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Can Mulch Get Moldy? (And Will the Mold Harm Plants?)

Can Mulch Get Moldy? (And Will the Mold Harm Plants?)

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Mulch is beneficial to plant growth as it plays a vital role in soil enrichment.

Layering mulch on your plant’s soil helps retain moisture and regulate temperature. Mulch is also essential in keeping weeds away from your plants.

However, insufficient care can result in the unsightly growth of molds, especially on organic mulches.

These unwanted growths often appear slimy and yellowish, with some molds presenting as white, fuzzy rings or brown patches. At times, molds on mulch give off a stinky smell too.

While most mold growth on mulch doesn’t present a significant risk that may eventually result in plant death, knowing how to maintain your mulch properly is essential in keeping it presentable.

Let’s learn the different techniques to prevent mold growth on mulches, how to fix moldy mulch, and the different types of mulch that are less prone to mold growth.

Will Moldy Mulch Harm Plants?

Finding molds on the surface of your mulch is quite common. Given the mulch’s organic composition and moisture-rich quality, it’s no surprise that molds grow on them.

However, moldy mulch isn’t harmful to plants; it poses little to no risks to their well-being and growth. The only disadvantage, though, is that mold growth can ruin the appearance of your landscape.

Also, the presence of molds in your mulch can be an indication that you’re overwatering your plant.

Why Does My Mulch Get Moldy?

Mulch can be made with nutrient-rich organic or inorganic matter and functions as an insulator.

Aside from keeping your plants healthy, mulch is a good landscaping element that makes your garden soil look presentable.

Having unpleasant mold growth on your mulch can be pretty upsetting. Aside from mold, other fungi, like oyster mushrooms, also grow in mulches.

Meanwhile, here are the contributing factors of mold growth in mulches:

1 – Excess Moisture and Humidity

Molds thrive best in humid and damp environments, and an overly wet mulch is the ideal breeding ground for these organisms. Ideally, a humidity level of 70% and above favors mold growth.

Overwatering your plant and excess rain are two leading causes of increased moisture in mulches.

2 – High Temperatures

Warm temperatures up to 86°F support mold growth. Mold spores spread quickly in warm temperatures. In fact, a combination of a warm and moisture-rich environment is optimal for mold growth.

3 – Too Much Organic Matter

Organic mulches, especially those containing compost, wood chips, or chopped leaves, easily harbors molds. This is because molds source nutrients from organic matter and decaying materials in the soil.

What Is the Mold That Grows in Mulch?

Here are the two most common types of mold you’ll find on your mulch:

Slime Molds

Slime mold is the gooey mold commonly infesting bark mulches. It first appears like yellow to orange slime, strongly resembling animal puke or scrambled eggs.

Eventually, the slime mold turns into hard, dark-colored, and powdery growth. This type of mold usually appears after periods of heavy rain or during wet weather.

Interestingly, these molds can grow on plants without harming them. The only disadvantage is slime molds on plants can limit photosynthesis by blocking light.

Saprophytic Molds

Another mold growth we can observe in mulches is saprophytic fungi that appear white, fuzzy, and crumbly on the mulch’s surface.

The saprophytic mold breaks down decaying matter and usually doesn’t harm plants. This type of mold is common on compost mulches.

While these molds look displeasing, they can support plant growth by breaking down organic material and releasing essential plant minerals.

Can Moldy Mulch Be Used?

If you have a mold problem in your mulch, tossing it out and replacing it with a new one isn’t always necessary.

Yes, it’s perfectly safe to use a moldy mulch. But if you’re concerned with its unpleasant appearance, several techniques exist to eliminate it.

How to Remove Mold Growths From Mulch?

Did you know that getting rid of moldy growth on mulch doesn’t have to be expensive?

Spare yourself the hassle of running to your local store and use readily-available household items you can find in your pantry.

Here are some methods to get rid of mold on your much:

1 – Remove and Dispose of Affected Areas

This method only applies if the mold growth is small and not yet mature.

Since molds spread through spores that penetrate the air, digging out and transferring mold-affected portions may result in mold growth in other areas of your garden.

On the other hand, you may need to discard heavily-affected mulch entirely.

2 – Spray Affected Area With Vinegar and Water Solution

The vinegar’s acidity is effective in minimizing molds on mulch.

To make a vinegar solution, dilute one part of vinegar to four parts of distilled water and spray directly on affected areas.

Only use white vinegar or apple cider vinegar because some vinegar variants can be highly acidic and harm your plants.

3 – Spray Lemon Juice Solution on Moldy Mulches

A lemon juice solution is an excellent alternative. Mix equal parts of lemon juice and water and transfer the solution to a spray bottle.

4 – Use Organic Fungicides

Organic fungicides are environment-friendly, not to mention that they’re safe for humans and pets too. Examples are neem oil and horticultural oil.

5 – Mix Baking Soda and Water to Combat Mold Growth

Did you know the baking soda solution effectively removes mold on mulches? Add two tablespoons to a gallon of water and pour it on the affected areas.

6 – Make a Cornmeal Solution and Spray It on Moldy Mulches

To make a cornmeal solution, mix up to 240 grams (or 16 tablespoons) of cornmeal in a gallon of water and spray it on mold-infested portions.

Does Mold Growth Resolve on Its Own?

Mold growth on mulches, especially slime molds, usually disappears without intervention.

Usually, it can take up to three weeks until the mold disappears entirely. Exposure to intense sunlight is one reason why molds disappear in no time.

How Can You Prevent Mold Growth in Mulch?

Proper plant maintenance is essential in preventing mold growth in your mulches.

That said, avoid overwatering your plants, as the excess moisture favors mold growth. Did you know you don’t need to water your plants daily?

It’s best to establish a regular schedule for watering your plants (depending on their water needs) or wait until the upper layer of the soil is dry before watering them again.

Regularly raking your mulch is also an effective method of preventing mold growth. Raking prevents moisture retention as it exposes some mulch particles to the air, thus, drying them out.

What Types of Mulch Are Less Prone to Mold Growth?

Are you tired of treating mold growth in your mulches? To end your struggle with mold growth, switching to mulch varieties less prone to mold is best.

For example, molds don’t usually grow in inorganic mulch like those made with gravel, rocks, and rubber.

These options also incorporate an aesthetically pleasing vibe to your garden. However, the only disadvantage is that they’re much more costly than their organic counterparts.

At the same time, softwood bark and cedar mulch are resistant to mold growth too. They’re much cheaper than gravel, so they’re a good choice for those who want to save some bucks.

Final Thoughts

The slime mold and saprophytic mold are two common variants affecting mulches. These molds usually affect organic mulches like those made from bark and leaves, which are most prone to molds.

While moldy mulches are unsightly, they aren’t harmful to plants. In fact, some may resolve on their own after up to three weeks.

Lastly, regularly raking your mulch is one effective way to prevent mold growth.


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