Is My Compost Supposed To Mold? ( All The Facts You Need)





As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.

The world of composting is daunting for both beginners and experts. Although it seems quite simple in some ways – just wait for plant matter to rot down organically – it also has a lot that you will need to learn about it, and it’s natural to occasionally get concerned about what it is or isn’t doing.

One thing that many beginners feel uncertain about is whether they should be seeing mold in their compost heap, or whether that’s a sign that something has gone wrong. After all, in most parts of life, mold is not a good sign.

Mold is something you should treat with caution, but it’s not an immediate concern if you see mold in your compost pile.

Mold is often a natural part of food decomposing, and some food types are more prone to molding than others. Many compost heaps will contain mold without any negative impact.

Let’s explore what causes mold on compost, what “good” kinds of mold there are, and what might prompt a little more concern if you spot it in the heap.

mouldy lemon in a compost bin

What Does Mold In Compost Look Like?

You may already be familiar with many kinds of mold from food going off in the kitchen, but here’s what you’ll commonly see if your compost is going moldy.

Knowing the differences can help you understand your compost heap better, and will also let you know what to look out for. So, what are the common molds?

  • Green mold: the most common type for food compost, green mold is nothing to worry about. It will often occur if you have lots of food waste in your compost, as opposed to garden waste, but it isn’t a big problem or anything you should be too concerned about.
  • White mold: usually mold that appears on wood, white mold is a sign of positive decomposition and isn’t something to be concerned by.
  • Pink mold: this usually occurs if you have accidentally introduced household cleaning products to your compost heap. For example, if you discard soapy water on the compost heap, this sort of mold may start to develop.

You should deal with pink mold by not adding any cleaning products (directly or indirectly) to your compost heap.

Pink mold will kill off the bacteria that you need for a healthy compost heap, so it isn’t something you should ignore if you see it.

You shouldn’t need to actively remove it unless there is a lot, but take action to stop creating it.

Is Compost Mold Dangerous To Me Or My Pets?

Mold is something that we rightly treat with extreme caution. Mold spores are very easy to spread around and inhale, and you may not even realize that they are there, so be careful when turning compost that has mold in It.

Don’t let your pets consume anything from your compost heap, especially if it’s moldy.

However, mold from your compost is very unlikely to do you harm, even if you do breathe in some of the spores (try not to, though). It is just from decaying vegetable matter and shouldn’t hurt you.

If you are sensitive, however, it’s recommended that you wear a mask before dealing with compost that has mold in it.

Keep pets that are likely to investigate your compost away, even if your compost heap doesn’t seem very moldy. They still don’t need to be digging around and potentially eating old food.

If this is going to be a problem, consider a contained compost heap or fence it off. Although a small amount of mold probably wouldn’t hurt your pet, it’s better not to take the risk, and if they end up consuming a quantity, it could do them harm.

If you have added dairy or meat to your compost pile, be more careful for yourself and be vigilant about keeping your pets away from it.

Meat and dairy can grow much more harmful bacteria than vegetable matter, so try not to add these if you can avoid it, and treat them with caution.

Always wash your hands thoroughly with hot soap and water after handling your compost heap.

close up of mould in compost

What Foods Are Most Prone To Going Moldy Fast?

You might notice certain foods tend to mold much faster, so it’s worth thinking about what you’re adding to the heap. Rice, for example, molds quickly, as do bread, cereal, coffee, and spaghetti.

Rotten fruits and veggies also tend to mold, so don’t worry if you see mold clustering on old oranges or carrots.

It’s fine to compost foods that have already gone moldy, in case you’re wondering – after all, if the food can grow mold in the compost safely, you aren’t adding a risk by composting the already-moldy food.

In fact, you may even speed up your composting process, as you’re actively adding things that contribute to the breakdown of organic matter.

Will Finished Compost Have Traces Of Mold?

No, finished compost should not be moldy.

Everything that bacteria and microorganisms and fungi like to feed on should have been used up, and compost that is ready to use should look just like ordinary soil from your garden.

If you find that your compost is moldy in places, it is not yet ready for use on your garden, and could introduce things that might harm your plants – especially seedlings. Return it to the compost heap and let it process further.

man holding nose witha screwed up face indicating a bad smell

What If The Mold Smells Bad?

