Can Composting Start A Fire? ( A Detailed Guide)




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If you’re just getting into gardening and starting with your “green thumbs”, you might be noticing that there are a lot of things to learn, and some of them sound quite daunting.

Though compost heaps are relatively straightforward once you’ve got them up and running, they come with a steep learning curve and can be tricky to manage at first.

If you’ve ever come across the idea of a compost heap catching fire, it might both puzzle you and put you off composting for life.

After all, it sounds pretty dangerous, especially in the summer, when many gardens have lots of dry kindling around.

Here are some basic facts about how compost heaps can catch fire and the best ways to prevent this from potentially happening.

Why Do Compost Heaps Catch Fire?

Compost heaps generate a surprising amount of heat, especially in the summer.

The microbes which are responsible for the breakdown of food and garden waste create heat, and this often ends up trapped right at the center of the heap.

Coupled with plenty of sunlight, especially in summer, and you might be amazed by how hot your compost heap can get.

This heat is useful in that it helps the compost break down faster, but it can also present problems.

Firstly, excessive heat will kill off the good bacteria which is keeping the compost heap balanced and functioning – but more significantly, in some circumstances, it can present a fire risk.

Compost heaps often have pockets of air in them, caused by the sticks and woody material that make up a healthy compost heap. These pockets provide the oxygen necessary for flames to take.

Let’s be clear that compost heaps catching fire is not a very common occurrence at all, and you don’t need to panic and dash outside with the hose.

It’s unlikely to happen, but it’s still worth being aware of the risk so you can mitigate it, especially if temperature levels climb in the middle of the summer.

The phenomenon of compost heaps catching fire is called spontaneous combustion, and it can lead to smoldering heaps which, under the right conditions, can burst into full flame.

This usually happens in commercial compost heaps that are not being managed properly, but it is still worth being aware of the danger and how to minimize it.

What Conditions Must Be Met For A Compost Heap To Catch Fire?

A fire needs three different conditions to be met in order for it to start in a compost heap. Firstly, the heap must be fairly dry, with air pockets as a result of sticks, twigs, etc.

A wet compost heap shouldn’t be a fire risk.

Next, there must be an uneven distribution of moisture in the heap, with some parts dry and other parts wet. This might happen if you have added material from different parts of your garden.

Finally, a compost heap needs to be large, and the outside of the heap must be insulating the inside, limiting the airflow and trapping the heat in.

Small compost heaps aren’t likely to pose a fire risk as they simply don’t get as hot inside.

women holding grass smiling

What Else Increases The Risk Of A Fire?

Another thing which you might be doing that increases the risk of your compost heap catching fire is adding a large amount of nitrogen to your bin all at once.

Nitrogen is found in grass clippings, food scraps, coffee grounds, and greenery.

In the summer, you’re more likely to be adding grass clippings to the heap in large quantities, so bear this in mind.

Make sure you are also adding brown waste, such as twigs, dry leaves, cardboard, etc.

Precautions You Can Take

This is definitely a case where prevention is better than cure, so take a look at the following tips for reducing the fire risk – and you won’t find yourself hosing down a smoldering compost heap!

Position The Heap Away From Flammable Material

Before you build a compost heap, it’s worth thinking about its positioning. It’s a good idea to build compost heaps away from wooden structures such as fences, and also away from the wall of your house.

This will mean that if they do catch fire, there isn’t too much for them to burn, so the fire shouldn’t be able to spread.

If you have built your compost heap near a fence or another flammable source and you also live in a hot part of the world, consider moving it.

This might be a nuisance, but it’s important to mitigate fire risks wherever you can, and if the surrounding area offers lots of fuel for a fire, it’s better to be safe than sorry.

Don’t Make Massive Heaps

Big compost heaps trap the heat much more effectively, so they are a far bigger fire risk. If you have a lot of garden waste to compost, think about making several separate heaps, and don’t let any of them get too big.

Compost piles that are bigger than 12 feet high are probably getting dangerous, and it’s better to split these into two or more separate piles.

Monitor The Temperature

Obviously, keeping an eye on how hot the compost heap is getting allows you to recognize when risks are climbing, and take action.

You should measure the inside of the heap, not the outside, as most of the heat will be trapped within.

During the summer, taking regular readings from your compost bin will help ensure you are aware if it’s getting too hot – both for the microbes and for the safety aspects – and then you can start taking steps to reduce the heat, which we’ll move onto now.

Checking the temperature frequently will encourage you to keep a general eye on the compost heap; this will give you early warning if there’s any sign of smoke, or if you smell burning.

A healthy heap should be between 100 degrees F and 160 degrees F.

Keep Turning The Compost

Regularly turning your compost heap is an important part of maintaining it – you should be doing this for lots of reasons, but reducing fire risk is one of them.

Turning a compost heap usually means taking a garden fork and using it to stir, lift, aerate, and generally disturb the materials inside the heap.

This is a good way to break up pockets of waste that aren’t decomposing properly, to distribute microbes throughout the heap, and to keep things ticking along.

However, it’s also important for reducing the risk of a fire.

You can empty your compost bin onto a tarpaulin and then tip it back into the bin; this is probably the easiest way to turn it, unless you have a tumbling compost bin.

This will let the heat disperse, help distribute moisture more evenly, and break up any pockets of material or air.

It’s crucial to the health of your compost heap anyway, so you should be doing it irrespective of the fire risk.

Turning the pile also increases the airflow, stopping the material inside from clumping up and forming mats with uneven distributions of air and water in them.

Water Your Compost

We all know the best way to combat fire is with wet material.

You don’t want to turn your compost heap into sludge by constantly soaking it, but wetting the contents down from time to time will help to keep it active, and will reduce any chance of a fire starting.

Many people simply add a little water every time they add a layer of compost.

If you have emptied your bin out, pouring water on the contents as you return it to the bin will help to keep everything nicely damp.

What To Do If A Fire Is Starting

If you find your compost heap smoking, don’t panic, and don’t immediately start tearing the pile apart to get at the source.

Adding a sudden flow of oxygen to the smoldering pile could cause flames to flare up, and might make things a lot worse.

Always call the emergency services if you are worried about a fire getting out of hand, and never take unnecessary risks.

However, if you are able to address the problem safely yourself, start by hosing the pile down, and then slowly remove a little at a time, continuing to soak it as you go.

Once you’ve finished, let everything cool down, and then use the above steps to reduce the chance of another fire occurring, decreasing the size of your pile, checking it more often, and increasing the ratio of brown waste in your bin.


Domestic compost heaps are unlikely to catch fire in normal circumstances, even in summer.

However, it is worth knowing the risks and how to reduce them.

It’s also important not to let your compost heap get too hot if you want the microbes in it to keep working effectively, so paying attention to temperature is beneficial.

Remember to check on and turn your compost heap regularly and stop it from getting too big to manage, and you shouldn’t have any problems with fire or even excessive heat in your heap.

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One response to “Can Composting Start A Fire? ( A Detailed Guide)”

  1. […] pits and add the ash to your compost pile instead. This is a great idea if you’re having a fire or if you have a wood burner of some sort, but might be fiddly for everyday use. However, the ash […]

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