Firewise Landscaping

Roofing material, plant selection, landscape design, and maintenance are the most critical elements in developing a firewise home.

Homeowners can greatly reduce the risk of wildfire by creating “defensible space” around structures. Section 4291 of the California Public Resource Code requires clearing flammable vegetation around structures a minimum of 30 feet, up to 200 feet depending on conditions. Local ordinances may be more stringent. In areas of dense vegetation, at least 100 feet of clearance is needed. However, on hillsides where fire spreads more rapidly and with greater intensity, a clearance of 200 feet or more may be advisable.

The need to be firewise must be balanced with the need for privacy, shade, and aesthetics. Reducing fuel volume and eliminating highly flammable plants in the defensible space is key to being firewise.

The Zone Concept

A practical approach to developing defensible space involves varying the level of fuel reduction, plant selection, and maintenance by zones around the structure. Typically, three to four zones are delineated. The innermost zone within 30 feet of a home is a critical buffer zone between the structure and the surrounding native vegetation.

The intent is to establish and maintain a “greenbelt” of irrigated, low-growing, fire resistant plants around the home. Some ground cover plants gradually lose their fire resistance as their lower, inner branches die. For this reason, it is advisable to prune out dead material and to mow or shear the plants periodically to encourage new succulent growth.

Additional protection can be provided by incorporating rock, brick or concrete pathways and patios, masonry walls, lawns, and rock gardens. Irrigation, dead branch pruning, removal of accumulated leaf litter and other woody debris play an integral role in the effectiveness of this zone. Bare soil in the greenbelt can be mulched with 2–3 inches of clean wood chips, fir or redwood bark with little risk. This will help reduce erosion, conserve soil moisture, retard weed growth, and improve growing conditions.

The mid zone, 30–70' from the house, is designed to provide maximum fire protection; it should contain mostly low growing, fire resistant plants. Some well-spaced, fire resistant trees can be maintained. Plants in this area should be drought tolerant; periodic irrigation will increase their fire resistance.

More native vegetation can be maintained in the outermost zone, although dense brush must be cleared and crowded trees thinned. Ideally, trees within this zone should be spaced 20–40' apart to prevent lateral fire spread. Prune off all lower branches within 10' of the ground. The removal of dead branches and trunk sprouts in the lower crown is also desirable. Space shrubs about 10–20' apart, depending on size. Small groupings can be maintained. Stagger tree placement and space irregularly to avoid alignment resulting in a continuous fuel supply.

Plant Selection

Most conifers are quite flammable, but some, like pine, incense cedar, and juniper are extremely flammable. Many species of eucalyptus and acacia are extremely flammable as well, due to their volatile oils and resins. Species with shedding bark and heavy litter drop are particularly hazardous because fire can spread more easily up the tree.

Plants considered to be highly flammable must be kept pruned-up, thinned out, free of litter and peeling, loose bark, well irrigated and at least 10 feet from any structure. Better yet, remove them.

Many native and Mediterranean plants are well suited for firewise landscaping. Base selections on slope, exposure, available space and tolerance to shade, sun, wind, and drought. The oil-to-resin content, water and mineral level and production of fine fuels (large surface area per unit volume) determine the degree of fire resistance. Local fire agencies can provide fire resistant plant recommendations and other firewise literature.

Ultimately, homeowners must accept the risks of living in the wildlands, and take appropriate measures to protect their lives, homes, property and surrounding environment from wildfire.