Mold in Worm Farm – Is a Moldy Worm Bin Harmful? (What to Do)

Mold in Worm Farm blog banner

Worm farms are a great way to compost kitchen waste and other organic matter.

The worms consume the waste and generate worm castings that are rich in nutrients, making them an excellent amendment for garden beds. But worm farms can be susceptible to molds!

In this article, we’ll discuss the causes of mold on worm farms and whether or not you need to worry about them.

We’ll also be listing some tips on how to deal with it and what to do in case of mold overgrowth.

And if you’re wondering if molds are harmful when it comes to worm composting, read on, but first let’s answer the question in short before going into more detail:

Mold can occur in a worm bin for a number of reasons, including poor ventilation, too much moisture, increased acidity in the environment, and either too much or not enough food.

Here’s a deeper look into why your compost bin is getting moldy and how to fix it:

Why Is My Worm Farm Moldy?

Molds are beneficial microbes when it comes to worm farm ecosystems.

They contribute to the composting process by breaking down organic matter into rich nutrients that can be used to fertilize plants.

Molds can also aerate the soil and control certain kinds of pests.

Here are some conditions that favor mold growth:

Poor Ventilation

Poor ventilation is often the cause of mold in worm farms.

If the farm is not adequately ventilated, the system becomes stagnant, anaerobic and humid, creating favorable conditions for mold growth.

This can also cause worms will suffocate and die.

And when they die, the food scraps will also rot, which creates a more optimal environment for mold to thrive.

Too Much Moisture

If you notice that your worms are becoming paler and thinner, these can be indications that there’s excess moisture in the worm bin.

While a little bit of moisture is essential for healthy worming, too much moisture can create an ideal environment for mold spores to take hold.

Also if there is too much moisture where worms live, it can cause them to escape or ultimately, drown.

The Fix: Add a thick layer of shredded junk mail (no colored inks!), newspaper or other carbon sources to soak up excess water.

Increased Acidity

A pH level between 6 and 7 is ideal for farming compost worms.

Though worms are tolerant of acidic conditions, acidic environments are also the natural breeding grounds for molds to thrive.

Too Much or Not Enough Food

If there is too much food waste, the worms will not be able to eat it all before it starts to rot.

On the other hand, worms die if they don’t have enough food.

And when they die, they will rot along with the worm food you’re putting in the worm bin.

This again creates conditions that are favorable for mold growth.

Does Mold Harm Worms?

If you’re new to worm bins, seeing mold might seem scary. Or, you might wonder why mold is such a big deal.

After all, isn’t mold just a natural part of the decomposition process?

As we said earlier, mold is often present in worm farms or compost systems as it helps break down food and other organic matter for worms.

And while it’s true that mold is often present in worm farms or compost systems, too much mold can also take over your worm bins and cause harm to your worms, often indirectly.

They may attract fruit flies, pests and other critters.

They can even start to compete with your composting worms for food.

So it’s best to keep the mold growth at a minimal level to keep them from competing with your worm population.

Besides the worms, mold can pose a serious health risk to people allergic to it.

Mold spores can cause respiratory problems, skin irritation, and even immunosuppression in some people..not what you need while vermicomposting!

How Do You Fix a Moldy Worm Farm?

Let’s look at a number of ways you can limit mold while you are worm composting:

Increase Ventilation

Make sure that there is plenty of airflow through the worm farm.

You can do this by drilling small holes on the sides of the bin or using a fan to circulate air if need be.

Also, when wrapping your worm farm during the winters, ensure you’re not restricting ventilation.

Reduce Moisture

To correct the moisture level of your worm farm, simply reduce the amount of water you’re adding to the farm.

If the drainage holes are not working, remove the blockages.

Add more dry bedding material such as soil, straw, shredded cardboard, coffee grounds and shredded newspaper to soak up some moisture.

In the meantime, you should also reduce adding food scraps with high water content until the moisture level is corrected.

Increase pH Level

Molds thrive in acidic environments.

So by increasing the pH level, you can control the overgrowth of mildew in a worm compost bin.

You can add lime to your worm box regularly to raise the pH and make it less hospitable for mold spores.

Remove excess food waste which may be fermenting in the worm bin.

You may also decrease feeding your worms with acidic fruits such as oranges and tomatoes.

Add Fresh Bedding Layers

Mix up your worm farm bedding to distribute the patches of mold growth until they disappear then add new bedding layers.

By doing so, you can reduce mold growth.

Maintain Feeding Your Worms with Just the Right food supply

The key is to maintain a balance and geed your worms the right amount of food.

Add food a little at a time.

Too much food waste for the worms to consume will often turn into moldy food in your compost pile.

You can also monitor your worm’s eating habits and then feed them accordingly.

Red worms/red wigglers/tiger worms are among the more voracious eaters and can handle more food but you are still at risk of overfeeding.

Mold in Worm Farm blog post image

Night crawlers like African night crawlers will get through food less quickly.

If food is being left over and you have the space in your vermicompost bin, try to add worms.

On the flip side, if there are too many worms in your worm bin, add more food so they can survive and provide you with more finished compost and worm castings.

Don’t Add Foods That Mold Easily And That They Won’t Eat

Certain foods are harder to break down and digest for worms which means a more moldy bin.

Foods like:

  • Dairy products
  • Meats

aren’t recommended.

Keep Your Worm Farm Out of Direct Sunlight

The heat will cause worm feed to decompose and spoil faster which could cause more mold and other organisms in your bin.

Your red wigglers or nightcrawlers also won’t appreciate extreme heat boiling up their bedding. They could try to escape or worse, die.

Type of Mold in Worm Farms

Blue Mold

Blue molds cause fruit and vegetable spoilage so it’s not surprising to see patches of blue molds in your worm bins every now and then.

As they are often found on rotting food, this may indicate that you’re putting too much food in the worm bin.

Green Mold

Green molds are commonly seen growing on fruits, bread and other foods.

They can also thrive on the top layer of worm bins if given the proper living conditions such as too much moisture and poor ventilation.

Some subspecies of green molds emit mycotoxins that are toxic to people so you may want to be careful with them.

(Not So) Fun-Fact: Green-Black mold spore is considered one of the most dangerous molds due to the deadly mycotoxins that they produce.

Slimey White Mold

Slimey white molds don’t pose much threat to both humans and worms.

These kind of slime molds are usually present in compost piles and almost everywhere outside your worm bin.

Overall white mold won’t harm your buddies in your worm factory.


Mold in worm farms is a common occurrence.

By ensuring that the farm is adequately drained and ventilated and that the worms are properly fed, you can help prevent mold from taking hold.

If mold does start to appear, it may be due to too much moisture or insufficient ventilation in the worm bin.

And if there’s an overgrowth of mold in your worm farms, you can take some simple steps to prevent further growth.

Generally, mold will not harm your worms, but if you’re allergic to them, you might as well get rid of them.

Too much mold growth can also harm your compost worms.

Have you ever started a worm farm, only to find that it’s become moldy? If so, what did you do to take care of it?

Also Read: