How To Get Rid Of Mold In Mulch? Complete Step-by-Step Guide

Helen Skeates
Helen Skeates
29 min read

For those of you who spend a significant amount of time in the garden, you’ve definitely wondered how to eliminate mold from mulch. It’s an ugly sight that’s bad for the environment and the health of the plants around it.

The good news is that you may safely eliminate this from your yard by following certain measures. In addition, you’ll discover how to stop it from spreading in the future.

Why Is My Mulch Moldy?

Mold thrives in moist, dark, and well-ventilated areas.

  • Mold feeds on organic matter (wood chips are a favorite!).
  • Defintion (if you get lots of rain or if you over water)
  • Intimacy (temperatures of 77 to 86 degrees Fahrenheit, or 25 to 30 degrees Celsius, seems to be perfect for mold growth)

Wood chips are a popular landscaping accent for many homeowners.

Slime Mold on mulch - YouTube

Instead of wood chips, gardeners have a variety of other options for mulching their gardens.

  • Compost
  • Chopped-up grass
  • Leaves that have fallen on the ground.
  • needles from the pine tree
  • Paper
  • Cardboard

Mold can grow on any of these materials if the conditions are correct.

Mulch has a number of advantages in the garden and landscape, among them are:

  • Thermodynamics (keeping soil from heating up or cooling down too fast)
  • retention of water (preventing water from evaporating out of the soil)
  • prevention of weeds (smothering existing weeds or stopping the growth of new ones from seed)

Organic materials such as wood, plant fibers, or paper are commonly used to make mulch. Mold thrives on organic material like this one.

Mold can’t grow on organic material by itself, of course. Mold can only grow if the mulch or the surrounding environment is sufficiently damp (from rain or irrigation).

Mold thrives in a warm, moist environment. Mold thrives in environments with temperatures between 25 and 30 degrees Fahrenheit.

In the spring and summer, after a few days of rain, you’ll see mold on mulch. Increasing temperatures and extended periods of damp mulch increase the likelihood of mold formation.

Check out the EPA’s page on mold for more information.

What Is Mulch?

Mulch is a type of soil amendment that is applied by spreading or laying it on top of the soil. This is most commonly used by gardeners to conceal exposed dirt in flower beds and gardens.

A wide variety of mulches are available for purchase and use. Both organic mulch and synthetic mulch are included.

The types of organic mulch are the following:

  • The types of organic mulch are the following:
  • The following are some examples of organic mulch:
  • Chopped-up grass
  • Recycled leaves
  • Straw
  • Newspapers

A synthetic mulch:

  • Plastic in the color of night
  • The fabric of the landscape
  • Stone
  • Gravel

To protect the soil from excessive sunshine, mulch serves as a natural fertilizer because it is organic and decomposes easily. Slower decomposition of drier and woodier mulches, as well as a decreased supply of nutrients to the soil, is the result.

Mulch has several uses in the garden and landscape, and one of the most important is to block off direct sunlight.

  • Insulation
  • Retention of water
  • Prevention of weed growth

Mulch might contain hazardous weed seeds, so it’s important to know where you’re obtaining it from. Chemicals can also contaminate your vegetation, so be sure to check your mulch.

Why Does Mold Grow On Mulch?

Fungus, often known as “slime mold,” forms on mulch when it’s wet and the bacteria begin to eat it. Mold spores are dispersed by the larger molds as they mature, resulting in yellow, brown, black and white patches of mold that can be seen in the vicinity.

Mold thrives at temperatures between 77 and 86 degrees Fahrenheit. In order to put an end to the growth, you must remove the roots and dry them out using vinegar or other home remedies.

Mulch fungus is generally not harmful and is not a major issue, but it should still be eradicated if possible. Sometimes, spore masses with foul scents are produced, which might draw insects and flies.

How Does Mulch Mold Spread?

Even though mold can easily spread on its own, there are some outside conditions that can help it expand even more. Consider the following aspects:

  • Insects
  • Water
  • Wind
  • Animals
  • It’s the movement of mulch by nature.

Using these ingredients, mold spores can move from one location to another, where they can then begin a new growth cycle.

You should not permit these forms of mold growth if you have pets because it can cause disease and even death due to poisoning. To avoid this, learn how to keep animals away from plants.

What Does Mold On Mulch Look Like?

Depending on the type of mold, mulch can take on a variety of distinct looks. The following are some examples of possible mold colors:

  • white
  • black
  • brown
  • orange
  • yellow
  • green

White rings, orange, yellow, or brown spots may appear on the mulch’s surface.

