off their gardens by lining the garden bed with plastic (often black plastic garbage bags), covering those with dirt and then adding mulch after the plants are in place. The goal of doing that is to prevent weeds.

Will using that technique also prevent mulch fungus?

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