Why Is Fungus & Mold Growing In My Mulch (And Should I Remove It)?

If you’ve found fungus (which causes mold) growing in your mulch, you may be wondering what the cause is, whether it is bad for your garden, and how to get rid of it.

While fungus can be an eyesore, it’s important to understand that it’s not necessarily harmful to plants.

Indeed, the biggest reason for removing fungus is because of its unappealing appearance.

Does Mulch Cause Fungus

Does Mulch Cause Fungus

Mulch is an excellent addition to any garden.

While mulching your plants can bring a number of benefits, such as improved moisture retention and soil aeration, too much of anything has its risks.

Specifically, mulch that is too deep or damp can act as a hospitable environment for unwanted fungal growth.

This is because fungus loves to grow in dark, moist environments. Mulch also provides plenty of organic materials for the fungus to feed on.

Mold usually grows in mulch when it is warm (between 77 and 86 degrees Fahrenheit) and when there is enough moisture in the air. You’ll typically see mold and fungus in your mulch growing during the warm and wet summer months.

Is Fungus Mulch Bad For My Mulch And Garden?

While fungus can be unsightly, it’s important to remember that it’s not necessarily bad for your mulch or your garden.

In fact, many types of mold and fungus can actually help break down organic material in the soil and improve its nutrient levels.

Mold is a naturally occurring element of decomposition, so it makes sense that it appears quite commonly when using mulch.

That said, if you’ve got large patches of fungus growing on top of your mulch, you may want to take steps to remove it as it doesn’t look particularly attractive and can spread quickly.

The Most Common Types Of Fungus Mulch

The Most Common Types Of Fungus Mulch

While there are over 140,000 species of fungi, we can generalize that there are four types of fungi that will grow in your mulch.

They include mushrooms, slime molds, artillery fungus, and bird’s nest fungus.


This is a type of fungus that you’ll commonly find growing in mulch. Specifically, a mushroom is the reproductive structure of some species of fungi.

They can appear in a variety of sizes and colors. Mushrooms aren’t harmful to your mulch or garden, but beware that some of them can be toxic.

If you have children or pets playing in your garden, it may be safer to remove these mushrooms.

Slime Molds

Slime mold also referred to as ‘dog vomit’, is a group of single-celled organisms that live in damp or wet areas. They are not considered true fungi but are closely related to them. Slime molds usually grow on decaying wood and other organic matter. Hence; they usually thrive in particularly damp areas on your mulch or on rotting tree branches and logs.

Slime molds are usually yellow or brown but can sometimes be bright orange or even blue.

Slime mold is not bad for your mulch or plants. In fact, they help break down dead plant matter. The main reason to remove this mold is that it can ruin the aesthetic appearance of your garden.

You can remove most of this mold by using a broom or raking it away. Otherwise, you can let it undergo its own lifecycle. By the end of this cycle, it’ll have become a powdery consistency that can be easily washed away with a hose.

Artillery Fungus

Artillery fungus is a common name for any species of fungi belonging to the family Lycoperdaceae.

Artillery fungus can range in color from white to pinkish-brown, and its fruiting bodies are small, oval-shaped, cup-like structures. When these spores are ejected, they resemble specks of dirt or a shot of gunpowder.

The name is derived from the way in which the spores are ejected, resembling a small artillery shell. Artillery fungus can be found growing on decomposing wood, mulch, and other organic materials.

When mature, the fruiting body of an artillery fungus produces a white spore mass, which when dry, is forcibly ejected from the cup-shaped structure in a series of multiple bursts. This ejection can propel the spores up to several meters away from their origin, allowing for wide dispersal.

The presence of artillery fungus can be an issue for homeowners and gardeners as the ejected spores are dark brown or black and can stain windows, outdoor furniture, and other surfaces with which they come into contact.

Like many fungi, artillery fungus isn’t bad for your mulch or garden and it cannot be eliminated completely. Using bark mulch or straw mulch to cover this fungus will help prevent it from spreading and staining the surrounding area.

Bird’s Nest Fungus

This is a harmless and non-toxic type of fungi that – as the name suggests – looks like a bird’s nest.

This fungus consists of many small cups that are roughly the size of a dime, each holding spore-containing bodies that appear as eggs.

Role of Spores in Fungus Growth

Fungal spores are a key component in the life cycle of fungi. Fungal spores allow fungi to reproduce and spread.

Spores are microscopic and can be airborne, easily landing on mulch and other surfaces. When the conditions are right, particularly in the presence of moisture and suitable temperatures, these spores germinate and grow into new fungal organisms. The different types of fungi have varied methods of spreading their spores.

