How To Get Rid Of Fungus In Mulch

Bark and woodchip mulch is a favorite ground cover for planting areas within and around the lawn. It insulates ground temperatures, keeps in moisture, and breaks down slowly over several years. These same features, however, can make mulch a good growing environment for fungus or fungal colonies when conditions are moist. 

With some regular attention throughout the year as part of normal yard maintenance, fungal growth is easy to prevent. With that same attention, you’re able to catch any growth that does get through before it spreads too much.

What Causes Fungus On Mulch?

Although it breaks down very slowly, woody mulch is organic matter that eventually is decomposed and integrated into the topsoil. As the mulch settles over time, it’s broken down by bacteria and provides the nutrients that fungus needs to grow. Wood mulch is different from grass compost or vegetable compost as it is very carbon-rich (which fungus prefers) and very low in nitrogen. 

Mulch is good for woody plants like trees, shrubs, and already mature plants since the fungal growth in wood-based soils helps support the slow-growing roots of established annuals and perennials. Seeds and herbaceous plants like grass and vegetables don’t grow well in mulch since there aren’t enough nutrients available as they need, and the weight of the woodchips prevents seedlings from sprouting and emerging. This is why it makes such a good ground cover for areas where you don’t want grass or weeds to grow.

The dark and moist environment, firm support, and lack of competition allow fungal spores that drift through the air and land on the mulch to settle and grow. Two of the most common fungal growth in backyard mulch are slime mold and artillery fungus.

Is Fungus On Mulch Harmful?

Is Fungus On Mulch Harmful

Most kinds of fungal growth on mulch aren’t harmful but are a nuisance. Slime mold, also known as “scrambled eggs” or “dog vomit” is a yellow, yellowish beige, or orange-colored fungus that spears in small masses on top of mulch. Like many other mushroom species, it’s not harmful to people, pets, or plants, but it is unsightly. It’s also a sign that the mulch is retaining too much moisture.

Shotgun fungus, on the other hand, also isn’t harmful, but it can make a mess that stains. This fungal growth, also known as artillery fungus, is a beige mass that, once it reaches maturity, will burst to expel its spores. The fungus’ 20 foot radius means that if it’s too close to your home or car, it leaves small black dots that adhere to the surface and are difficult, or impossible, to remove. 

How To Get Rid Of Fungus From Mulch

Fungus can be easy to get rid of as long as you don’t smash it. If you step on it or scrape it with a rake, you can send the spores soaring. If you see a cloud of powder escape, it’s the fungus’ spores being released.

They can, however, be picked up by hand by lifting from the bottom. The fungus is moist and compact when it’s fresh, but as it dries out, it gets more fragile and closer to releasing its spores. Using a shovel works as well: digging from underneath, the fungus can carefully be scooped up and disposed of. 

How To Prevent Fungal Growth In Mulch

White Mushroom

Like weeds, fungus grows (or grows back) if the growing environment isn’t monitored or maintained. Since fungal spores are drifting across yards regularly, incorporating a few tactics into your yard care routine will keep the unwelcome growth at bay. If you have a particular problem with fungal growth in your location, a combination of these strategies would be most effective. 

  • Aerate the mulch – Since mulch is an organic ground cover, it starts to compact as it gets rained on and breaks down over time. This is when the moisture and nutrients really start to support fungal growth: they like the damp, warm, and dark conditions that mulch provides. When you aerate by mixing the mulch around once a month with a garden fork or rake, the well-aerated woody mulch keeps the environment dry and cool.
  • Add new mulch – Mulch’s conditions will degrade over time as it decomposes and gets eroded by rain, so adding a fresh layer now and then will help keep the materials solid and better able to drain moisture and hold air. Like raking and disturbing sitting mulch, new mulch creates a less favorable growing environment for fungus.
  • Use fungicide – Using a fungicide is an option that lets you keep your mulch and prevent unwanted growth. Copper based fungicides are a popular option to prevent growth of fungal diseases on plants and can be used in light applications on your mulch. Mixing some baking soda into your mulch is another option since it raises the pH, or the alkalinity, of the mulch. Fungus likes acidic soil, and some types of wood mulch, especially pine, raises the ground’s acidity. Despite this preference for acidity, pouring undiluted vinegar on fungal growth that you catch in its early stages will kill it, as will a boiling gallon of water.
  • Plant more plants – Another strategy to keeping mulch fungus out of your yard is by planting more plants in your mulched areas. Shrubs, bushes, leafy vines, and some flowers have dense foliage that can help keep spores from landing on your mulch. Any fungus that might grow under those plants would also be blocked from spreading, as the leaves provide a solid barrier to the release of spores.
  • Consider mulch alternatives – A last option to dealing with fungal growth in mulch is to opt for another ground cover. Using gravel, paving, or other rocks; extending your lawn, and planting hedges or other plants where your mulch would be all remove the inherent risk of fungal growth that a mulch groundcover poses.