More information on forms of mold that develop on mulch can be found in this article from UMass Amherst.

Many different kinds of mold and fungi can grow on mulch. Starting with “shotgun” fungus, below are some examples.

Shotgun Fungus (Artillery Fungus)

Generally speaking, shotgun fungus is not damaging to plant life. An orange or cream colored “cup” contains a black spore cluster.

The spore clump here resembles an egg. The cup will eventually explode, dispersing the spores over a distance of up to 12 feet, allowing them to colonize additional mulch or soil.

The black spores released by the exploding egg can stain automobiles and houses, so take caution! Using a mixture of 40 percent spent mushroom compost and landscape mulch has been found to be effective in suppressing artillery fungus.

The Penn State University Extension has an excellent piece on mold that you might enjoy.

Slime Mold

Slime mold, due to its look, is also referred to as “dog vomit” by some. Any bright hue will do, from yellow to orange.

Slime mold, on the other hand, is not a mold at all, despite its deceptive name. Slime mold is thought to be descended from ancient amoebas, according to the University of New Hampshire Extension.

Although slime mold isn’t dangerous, its color contrasts well with black mulch, making it an unappealing addition to the landscape.

Slime mold can be learned more about by reading the Wikipedia article linked above.

Bird’s Nest Fungus

Small, egg-filled nests of fungus resembled by the name of Bird’s Nest Fungus. A rainstorm causes “eggs” from the “bird’s nest” to spread fungus.

When it rains, bird’s nest fungal spores disperse.

Generally speaking, Bird’s Nest Fungi pose no threat to plants.

Check out this Wikipedia article on Bird’s Nest Fungi for more details.

Stinkhorn Fungus

An foul odor emanates from the stinkhorn’s cap. As they fly away, the stinkhorn’s spores are carried by the flies.


A mushroom is nothing more than the underground fruit of a fungus. The spores are contained in this fruit, allowing the fungus to multiply and spread.

Your plants will not be harmed by mushrooms. However, some of these plants can be toxic to humans and animals, so keep an eye out for youngsters and pets!

Check out Wikipedia’s page on mushrooms for more information.

How Does Mold Spread?

Mold can get into your mulch in a variety of ways, including:

  • water
  • insects
  • animals
  • wind
  • Mulch movement

Rain or water can help spread various molds, such as bird’s nest fungi, as previously indicated. In order to avoid the spread of mold using this method, do not sprinkle your mulch with water if you notice mold on the surface of it.

It is possible for insects or animals to carry mold spores. Stinkhorn fungus spores, for example, are frequently disseminated by flies.

It is possible for mold spores to travel through the air. Mold spores, like dandelion seeds, can travel through the air in search of new soil or mulch to colonize.

Finally, if the mulch you purchase already contains mold spores, it may spread the mold. As a result, the mold is likely to grow if you water your plants frequently or if it rains frequently.

Buying mulch from someone who removes unhealthy or dead trees increases the risk of mold spores being present in the wood chips.

Is Moldy Mulch Harmful To Plants & Trees?

There is little danger to healthy plants and trees from most mold. When trees and plants are dead or have fallen, mold will grow on them and begin the decomposition process.

The plants in your yard are more susceptible to mold if they lack nutrients or have been overwatered.

Mulch does not often require any special treatment to prevent mold growth. Mold is a natural feature of the decomposition of wood and other organic materials.

Mulch should not be placed too close to plants or trees if mold growth is a concern. Avoid covering the base of your plants or trees with mulch.

Mold spores from the mulch will not be splashed onto your plants if this is done.

Slime Mold on Mulch - Green Side Up Garden & Gifts

How Do You Get Rid Of Mold On Mulch?

If mold on mulch is an issue for you, there are a few options available, including:

  • Dehumidifying the area (not practical in all climates)
  • Using vinegar to clean it (simple, but may harm nearby plants)
  • Taking it apart and putting it out of use (requires the most work)

By the way, cedar mulch, which is resistant to rotting, can be used to replace wood mulch to minimize mold and decomposition.

It’s possible that your mulch already has mold on it. In that case, let’s take a closer look at mold removal procedures.

Drying Out Mold

In the absence of any water, mold will not grow, according to the EPA. However, removing the sources of moisture that mold thrives in is not always simple.

You can, of course, use a watering can or a drip irrigation system to water your plants. Overwatering from a sprinkler can be avoided this way.

You can, however, do little about a prolonged period of rain or extreme humidity. Otherwise, see if any of the other options on this page work.