For example, stinkhorns use their foul smell to attract insects that help disseminate their spores, while bird’s nest fungi use raindrops to splash their spore-containing structures to new locations. Artillery fungus is known for its ability to shoot spores into the air, which can stick to nearby surfaces.

How To Prevent Mulch Fungus From Growing

How To Prevent Mulch Fungus From Growing

Fungus loves to grow in damp and dark areas.

It makes sense that mulch that is usually in the shade will have more fungus growing in it than mulch that is exposed to more sunlight.

But if exposing your mulch to more sunlight isn’t an option, there are many other effective things you can do to slow down the growth and spread of fungus.

The spread of fungus can be prevented by turning your mulch with a rake every so often. Aerating helps prevent moisture buildup, improve oxygen flow, and disrupt fungus that is beginning to take hold in your mulch.

If you want to take things further, you can also apply a fungicide that is designed specifically for controlling mulch fungus.

Adhering to a stricter watering schedule and maintaining a fresh layer of mulch can also work wonders in preventing fungus growth in your garden. If you water mulch every day, then you are not giving it enough time to dry out. Instead, aim to water your mulch 2 – 3 times every week so it has enough time to dry out and not stay damp.

When you do water your mulch, don’t be afraid to water it heavily to ensure the moisture gets to the roots of the plants beneath the mulch.

Lastly, some mulches have stronger antifungal properties than others. In general, softwood mulches like cedar mulch will prevent fungal growth more than hardwood mulches.

Removing Existing Fungus From Mulch

As we have already identified, most mold or fungus that grows in mulch is safe and a natural part of mulch decomposition.

Many people, however, dislike the way fungus looks and how it can detract from the visual appeal of your garden. Therefore; removing existing fungus may be the best option to restore the pristine look of your garden once more.

Fungus cannot survive without water, so one option is to dry out the mulch. This is possible if you have direct sunlight on the mulch for a few days and there is no rain.

The bad news is, there’s nothing much you can do to control the weather, and your mulch still needs water to feed the plants beneath it.

Vinegar can also work well to remove mold and fungus. Its acidic composition will work to break down the mold after a few applications. However; be sure not to spray this on your plants, as vinegar will be harmful to them too.

You can dilute the vinegar with water to make it less potent. This will make it less dangerous to your plants but also less effective against mold.

The best recommendation we have for removing fungus is to take it out by hand.

But be careful when you do this, as you don’t want to play a part in spreading the spores of the fungus to other parts of the garden. You also don’t want to inhale the spores, especially if you or someone else suffers from allergies or any other respiratory issues.

To be as safe as possible, wear gloves and a mask. Then place a plastic bag over the fungus and dig it up from below, into the bag. Tie the bag up and dispose of it correctly in the bin.

Using Baking Soda as a Natural Fungus Remedy

Using baking soda as a natural fungicide for plants has become increasingly popular among gardeners. This method is attractive to those seeking less harmful solutions to combat fungal problems in their gardens.

The effectiveness of baking soda as a fungicide works best as a preventative measure against fungal diseases.

While it can also eliminate existing fungal issues, its success rate is highest when used preemptively.

Typically, the mixture for this fungicide involves baking soda, water, and occasionally mild or insecticidal soap to help the mixture stick to plant leaves.

It’s important to apply this solution during cooler parts of the day, such as dusk, to prevent potential leaf burn. The mixture should be used promptly after preparation, as it doesn’t have a long shelf life.

Baking soda operates by creating an alkaline environment, which is unfavorable for fungal growth. Most fungi thrive in acidic conditions, so altering the pH with baking soda can inhibit their growth.

However, frequent application could lead to bicarbonate buildup in the soil, potentially disrupting nutrient uptake and hindering plant growth.

There are alternative recipes and combinations available for using baking soda as a fungicide. Some variations may include combining baking soda with vegetable oil, dish soap, and water. Other recipes might suggest adding vinegar or Murphy’s oil soap to get rid of fungus in mulch. These mixtures can be used on a variety of plants, but it’s crucial to test them first, as some plants may react negatively to certain ingredients.

Despite being a safer alternative to chemical fungicides, baking soda should still be used with caution. Overuse can alter the soil’s pH and potentially harm plants. Therefore, it’s advisable to closely monitor your plants and stop using the solution if any negative effects are noticed.

Understanding the Benefits and Risks of Bleach in Mulch Fungus Removal

Understanding the Benefits and Risks of Bleach in Mulch Fungus Removal

One method often discussed to combat mulch fungus is the use of bleach.