Moldy compost that smells particularly bad is something you should look out for. If it is also sludgy-looking, this could be a sign that anaerobic bacteria are growing in your compost heap.

Anaerobic bacteria don’t really pose a risk to you or your pets provided they aren’t being consumed, but they are a sign that your compost heap is not getting enough oxygen.

You should turn it and insert some sticks and other twiggy, dry matter to create air pockets. This should deal with the problem.

Should I Try To Prevent Mold?

No. As long as your compost heap is functioning and you are turning it regularly, mold is a perfectly normal part of the process, and you can just leave the fungi involved to get on with their thing.

They will break food down faster, aiding the worms and microbes that are working on it as well.

You probably couldn’t prevent mold from forming if you tried, so it’s best to ignore it.

If you are sensitive to mold spores, take precautions by wearing a mask when you’re handling the compost, and don’t let your pets get into the heap to eat leftovers.

If you really do want to try and reduce the amount of mold in your compost heap, letting it dry out a little and exposing it to direct sunlight are the best techniques.

This will discourage the fungi, which usually likes dark, cool, damp areas.

Do not use chemicals to get rid of mold in your compost heap, and don’t try natural remedies like white vinegar.

These will disrupt the balance of the heap and will kill off worms and soil microbes that are needed for compost to break down properly. You will essentially destroy your heap by adding this sort of thing.

women putting things to compost into a compost bin with a thought full look

What Organic Matter Shouldn’t I Add To My Compost Heap?

There are a few things that you should not add to the heap, especially if you plan to use the compost for growing edible plants.

These could introduce harmful bacteria to your compost heap, potentially much worse than mold.

Pet waste is a particularly big one. If your pet is carnivorous, their waste can carry bacteria and even viruses that could be very harmful to you.

Most home compost heaps do not get hot enough to safely deal with this, so don’t put pet poop in your compost.

Anything with insecticides or weed killer on should also be avoided.

These chemicals will mess with your compost heap (like the mold-generating-soap we discussed earlier) and could kill off the bacteria that the heap needs to operate well. They might also affect plants you use the compost on later.

Ashes from a barbecue or commercially-purchased coals. These can contain additives to help them burn that could be very bad for your compost. Ashes are good, but only if you know the source and it’s safe.


Mold in your compost heap is usually nothing to worry about at all. It is not dangerous to you or to your pets (though don’t let them eat it!) and won’t cause any problems.

As the compost decomposes naturally into soil, the mold should disappear anyway.

Mold is a natural aspect of the decomposition process, and can speed it up, particularly for certain foods.

It is part of a healthy, functioning compost heap, and while excessive mold or particularly bright mold could indicate a problem, white and green molds are not a cause for concern.

If you do see something that worries you, try to find pictures of it online and identify the specific kind of mold to set your mind at rest; there are lots of different types of mold, but most will not harm you just by taking up residence in your compost heap and munching through your food waste.

Related Posts

About the author

Latest Posts

  • Junk Food Compost: Turning Unhealthy Eating into Sustainable Fertilizer

    Junk Food Compost: Turning Unhealthy Eating into Sustainable Fertilizer

    Composting is a sustainable practice that transforms organic materials into a valuable fertilizer, benefiting both the environment and agriculture. This process involves the decomposition of brown matter, such as twigs and paper, green matter, like food scraps and grass, and the addition of water. By diverting waste from landfills and reducing the greenhouse gas emissions…

    Read more

  • Composting Bay Leaves: A Clear Guide to Effective Recycling

    Composting Bay Leaves: A Clear Guide to Effective Recycling

    Composting bay leaves can be an excellent addition to any home gardeners’ composting routine. Bay leaves, like other thick and leathery foliage, can provide essential nutrients to your compost pile and ultimately benefit your garden. However, it’s important to understand the specific characteristics of bay leaves and the proper methods for incorporating them into your…

    Read more

  • Will Compost Kill Grass? The Truth About Using Compost as a Lawn Fertilizer

    Will Compost Kill Grass? The Truth About Using Compost as a Lawn Fertilizer

    As a lawn care enthusiast, I have often heard the question, “will compost kill grass?” The answer is not straightforward, as it depends on several factors. Composting is an excellent way to improve the health of your lawn, but it can also damage it if not done correctly. Understanding compost is crucial to answering the…

    Read more

error: Content is protected !!