The Real Dirt on Wood Mulch Flammability: Lessons from the Almeda Fire

Firefighters noted something important during the 2020 Almeda Fire. They were constantly putting out fires in bark mulch around homes only to come back and find the same mulch burning again. Homes and businesses commonly had mulch pushed up to the foundation line and when mulch burned it all too easily lit the building on fire. Also, wood mulch was catching fire and throwing sparks and embers onto neighboring properties, spreading fire and igniting buildings.
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Though there have been studies of bark mulch in the past, they didn’t use mulches commonly found in the Rogue Valley. So, Ashland Fire & Rescue and Stephen Gagne (former chair of the Ashland Wildfire Safety Commission) designed a study of local mulch flammability. Jackson County Fire District #3, in White City, hosted tests during peak August heat last year to best simulate summer wildfire conditions, as pictured above.

“We found that basically all samples of mulch that had obvious wood in them were flammable and some were so flammable they really shouldn’t be used at all. That makes perfect sense given what we saw during the Almeda Fire,” said Chris Chambers, Wildfire Division Chief at Ashland Fire & Rescue.

“Yet, we still see people spreading flammable wood mulches adjacent to homes and generally overused in landscapes given how high of a fire risk our town faces,” Chambers added.

The results of the study showed that larger chunk wood mulches burned rapidly and intensely. Fine-grained mulches and bark dust burned with less intensity, but still with enough heat to catch an adjacent building on fire. Compost mulch, or mulch with very little to no discernible wood pieces, did not catch fire or let it spread. Of 13 samples tested, only one mulch, a compost, didn’t spread fire. Another compost tested later more informally also didn’t spread flames or smolder.

“Our climate is changing and we have to adapt our ways of living if we want our community to thrive in the coming years. Landscaping is one thing we can adapt to more fire and less water with comparatively little effort,” said Division Chief Chambers.

The webpage and video emphasize safe and attractive alternatives to flammable wood mulch, including rock mulch, hardscaping, and even bare dirt as options.