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Steaming Piles of... Mulch

By By Vickie Frantz, Staff Writer
May 09, 2012, 4:14:54 AM EDT

Mulch used in spring landscaping projects can be hot enough to produce steam or even ignite a fire.

Mulch is made of wood and as the wood begins to decompose it produces heat. When mulch becomes too dry, the heat can build until a fire begins from spontaneous combustion. Dark mulch can heat more rapidly than lighter colored mulches.

"Mulch catches on fire because the sun dries it out," said John McCartney. McCartney is a professional landscaper for Landscape II, Boalsburg, Pa.

Windy and hot weather increases the risk of a mulch fire. The heat and wind can dry out the mulch making it more susceptible to burning. Landscaping lights that are placed in a planter should be placed far enough above the mulch to prevent heating. Mulch that is spread too thick also increases the fire risk, according to

The fire risk can be controlled by keeping the mulch moist. Periodically check the mulch by looking for areas that are steaming or producing gray ash. Steam rising off a pile of mulch occurs when the hot air from the decomposing wood mixes with cooler air. If you find an area that is steaming, soak it thoroughly with water.

Spread the mulch in thin layers. Dispose of cigarettes and other smoking debris in proper containers. Never throw them into mulch.

When placing mulch in planters close to buildings, leave space between the mulch and the building. If a mulch fire occurs, the space can keep the fire from damaging the building.

Protect your home and property by taking these precautions if you use mulch in your landscaping projects.

This video of steam rising off of a pile of mulch is courtesy of Youtube user WinWinSituations.

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