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Why Landscaping Mulch Can Spontaneously Combust—and How to Prevent It


Most people don’t think “fire hazard” when they think of mulch. However, that’s exactly what your mulch can be if improperly applied.

If you’ve never heard of mulch fires or spontaneous mulch combustion it can sound made up. Sadly, mulch fires are very real, but there are things that you can do to prevent them, like being careful with where you place your mulch, how you care for it and what kind of mulch you use. We spoke with two fire experts about what causes mulch fires and how you can prevent them from happening in your own yard.

What Causes Mulch Fires?

There are two beliefs about mulch fires out there. The first is that mulch can spontaneously combust causing fires. The second—and most widely believed—is that mulch catches fire due to improperly discarded smoking material.

Spontaneous mulch combustion is believed to happen when heat builds up within a thick layer of mulch, say six inches or more. Theoretically, if enough heat builds within that layer, it can start to smolder and cause a fire. Although not extensive, there is some research supporting that mulch can spontaneously combust in certain atmospheric conditions.1

"The latter theory of mulch fires being caused by improperly disposing of flammable material, like cigarettes, is more plausible," said Michele Steinberg, Wildfire Division Director of the National Fire Protection Association.

“Mulch may not burst into flame at the touch of a cigarette, but it can and does smolder, and fire can creep along under mulch beds and erupt long after the initial ignition as humidity drops and wind picks up,” she said.

How to Prevent Mulch Fires

The last thing you want to happen after laying down a beautiful layer of fresh mulch is to see your house going up in flames. To avoid that, consider implementing these safety tips in your garden:

  • Place organic mulch away from the house.

  • Place wood chips, pine needles, even rubber mulch at least 18 inches from the house, grills, decks or other structures.2 It’ll decrease the chance of fire spreading to the house in case the mulch catches fire.

  • Wet your mulch.

  • Use stones, rocks or sand close to the house.

  • Organic mulch, like wood chips, pine needles, even rubber are combustible. To reduce fire risk, use nonflammable mulch like rocks and sand if you are placing it within five feet of your home.

  • Never discard cigarettes in mulch. Avoid putting out cigarettes or other burning material in potted plants, landscaping, peat moss, dried grasses, leaves or other things that could ignite easily.

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