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Mold in Mulch? Here’s Why And How to Fix It

How to Fix Mold in Mulch

Moldy mulch is as gross as it sounds! It’s when fungi grow on organic mulch because of prolonged damp conditions and poor air circulation. 

To make things worse, the mulch also doubles as a food source for mold as it breaks down.

Luckily, you can fix this easily by reducing moisture and improving air circulation. This can be done by using less mulch, ensuring proper drainage, along with turning or fluffing your mulch every now and then.

If the problem persists, then you may want to consider using fungicides. Otherwise, you may need to consider alternatives to organic mulch that aren’t vulnerable to mold growth.

Why am I seeing mold in my mulch?

Why am I seeing mold in my mulch
Image: Rutgers Plant and Pest Advisory

1. Prolonged Damp Conditions

Prolonged Damp Conditions
Image: Rutgers Plant and Pest Advisory

Mulch that’s constantly damp is the perfect breeding ground for fungal growth. Moisture is a big factor because mold spores need moisture to germinate and form colonies.

The right amount of moisture and humidity create a conducive environment for mold to thrive and grow at a rapid speed. 

To boot, the growing mold has a steady nutrient source – your mulch – to support its growth. Hence, it’s only a matter of time before the mold takes over a large chunk of your mulch.

2. Poor Air Circulation

Poor Air Circulation
Image: Green Side Up Garden & Gifts

Another key factor for mold growth is inadequate air circulation. These little pockets of stagnant air in your mulch can result in moisture build-up which you already know is mold’s best friend.

Apart from that, they also create small spaces where humidity levels are high enough for mold spores to settle and grow. So if your layer of mulch is quite thick, then don’t be surprised if there’s poor ventilation. 

Having mentioned that, it’s worth noting that mold thrives in dark environments. With how much mulch you have, there are enough low-lit spaces for mold to grow rapidly.

What does mold on mulch look like?

What does mold on mulch look like
Image: Alliance Health

Mold on mulch typically has a fuzzy appearance with a fluffy and powdery texture. It also comes in different colors such as white, gray, black, and even green.

They have an irregular growth pattern which causes them to grow scattered and patchy. You may observe that some areas may be growing taller than others, creating miniature organic landscapes, if you will.

Another thing you’ll be able to notice is an earthy and musty odor, which is characterized by microbial activity related to the breaking down of organic matter. 

However, note that some molds may smell unpleasant or pungent, which could suggest that there’s more going on than meets the eye.

Is mold harmful to my plants or my family?

Is mold harmful to my plants or my family
Image: Backyard Neophyte Landscaping Blog

Mold on your mulch isn’t considered harmful to plants because it’s part of the natural decomposition process where fungi feed on decomposing organic matter. In fact, mold on mulch can actually play a role in improving the cycling of nutrients.

However, it’s a completely different story when it comes to your family, especially near young children, the elderly, and those with comorbidities. 

Excessive amounts of mold near living spaces could result in the following health risks:

  • Respiratory problems because of prolonged inhalation of mold spores, especially in people with respiratory conditions such as asthma or allergy.
  • Infections among individuals with weak or compromised immune systems.
  • Allergic reactions such as water eyes, stuffy or runny nose, sneezing, coughing, itchy throat, and irritated skin, to name a few.

How do you prevent mold on mulch?

How do you prevent mold on mulch
Image: HomeQuestionsAnswered

1. Use less mulch

Use less mulch
Image: goodwood

For mold to grow, it requires damp and humid conditions, which can manifest in thick layers of mulch that don’t get enough air circulating through. 

Having a layer of mulch that’s thicker than the recommended quantity could cause poor ventilation, trap moisture, warmth, and humidity, creating a conducive environment for mold growth.

Remember that mulch should only be around 2 to 4 inches thick, depending on the material, purpose, and climate. It should be spread evenly and fluffed to ensure there’s no compaction.

2. Ensure that there’s proper drainage

Ensure that there’s proper drainage
Image: Southview Design

Making certain that there’s adequate drainage helps prevent your soil from being constantly damp. The excess moisture is what creates a favorable environment for mold spores to grow and thrive.

There are several different ways you can create adequate drainage for your plant depending on where they are growing. 

Say, for pots you can ensure there are enough holes on the bottom while for raised beds you can add drainage materials in between layers for excess water to easily flow out from the bottom.

3. Turn or fluff the mulch

Turn or fluff the mulch
Image: The Morning Call

Fluffing your mulch periodically is key to ensuring that it’s aerated and evenly breaking down. Aside from that, mixing it helps to better disperse moisture along with incorporating the new mulch with the old, decomposing mulch.

Turning your mulch around also ensures that all parts get aired out and exposed to sunlight, inhibiting mold growth.

While you’re at it, regular inspection also helps to detect decomposition problems early on, giving you enough time for prompt intervention.

4. Use mold-resistant mulch

 Use mold-resistant mulch
Image: New Garden Landscape

Incorporating more mold-resistant mulch material can also help drastically reduce the likelihood of mold spores developing and growing. 

Certain materials are inherently more resistant to mold because of their properties such as containing natural oils, compounds, and texture.

Here’s a list of some mold-resistant materials that you can use or add to your existing mulch:

  • Stone
  • Gravel
  • Pine bark nuggets
  • Pine straw
  • Cypress
  • Rubber mulch
  • Untreated hardwood mulch
  • Cedar

How do you get rid of mold on mulch?

How do you get rid of mold on mulch
Image: Green Side Up Garden & Gifts
Speed●●○○○ | Fast
Difficulty●●○○○ | Easy
Things You NeedPlastic bag
Fresh and dry mulch

To get rid of moldy mulch, remove all contaminated mulch and replace it with new mulch that’s dry and fresh. While completely optional, you can also apply fungicide if the mold persists.

However, keep in mind that mold is completely normal and a natural part of the decomposition process. 

Nevertheless, here’s a quick and easy-to-follow guide on how to remove mold from your mulch!

What To Do
1. Using a shovel, scoop out the contaminated mulch. 
2. Dispose of the contaminated mulch by placing it inside a plastic bag and discarding it in the trash.
3. Apply fungicide as directed in the instructions. 
4. Using a trowel, rotate the mulch to ensure that all areas have been evenly coated with the fungicide.
5. Add new, fresh, and dry mulch.
6. Turn and fluff the mulch with a trowel to mix in the new mulch.


How does mold in mulch spread to other plants?

The spores of mold can primarily spread through water, air, wind, and be transported by small animals like insects. 

Can mold spread to other parts of my garden?

Mold spores can spread to other parts of your garden, especially if conditions are favorable for them to thrive and grow.

Does mold also grow during the winter months?

It’s possible for mold to grow during the winter months, but they’ll be less active because of the cold temperatures. However, if conditions are still damp then they could grow year-round.

Is mold harmful to plants?

Generally, mold isn’t harmful to plants because it only feeds on decaying organic matter. However, the conditions that require mold to grow and thrive are harmful to your plant as its environment needs to be excessively damp and humid with limited air circulation.

Can I add moldy mulch to my compost?

Adding small amounts of moldy mulch to your compost is perfectly fine, especially if you turn your mulch regularly. 

However, adding large amounts of heavily contaminated mulch may ruin the composition of your compost. Thus, it would be better to dispose of it through other channels.

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