Common Mulch Fungus: Does Mulch Cause Fungus And Can It Be Treated

Common Mulch Fungus: Does Mulch Cause Fungus And Can It Be Treated

Most gardeners take advantage of organic mulch, such as bark chips, leaf mulch or compost, which is attractive in the landscape, healthy for growing plants, and beneficial to the soil. In fact, various fungi are natural components of this rich, organic environment.

Does Mulch Cause Fungus?

Mulch doesn’t directly cause fungus, but when certain conditions are present, mulch and fungus work together in a symbiotic relationship; fungi are living organisms that develop as part of the natural decomposition process.

Many types of fungi help break down woody tissues and other types survive by consuming bacteria in the mulch. Either way, fungus is beneficial so no mulch fungus treatment is necessary in most cases. As the fungi speeds decomposition, the decomposed mulch improves soil fertility by making nutrients more available to other plants. Decomposed mulch also increases the soil’s water retention capabilities.

Types of Fungus in Mulch

Both molds and fungus are a normal part of the decomposition process. Here is some of the most common mulch fungus seen in the landscape:


Mushrooms are a common, familiar type of fungus. You may see mushrooms in a variety of colors and in sizes ranging from tiny puffballs measuring less than an inch (3 cm.) to varieties that attain heights of several inches (8 cm.). Stinkhorns are commonly seen in mulch.

Some people think mushrooms are a nuisance, but they aren’t harmful in most regards. However, while some mushrooms are safe to eat, many are highly toxic – even deadly. If this is a concern, or if you have curious children or pets, rake or mow the mushrooms and dispose of them safely.

Slime Mold

Slime molds, also known as “dog vomit,” tend to be nuisances, but their growth is usually confined to small areas in damp mulch or old, rotting logs. Slime mold is easily recognized by its bright pink, orange or yellow color.

As mulch fungus, treatment of slime mold involves raking the surface of the mulch frequently to prevent growth. You can also remove the slimy substance with a rake, then dispose of it away from your yard. Otherwise, let the mold complete its natural lifespan and it will dry out, turn brown and become a powdery, white mass that is easily blasted with a garden hose.

Bird’s Nest Fungus

Bird’s nest fungi looks exactly like their name suggests -tiny bird nests complete with eggs in the center. Each “nest” measures up to ¼ inch (6 Mm.) in diameter, growing in small clumps usually limited to a few inches (8 cm.). This interesting little fungus is harmless and nontoxic.

Artillery Fungus

Artillery fungus resembles a tiny cup with one black egg in the center. Artillery fungus is named for its sticky spores that burst and can be windblown considerable heights and distances.

Although this fungus grows in mulch, it is also attracted to light-colored surfaces, including cars or houses. The spores, which resemble specks of tar, can be difficult to remove. Other than its annoying, unsightly qualities, it isn’t harmful to plants, pets or people.

There is no known cure for artillery fungus. If this fungus is a problem in your area, avoid using wood mulch adjacent to buildings. If mulch is already in place, rake it often to keep it dry and aerated. Large chunks of bark are less inviting than shredded mulch or small pieces.

What kind of fungus grows in mulch?

Beside above, what is white fungus on mulch? As mulch fungus, treatment of slime mold involves raking the surface of the mulch frequently to prevent growth. Otherwise, let the mold complete its natural lifespan and it will dry out, turn brown and become a powdery, white mass that is easily blasted with a garden hose.

Keeping this in consideration, how do you get rid of fungus in mulch?

One simple way to get rid of mold is to turn it over into the topsoil and wet it down with water. A second way is to loosen it up with a rake to allow air to circulate around it and help to dry it out. A third way is to remove the mulch and place it in a pile and soak the pile with water.

How do you get rid of fungus in flower beds?

Cut off any damaged parts of the flowers and dispose of them, as well. To avoid spreading fungi, disinfect the shears or scissors with a solution of 1 part bleach and 3 parts water. Soak them for five minutes then rinse and air dry after pruning the affected plants.

Why Is My Mulch Moldy?

Many homeowners will use wood chips as a decorative feature in their front or back yards. Gardeners may use wood chips as mulch, but they also have the option of using compost, grass clippings, fallen leaves, pine needles, paper, or cardboard as mulch.

Wood chips are often used as mulch, although you can use many other materials like grass clippings or leaves.

Mulch does have many benefits, such as insulating soil from extreme temperatures and maintaining moisture levels. However, mulch itself is often composed of organic material such as wood, plant fiber, or paper. This organic material provides the perfect food for mold to grow – but conditions must be right.

Organic material alone is not enough to allow mold to grow. Mold will only thrive when there is enough moisture in the mulch or in the air, and when temperatures are warm (77 to 86 degrees Fahrenheit, or 25 to 30 degrees Fahrenheit).

Mold and other fungi, like mushrooms, are more likely to appear when mulch is moist and warm, such as after a summer rain.

This is why you will often see mold begin to appear on mulch in the spring or summer, especially after a few days of rainfall. As temperatures get warmer and mulch stays wet for longer periods of time, mold growth becomes more likely.

Fact Sheets And Publications

Landscape mulch usually consists of hardwood shreds or bark chips, providing cover to hold moisture and add a finished look. Wood in mulch also provides a food source for fungi that are natural decomposers, breaking down plant material and utilizing organic matter. Without fungi, dead leaves, twigs and branches would clutter forests and landscapes. We see fungal fruiting bodies after growth of threadlike mycelium in soil and mulch. The most recognizable of these spore producing bodies are mushrooms, but sometimes they produce other structures, such as:

A common surface mold is slime mold (ex. Physarum sp.) that will rapidly grow over the surface of mulched areas, characterized by a yellow, orange, or white, soft gooey mass. They are harmless, and can be raked away. Undisturbed, they will produce spores and then dry up, but may grow again after rain events.