One of the benefits of using bleach for mulch fungus removal is that bleach acts as a potent fungicide, effectively killing fungi and other microorganisms in the mulch. It also works quickly to eradicate fungal growth, providing almost immediate results. Additionally, bleach is easily accessible and cost-effective compared to specialized fungicides.

However, there are risks and considerations to bear in mind.

The health of the soil can be negatively impacted by bleach, as it may exterminate beneficial microorganisms that are essential for a healthy soil ecosystem.

If used improperly, bleach can be harmful to plants, possibly causing leaf burn and potentially being lethal to young or sensitive plants. There are also environmental concerns to consider.

Although bleach breaks down into salt and water, the process can release harmful chemicals into the environment, which can harm wildlife and contaminate groundwater. Furthermore, handling bleach requires caution due to its corrosive nature, which can cause skin irritation and respiratory issues if inhaled

If you decide to use bleach for mulch fungus removal, there are some best practices to follow.

  • Always dilute bleach with water, with a common recommendation being one part bleach to nine parts water.
  • Apply the solution directly to the areas affected by fungus, and avoid over-spraying onto plants or soil.
  • Wear protective gear, including gloves and a mask, when handling bleach.
  • Consider using more environmentally friendly alternatives like vinegar or baking soda solutions, especially in gardens with delicate plants.

Compost and its Role in Preventing Fungal Growth in Mulch

Compost plays a significant role in enhancing soil health and can be particularly effective in preventing fungal growth in mulch.

Fungi are more common in mulch made from fresh hardwood bark and ground wood, which contain high concentrations of cellulose that decompose readily.

To reduce fungal problems, it’s recommended to use composted mulch, which is prepared by adding nitrogen sources like grass clippings, poultry manure, or urea, and then composting the mix for a minimum of six weeks.

Compost enhances soil fertility and structure, promoting healthy plant growth.

The microorganisms in compost break down organic matter, releasing essential nutrients into the soil. This process enriches the soil, replenishes nutrients, and supports sustainable agricultural practices. Compost also helps in maintaining optimal soil pH levels, acting as a natural buffer. This is crucial as extreme soil pH levels can hinder nutrient availability and uptake by plants. Moreover, compost improves the soil’s water retention capacity, reduces the need for irrigation, and serves as a natural pesticide and disease suppressant​​.

However, once the composted mulch cools after being applied, it can still potentially support nuisance fungi. Moisture content, temperature, and pH levels of the mulch influence the likelihood of fungal colonization. Maintaining the moisture content above 35% and avoiding overly deep application (more than 4 inches) can help minimize these issues​​.

Common Misconceptions and Myths About Mulch Fungi

Mulches’ interaction with fungi often leads to a proliferation of myths and misconceptions, causing unnecessary worry among gardeners and homeowners. The mysterious world of fungi, with its diverse forms and behaviors, intertwines with mulch in ways that are often misunderstood. Let’s dispel some of these misconceptions.

Dispelling Myths Surrounding Mulch Fungus

There are several misconceptions about mulch fungi. For example, it’s a common belief that all fungi need oxygen to grow, but in reality, some anaerobic fungi can grow in environments without oxygen. Another myth is that all bracket fungi on trees indicate a dying tree, which is not always true, as some form symbiotic relationships without causing harm.

Impact of Mulch Fungal Growth on Wildlife and Pets

Generally, mulch fungi are not harmful to pets or wildlife. The primary concern with pets relates to cocoa bean mulch, which can be harmful if ingested by dogs due to its chocolate content. Other common mulch fungi, like stinkhorns and slime molds, are mostly harmless to animals​.

Understanding the Difference Between Harmful and Beneficial Fungal Growth in Mulch

Not all fungi in mulch are harmful. Many, such as bird’s nest fungi and certain mushrooms, play a beneficial role in decomposing organic matter. However, some like the artillery fungus, can be problematic due to the staining spores they release.

Debunking Popular DIY Methods for Mulch Fungus Removal

Popular DIY methods for controlling mulch fungus, such as using baking soda or vinegar, may not always be effective. Adjusting the pH of the soil can impact plant health. It’s important to understand that fungal growth is a natural and often beneficial aspect of mulch decomposition.

Evaluating the Long-Term Effects of Mulch Fungi on Garden and Landscaping

Over the long term, mulch fungi contribute to the decomposition process, enriching the soil. While they can sometimes be unsightly or cause minor problems like staining, they generally do not have a negative impact on the overall health of gardens and landscaping. Fungi can play a crucial role in nutrient cycling and soil health​.

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