There are two categories of mulches: organic and inorganic. Organic mulches are usually plant materials such as pine needles, wheat straw, pine bark nuggets of various sizes, shredded western red cedar and redwood bark, wood chips from recycled pallets or wildfire fuel reduction projects and cocoa shells but also include ground and shredded rubber. Inorganic mulches are non-plant materials such as rock, gravel and brick chips.

Quarles recommends not using any organic mulch within 5 feet of a house located in wildfire prone areas. Instead, place non-combustibles such as rock, pavers, brick chips or well-irrigated, low-combustible plants such as lawn or flowers closest to the house. The more combustible mulches should be used more than 30 feet from the home.

Quarles and University of Nevada Cooperative Extension natural resource specialist Ed Smith have published a manual comparing the relative combustibility of the eight mulch treatments and their recommendations for use.

To download a free copy of ''The Combustibility of Landscape Mulches,'' visit firecenter.berkeley.edu/node/65.