Why Does My Compost Have Mold?

Moldy compost with organic matter

Are you wondering why is your compost moldy? If you discover mold in your compost, try not to fret; this is a perfectly natural process that needs to occur for the organic material to decompose.

Having mold in the compost is the sign you are looking for because it means your compost is active and working correctly.

As a gardener of 5+ years, I always make my compost to feed my gardens. So, it’s time to share some of my secrets with you!

In this post, we’ll talk about how to make a great compost pile, what can and cannot go in the compost bin, and how to avoid having smelly compost:

Why do I have mold in my compost?

As new gardeners, we often think of mold as something that shouldn’t occur. We are often scared of mold because we don’t know what it could mean or how it affects our compost pile.

If you have decomposing matter in your compost such as leaves, woody material, or food, you will often see mold. All of these ingredients are called organic matter because they were once alive and can now be decomposed.

This mold isn’t necessarily bad. On the contrary, it means full decomposition is happening and the organic waste inside the compost bin is changing.

Is mold bad for compost?

Generally speaking, mold isn’t bad for your compost.

However, you must be aware of the different types of mold you could find in your compost. Sometimes you’ll see white or pink mold, whereas other times you’ll see a strong red or even green mold coming out of your compost. These are all good molds to have!

If you see green, slimy, and smelly mold continuously coming out of your compost, then something isn’t working right.

You should be concerned if your compost smells bad. If it stinks, it means something is not working as it should be, and you must reassess the way you are composting.

Perhaps your compost pile is too wet and you need to add more brown leaves or sticks, which bring carbon to the pile.

The mold’s textures could also change. For example, you could see how your compost has slimy or powder-like mold. These are all different types of fungi that could be active in the compost.

If you are worried about mold spores in your compost, you could wear a face mask when turning the compost. This way, you won’t inhale all the mold spores.

Can I put moldy food in compost?

Pile of compost in compost container

Yes, you can put moldy food inside your compost. You are going one step ahead by putting moldy food in your compost because the decomposition process has already begun. This is also a nice way to limit food waste.

You’ll also be adding new types of fungi to the compost, which could, in turn, mean that your compost will host a larger variety of beneficial fungi. Thus, your pile could decompose even faster.

However, there is one exception to this rule. You should never put moldy fish, meat, or dairy products into your compost bin. The reason behind this is that if you do so, you’ll be attracting unwanted pests to the composting facilities.

I usually bury any moldy fish or meats and plant a tree above the organic material. Albeit, this could only be done in big, open spaces.

Composting Best Practices

compost pile in a wooden compost container

Here are some basic requirements for you to make excellent compost:

Compost needs moisture

If you would like to have a successful compost pile, the most important thing to keep in mind is that your compost should always be moist, but not wet.

If the pile is wet, the organic materials will not decompose, and your pile could smell in no time.

On the other hand, if your pile is too hot and without moisture, you could inadvertently- killing kill microorganisms that are trying to live inside your compost bin.

You could also have smelly compost if the pile becomes too dry because oxygen won’t be able to move throughout the pile.

These microorganisms try to decompose all the organic material you put into your compost piles. So, ideally, you want to pamper them and keep them alive by having some moisture inside the compost pile.

And how do you know if your pile has enough moisture? Grab a sample with your hands and squeeze it.

If you feel it’s damp and water comes out of it, your compost is in great shape. If nothing comes out, your compost could be dry.

Compost needs oxygen

A good compost pile needs aeration. In other words, it needs to have enough room so air can flow and the ingredients ‘can breathe’ during the composting process.

You can work on the aeration in two ways: you could regularly turn your compost bin. By doing so, you will have two working bins instead of one so you can move your compost around.

The second way is to add larger wooden sticks that will, in turn, bring more carbon into the pile. By adding larger pieces of wood, you will create bigger inner spaces so there’s better air flow inside the compost.

Compost needs organic materials

Organic matter, whether moldy or not, are the basis of the compost pile.

Think of your compost in terms of the colors it needs. Organic materials should be green and brown, and your compost should have 50/50 of them.

Green ingredients are all the food you put in, all your garden weeds, and your lawn. Brown materials could be sticks, larger pieces of wood, and leaves.

The smaller the pieces you put in the compost bin, the better. This way, the materials will be able to decompose faster because the pieces have more contact surfaces with the air.


Compost wooden pannel

Is Compost Supposed To Mold?

Yes, compost is supposed to mold. Yet, too much mold could cause a problem because it means your compost pile isn’t balanced.

If you think your compost is too moldy (it is attracting too many insects, or you see a lot of green slimy mold), then your compost needs more air. You could remediate this by adding more carbon (or brown ingredients).


If you are wondering ‘why is my compost moldy?’, then you already know that your compost should be moldy. It means you are doing a great job at keeping all the bacteria alive and your compost is decomposing! Well done!

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