Can a Compost Pile Catch on Fire?

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can a compost pile catch on fire

A landscaping company in our town recently experienced a bad fire and we learned it originated in their large piles of organic matter. This caused my wife and me to wonder if our own compost pile could ever catch fire, so I did some research to find out.

So can a compost pile catch on fire?  In the right conditions, a pile consisting of organic matter can catch on fire, most commonly due to spontaneous combustion. It is more common for this to happen for large commercial compost piles. It is rare for a small compost pile used by a home gardener to ever catch on fire.

Even though I found it to be rare for my own compost pile to ever catch on fire, I still wondered how this could actually occur and what I could do to prevent it. We’ll answer those questions and more as you read on in this article!

What Conditions Would Cause a Compost Pile to Catch on Fire?

Improper maintenance of a compost pile could potentially cause it to overheat and catch on fire. Many of the following conditions would need to occur in order for this to happen:

  • Dry material
  • Biological activity
  • A large pile that is well insulated
  • Material that is non-uniform
  • Dry pockets of air
  • Untouched pile for a significant time to allow it to heat up
  • Improper moisture distribution

Again, based on my research these conditions would be difficult to be met in a small compost pile for your home garden. The kind of piles that can spontaneously combust are large masses of organic materials used by commercial composting and landscaping operations. These companies can sometimes leave large piles unattended for long periods of time in hot and dry climates. This can be dangerous and cause a serious fire, which happened in our town to one of our landscaping companies!

Even though it is rare for this to happen in my own small compost pile at my house, it is still important to know how to tell if my pile is getting too hot and what I can do to prevent these conditions from occurring.

How Can I Tell if my Compost Pile is Too Hot?

I like to monitor the temperature of my compost pile with a compost thermometer. As you can see in the picture above, I stick the long thermometer into the middle of my pile of organic matter and leave it there at all times. This lets me know if my compost pile is active enough to speed up the composting process so I can get finished compost as quickly as possible!  

My pile is easily over 140 degrees Fahrenheit after maintaining and turning it properly. If the pile is getting up to the 200-degree range or higher, this is when a gardener should start being concerned. It still may not mean a fire will occur, but at this temperature, the risk of killing all the good biological activity in the compost is high. These microorganisms are hard at work breaking down organic material so they need to stay alive!

Another common sign that compost might be too hot is if a large amount of nitrogen is added to the pile. Nitrogen comes from green material such as fresh grass clippings, coffee grounds and food scraps. With an improper balance of nitrogen to carbon, a pile could start to overheat.

What Can I Do to Prevent my Compost Pile From Overheating?

A number of steps can be taken to maintain a compost pile correctly. This will ensure that your pile does not get too hot where it might kill all of the living creatures that are working to break down material (or worse yet, catch on fire), but also keep your pile hot and active enough that these same creatures can work hard to create finished compost fast!

Avoid excessively large piles.  While your compost pile needs to be at least 1 cubic yard (3 feet by 3 feet by 3 feet), it should not exceed 12 feet high.

Frequently keep an eye on your pile.  Don’t neglect your pile. If you see any smoke or smell something that is burnt, your pile may be too hot.

Turn and mix up your compost pile frequently.  By using my compost thermometer, when I see that my compost is cooling down and no longer in the active temperature range, I know it’s time for me to turn my pile. It’s as simple as moving the pile out of your bin/spot and then moving it back.

Water the layers of your compost pile.  Dry conditions is one of the factors we listed above that could cause a fire. Water is necessary for the living microorganisms to survive and break down the material.  Whenever I create or turn my compost pile, I water the material in layers as I build it up.

Add the proper amount of green and brown material.  Most information out on the internet will tell you a proper brown (carbon) to green (nitrogen) ratio is around 30 to 1. Do I measure this out when I create my pile?  Definitely not! You don’t need to be that particular about it. Just know that you need a lot more brown material than green material.  

Make sure you have proper air flow.  If a pile is too dry, good air flow could be a bad thing if it causes dry pockets of air in the pile. However, with the right amount of moisture, good air flow is essential for the living microorganisms to thrive. Turning compost will automatically improve the oxygen in a pile because it prevents the material from getting matted down. You can also create your pile in an open container such as wire mesh, chicken wire, or pallets. Below is a picture of my double bin compost pile created from free pallets.

Check out our Best Compost Products page for all of our tips on how you can start composting yourself!

“In peace I will lie down and sleep,
for you alone, Lord,
make me dwell in safety.”

Psalm 4:8

Related Questions

How do I put out a fire in my compost pile?  If it is an emergency, call the fire department. Otherwise slowly remove and spread out the cooler outside parts of the pile, applying water to the layers as you go. Do not aerate the pile too quickly because oxygen will fuel the fire.

What causes compost to heat up?  Chemical decomposers such as bacteria, fungi, and actinomycetes work hard to break down organic matter in compost piles. Their chemical processes produce acids, carbon dioxide, and heat.

What is the ideal temperature for a compost pile?  Your compost pile will be most active at temperatures between 100 and 160 degrees Fahrenheit.

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Corey Leichty

Hi, I’m Corey and I love using gardening as a way to provide food for my family, learn life lessons alongside my wife, Andrea, and teach life lessons to my two sons. Do you have gardening questions? Not finding what you are looking for? Please feel free to Ask a Question (Click Here!) and I will get back with you as soon as I can!

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