Treating Mold With Vinegar

Vinegar is an easy approach to get rid of mold. Spray the mold with vinegar after filling a spray bottle with it.

Many varieties of household mold can be killed by vinegar, according to Healthline. Even yet, it doesn’t completely eliminate all molds.

Acetic acid in the vinegar is expected to weaken and finally kill the mold because of its acidity. However, it may take a few applications of vinegar to get the desired results.

Keep in mind that vinegar’s acidity can be both a blessing and a curse. Your plants will die if you spray them with acidic vinegar, so don’t do it!

If you’re concerned about the vinegar’s acidity, you can dilute it by adding water.

You can also experiment with changing the pH of your soil to either a more acidic or basic state to prevent mold growth. A soil’s pH can be lowered by adding sulfur (sulfur dioxide) and raised by adding lime (calcium carbonate).

Mold can be killed by an excessively high or low soil pH, but it may also affect surrounding plants and trees.

Using acidic soil to kill mold can be accomplished by planting blueberries or azaleas there. It is possible that these plants can grow in areas where other plants would not.

Digging Up & Disposing Of Mold

Digging out and disposing of mold is one last option for eradicating it. But there are a few drawbacks to this approach.

If the mold is developed, moving it could disperse the spores. In the long run, this can worsen your mulch’s mold problem.

In order to avoid this, place a sack over the mold before digging it out (preferably a biodegradable one). In addition, it makes it simpler to transport the mold after it has been dug up.

Mold spores can also be inhaled when performing this type of work. Mold exposure can trigger cold-like symptoms in some people.

Asthma and allergy sufferers are particularly vulnerable to this. Because of this, it’s important to wear a face mask when excavating for mold.

Final point: mold can settle everywhere, even if you don’t disturb the air with its spores when moving it. In order to get rid of it, you’ll need a technique to dispose of it.

Mold can thrive in locations you wouldn’t think, as it doesn’t require light to flourish.

Is Mold In Mulch Dangerous To Plants?

Mulch mold, as previously stated, poses no health risk. Even if you don’t want to, you can touch it without fear of punishment.

The white mold, on the other hand, is harmful to plants since it is a mold that is toxic to them. To learn more about the causes of white mold on plants, see this page.

People who are allergic to mold may experience health problems as a result of exposure to mold in the landscape. Stinkhorns and other mushrooms, on the other hand, can be harmful if eaten.

How To Remove Mold From Mulch

You have three options for getting rid of mold and preventing it from returning to your mulch. Among them are:

  • A process of evaporation
  • Adding vinegar to the water
  • removing the soil’s roots

Method #1. Drying out the mold

It’s important to keep in mind that this approach won’t work in all conditions. The soil in humid locations is more prone to retain moisture and water.

You can destroy any mould already present in the mulch by allowing the growing area to get completely dry. To avoid damaging your plants, only water them when absolutely essential.

Method #2. Using vinegar

To begin, prepare a vinegar-to-water solution by mixing equal parts vinegar and water. Make it easy to apply by putting it in a spray bottle.

Vinegar’s acidity has the potential to weaken mold structure and, in the long run, to kill the organism. Mold removal may take several attempts, as this is not a quick fix.

While vinegar is effective at killing most molds, it can be hazardous to some plants as well. Avoid spraying directly on or near any of your plants.

Method #3. Digging up the roots

Mold in mulch can be removed using this procedure, which is both effective and safe. In order to avoid breathing mold spores and innocuous chemicals, ensure that you have the right protective gear on before you begin.

If you’re going to remove mature mold from mulch, you should cover it with plastic both during and after removal to prevent it from dispersing further spores into the air.

After you’ve removed the mold, make sure you clean the area thoroughly. It’s tempting to ignore mold and fungi because of their vibrant hues, but doing so can be dangerous.

Can Old Mulch be Mixed into the Soil?

The organic matter in the soil can be increased by incorporating old mulch into the soil.

But there is one thing to keep in mind when doing so:

Microorganisms and bacteria degrade wood chips by consuming nitrogen from the soil, resulting in a nitrogen shortage in the soil at first.

This would temporarily deplete the soil’s nitrogen supply, harming the plants already there. Yellowing of the leaves is an indication of nitrogen deficiency, which is caused by a lack of chlorophyll production.

Ammonium ions are formed as a result of the breakdown of organic matter by decomposers. The nitrifying bacteria subsequently convert the ammonium to nitrates.