Stinkhorns (ex. Mutinus sp.) are common, characterized by an upright tube like structure that may reach 6 to 7 inches in height overnight. Stinkhorns have a slimy, smelly cap on which spores are produced. The smell attracts insects to the cap where they pick up spores and carry them to new locations. Stinkhorns are harmless and may be broken up by raking lightly over mulch.

Bird’s nest fungi (ex. Cyathus sp.) produce small (1/4 inch or smaller) cup-shaped fruiting bodies on top of mulch, usually in clusters. Cups have very small round spore bodies (peridioles) in the bottom, which look like miniature eggs in a bird nest. Spore bodies (eggs) are splashed out of cups during rains, or moved around by animals or man, spreading spores of the fungus. Bird’s nest fungi are harmless, and raking prevents growth and movement of spores.

The artillery fungus, Sphaerobolus spp. may become problematic in mulch, due to the production and release of spores. This fungus produces very small, inconspicuous cup shaped fruiting bodies (about 1/10 of an inch) that contain a dark round spore body (peridiole). Accumulation of water and nutrients in the fruiting body eventually leads to a pressure release of the spore which is shot toward any light source up to a distance of several feet. Spores land on light colored siding, building foundations, or cars. Spots can be very unsightly and spore bodies have a sticky substance on them which can make removal extremely difficult. Soap and water with a scrub brush can be effective before material dries. Growth of artillery fungus is favored by hardwoods in mulch, excessive rainfall, or irrigation of foundation plantings.

Artillery fungus is problematic on north sides of buildings where shade maintains moist conditions. Use of mulch derived from dead and diseased trees should be avoided. Use of bark mulch or pine bark nuggets rather than hardwood provides a less favorable substrate. Addition of fresh mulch yearly can suppress fungi, but plantings should not be mulched too deep. Removal or raking of infested mulch to disturb growth of fungi may help. Research (D. Davis, PSU) indicates fresh mushroom compost blended with landscape mulch, at the rate of ≥40%, can be effective in reducing or suppressing artillery fungus, a good strategy in sites that have had artillery fungus. Addition of fresh mushroom compost adds organic matter, a rich dark color, and beneficial microbes that may compete with the artillery fungus.

Nancy Gregory, April 9, 2019

Disclaimer: Reference to commercial products or trade names does not imply endorsement by University of Delaware Cooperative Extension or bias against those not mentioned

This institution is an equal opportunity provider.

Applying Mulch Correctly

Properly applying or reapplying mulch materials can minimize or completely eliminate mold problems. Applying mulch loosely at a depth of 1.5 to 3 inches and no thicker prevents any portion of the mulch layer from the excessive drying that favors mold development. Watering dry or hot mulch that was bagged or piles in at the time of application so that both the mulch and the underlying soil are thoroughly moistened encourages the development of beneficial bacteria that compete with the fungi. Highly acidic mulch, which has usually undergone anaerobic decomposition and may smell sour, inhibits bacterial growth and can injure nearby plants.

Mulch Fungus: Why it Forms and How to Deal with It.

It’s gross. It’s ugly. It’s ruining your beautiful landscape. And no, it’s not the neighbor’s Pekingese.

It’s mulch fungus—an unattractive and unwelcome sight for many homeowners this spring. Known colloquially as “slime mold” and “dog vomit” due to its lumpy, often brightly colored appearance, mulch fungus can strike just about anywhere you spread mulch, and it’s common to Indiana.

The formation of mulch fungus happens in damp conditions as bacteria starts to feed on mulch. This is a microscopic process, but once fungi can feed on bacteria, they grow and create spores that eventually turn into clearly visible patches. While these patches are often yellow, they can be black, brown, white, orange, or even bright pink in certain cases.

Luckily, mulch fungus is not a serious problem. It poses little threat to plants since it feeds on bacteria, and it’s usually limited to small areas of your landscape. But it’s quite unsightly—and if you see it pop up in your mulch beds, you should get rid of it. It’s safe to touch, but you’ll probably want to get a shovel to dig it out. Make sure you scoop a few inches around the patch to eliminate unseen spores which can lead to a recurrence. Discard the fungus in a compost pile or in the trash—just make sure it’s far away from any mulch as spores can easily travel through the air.

Preventing mulch fungus is tricky, especially during wet spring months. But your best chance is to make sure your beds aren’t overwatered, and to water as closely to plant roots as possible. Letting a sprinkler water your entire flower bed all day creates an ideal environment for mulch fungus, so it’s better to use a hose or watering can to water plants individually when possible.

Another helpful tip is to give plants a significant watering once or twice per week (depending on precipitation) instead of watering them every day. A heavy watering will penetrate through mulch and get to roots more easily, while a light watering leaves much of the moisture stuck in the mulch—a perfect environment for mulch fungus. You might also want to rake your mulch at least a couple of times a month—especially during periods of heavy rain—to break apart fungus colonies.

If you’re having trouble with mulch fungus this year—or just need help improving your landscape with lighting, hardscaping, or beautiful plants—our team at Engledow would love to help. Contact us today to see what we can do for you.

Watch the video: Qu0026A - My Mulch Looks Like It Has Mold On It