Does bark mulch near the house raise fire risk?

What the Carson City test found

The University of Nevada Cooperative Extension publication The Combustibility of Landscape Mulches reports an evaluation run in Carson City in 2008 by the Carson City Fire Department, the Nevada Tahoe Conservation District and two Extension offices. Eight mulches were lit on a hot, dry afternoon with fans simulating wind, and flame height, rate of spread and temperature were measured.

Shredded rubber, pine needles and shredded western red cedar showed the most hazardous fire behavior. Composted wood chips showed the least hazardous behavior overall.

Distances to remember

Because every mulch tested was combustible, the publication does not recommend any of them within 5 feet of a house or other structure. It suggests rock or other noncombustible material there. The Living With Fire guide agrees: Zone 0 should hold no wood mulch.

From 5 to 30 feet the Living With Fire guide allows mulch in a limited way. It says to limit wood mulch to 1 inch in depth and to make distinct islands surrounded by green, irrigated plants or hardscape, so the mulch cannot carry fire to the house. The publication puts the most hazardous mulches at more than 30 feet from the house, if used at all.

Mulch is not the villain

The same publication lists real benefits: less water use, cooler soil, fewer weeds and less erosion. Mulch also helps trees, and a small ring around a trunk away from the house is a different matter from a bed against the wall.

We chip wood and brush, and wood chips are on our service list, but we would not spread them against your siding. For where chips do and do not belong, read free wood chips: uses and limits. The arborist can check your beds at an estimate visit; call 775.232.8243.