Depending on the soil’s state and microbe population, this procedure can take anywhere from two months to six months. Â Â

Decomposition requires nitrogen, which is absorbed by microorganisms and released into the soil as ammonium nitrate.

Once the wood chips have been broken down, the plants will flourish.

Anaerobic breakdown of mulch can occur if there is insufficient oxygen in the soil, resulting in strong odors.

See our page on why soil smells unpleasant for more information.

If you’re in need of new mulch, I’ve found a wonderful deal on a high-quality product that I’ve used myself.

What are the Benefits of Mixing Old Mulch into the Soil?

Adding old mulch to your garden soil has numerous advantages. Adding organic matter to the garden is a good thing, but it’s not the only benefit.

As it decomposes, old mulch releases beneficial bacteria and fungi into the soil.

Increases Organic Matter

Compost made by microbes and bacteria contains a lot of organic stuff. As a result, the soil’s natural community of beneficial flora and fauna benefits from a healthier and more disease-resistant plant population.

Increase Drainage and Aeration in the Soil

Soil drainage can be improved with the use of compost. When the mulch is broken down by microorganisms and bacteria, the compost is formed.

The soil’s natural population of beneficial plants, such as earthworms and insects, will benefit greatly as a result of this. As they move through the soil, these creatures contribute to the creation of air gaps and the improvement of soil drainage.

Increase Nutrients In the Soil

When mulch is added to the soil, it provides a feast for soil bacteria and microorganisms. The mulch will contribute nutrients to the soil, which will benefit the plants in the long run.

See our thorough article on how mulching can improve soil organics and microbial health by increasing the soil’s organic matter.

How to Till Mulch into the Soil

This requires a shovel.

Mulch should be buried as deeply as possible in the soil without causing damage to the roots of your plants. The most important thing is to avoid mulch clumping in the soil.

  1. Remove any extra soil mulch (This is to prevent nitrogen deficiencies)
  2. Till the first 2 to 4 inches of topsoil using the leftover mulch you dug up with a shovel.
  3. Soil should completely cover the previous lot.
  4. Compost organic material as a final layer.
  5. Distribute the compost over the soil in a symmetrical fashion.
  6. Spread a thin layer of fresh mulch over the compost that has just been added.

Adding mulch to the soil is a great idea – Twigs and branches that have fallen from trees and plants commonly make up old mulch.

The Amazon mulch that I’ve used and tested is a good option at a reasonable price.

Is Old Mulch Bad for Plants?

Mulch is frequently misunderstood as harmful to plants. Mulch can actually be beneficial to plants if you use the right sort and apply it correctly, but this is not always the case.

Old mulch can be incorporated into the soil, where it will decompose and provide nutrients to the plants. A new layer of mulch can be placed on top of the old one, or it can be left alone during that process. Old mulch decomposes over time and eventually becomes part of the soil.

Slime molds

Mulch can benefit plants by :

  • With severe rain, snow, or drought, nutrients can easily be washed away from the soil.
  • Anti-weed and grass-killing measures.
  • Reducing the soil’s heating-causing UV radiation.
  • Increasing soil drainage and aeration by retaining water.

For gardeners who wish to create an eye-catching landscape, an appealing façade, or a safer environment for their home from pests such as fire ants, mulch can be a useful tool.

Inorganic mulch, if used, should be avoided since it does not improve soil drainage or aeration and hence should not be mixed with the soil.

Our recommendations for mixing old mulch in the Soil.

  • Don’t overdo it when it comes to combining ingredients ( prevent nitrogen deficiencies)
  • Compost the mulch that was taken
  • To ensure that old mulch decomposes, mix it in before the winter freezes over.
  • When adding mulch to the soil, only use organic materials.

Types of Garden Mulch

There are two types of mulch for gardens: organic and inorganic.

Organic Mulches

You can increase the fertility of your soil and the growth of your plants by using organic mulches, which decompose over time.

Inorganic Mulches

Rubber mulch and landscape cloth are examples of inorganic mulches, which are comprised of synthetic materials. Learn how to remove old landscaping fabric from the soil by reading our article on the topic.

In the event that the mulch breaks down, the chemicals contained in it could harm plants if they get into the soil.

It’s also possible that the chemicals will make their way into your food. As a result, you should only use organic mulches in your landscaping, and being aware of the type of mulch you have will help you avoid problems down the road.

Types of Organic Mulches

  1. Nuggets, Chips, or Bark
  2. Straw
  3. Cardboard or Newspaper
  4. Clippings of Grass
  5. Chips of Cocoa
  6. Coffea Slurry

Types of Inorganic Mulches

  1. Fabric for Gardening
  2. Mulch of rubber
  3. Stone or rock Mulch

Too much Mulch can be Bad for Plants

Mulch with rock or stone.

Choose a mulch that will break down over time if you do decide to use it; otherwise, it will be difficult to spread.

When mulching soil, keep in mind that each type of soil has its own characteristics. Consider using a mixture of wood and other garden products, including compostable materials, to help your plants grow more quickly.

Insects and rodents will have a place to nest and hide if you mound mulch around your plants.

To avoid evaporation, too much mulch may cause the soil to hold surplus moisture that would otherwise have evaporated from the surface. In the long run, this might lead to root rot and other plant issues.

Can I Mix Mulch with Potting Soil?

Do not use potting soil that has been polluted with insecticides or fungicides when mixing mulch into the soil.

Plants may be harmed by these chemicals.

In addition, you should incorporate mulch into your potting soil in smaller amounts and allow it to decompose over time. The plants will be protected from pests, and sufficient drainage will be provided.

The time given for the modest amount of mulch to break down in the potted plant will minimize the occasional nitrogen deficiency associated with increased bacterial activity from the breakdown of the mulch.

Do not add any inorganic mulch to your potting soil, since this will have no positive effect on your plant’s growth.

Potted plants should only have decorative inorganic mulch on top of them.

Our in-depth essay on the advantages of covering potted plants with rocks can be found here.

Do I Need to Remove Old Mulch before Adding New Mulch?

Before adding new mulch, you don’t need to remove the old one. However, you must make sure that the overall mulch mass does not form a barrier to the soil below when additional mulch is added.

If the mulch is overly thick, the soil will retain more moisture and heat, both of which are undesirable on hot days.

For the best results, you should mix some mulch into the soil and remove the remainder, which can be composted for future use, to prevent the formation of a soil barrier.

Will Weeds Grow through Mulch?

Mulch can occasionally allow weeds to grow. To prevent weeds from tunneling through mulch layers, make sure that the mulch is equally distributed on all sides of your garden bed or potted plant.

Mulches such as Stonewool, lava rocks, pebbles, or cordwood can also kill weeds, so keep that in mind as well.


Why do I have mold in my mulch?

In moist environments, the growth of mulch fungus occurs as bacteria feed on the mulch. When fungi are able to feed on bacteria, they proliferate and produce spores that eventually form visible patches. It’s difficult to prevent mulch fungus during the damp spring months.

Does mulch mold go away?

If you’re looking to give your garden a polished look while also keeping weeds at bay and retaining moisture, consider using bark mulch. Mold and fungi in mulch are generally safe, but if you take some extra precautions when spreading the mulch, you can get rid of them without having to buy new mulch.

Should you remove old mulch every year?

So, do you think it’s time to get rid of the old mulch? Experts in the field of gardening say that removing the mulch from last year’s plants is a waste of time. Over time, the organic matter in mulch breaks down, releasing nutrients into the soil. Removing mulch every year is a waste of time and money, and it’s not necessary.

What is the white stuff under my mulch?

When you put organic matter in the bed, the white stuff grows on it and breaks it down. Known as saprophytic fungi, these organisms do neither harm or infect plants. Animals graze on decomposing organic materials, such as mulch, compost, soil conditioner, and other similar products.

How do you remove mold from bark mulch?

The fungi can be killed by heating the mulch to 110-140 degrees Fahrenheit. Simply rake the mulch when it has been completely watered, and you’re done.

Is moldy mulch bad?

Plants are generally unaffected by moldy mulch. Avoid overwatering your plants during rainy periods to avoid excess moisture buildup around the plant.

What does bad mulch look like?

Yellowing leaves, scorched-looking foliage, diminished vigor, and even death of the plant can be signs of this process. You can keep your mulch fresh and fragrant for months if you store it in a well-ventilated and dry environment.

How do you clean old mulch?

Make sure to avoid any seedlings or shoots coming from the soil while you brush away all the mulch, dead leaves, and cut bits of edge. If there is no fungal development in your garden, scoop up all the waste with a shovel and dump it into your compost pile.

Can you till mulch into soil?

In order to boost organic matter in the soil, it is possible to add old mulch to it. In addition to improving the soil structure and providing nutrients for plants, the aerobic decomposition of mulch by bacteria and other microorganisms also increases drainage and aeration for plant roots.


Getting rid of mold in mulch isn’t as difficult as you might think. There are a few things you can do on your own if you don’t want to hire a professional.

Helen Skeates

Helen Skeates

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