Fire Safe Landscaping

A fire-safe landscape is not the same thing as a well-maintained yard. It is a landscape designed so that vegetation cannot carry fire to your home: the right plants, in the right places, with the right spacing and maintenance.

You do not need a lot of money to make your landscape fire-safe, and the result can increase property value and conserve water while improving your home's appearance. What matters most is placement and maintenance. Post-fire research consistently shows that how a plant is maintained and where it sits relative to the house has a greater effect on ignition than the species itself.

Firescaping: Design That Reduces Risk

Firescaping is landscape design that reduces your home's vulnerability to wildfire. The goal is to surround the house with things that are unlikely to burn and to break up the paths fire can travel. A firescaped yard does not need to look different from a traditional design. It still serves entertaining, play, storage, and erosion control. It simply adds fuel separation, fire-safe plant selection, and defensible space principles to the design.

• Create fuel breaks with stone walls, patios, pools, driveways, and walkways.
• Use rock, gravel, and low irrigated beds as ground cover for bare spaces and as firebreaks.
• Group plants of similar height and water needs into islands separated by hardscape or low groundcover.
• Keep trees farthest from the house, shrubs in the middle distance, and low plantings nearest the home.

Choosing Fire-Resistant Plants

There are no fireproof plants. Given enough heat and dryness, every plant burns, and a neglected "fire-resistant" plant is more dangerous than a maintained "flammable" one. That said, some species ignite less readily. Choose plants with these characteristics:

• High moisture content in leaves, which ignite and burn more slowly.
• Little or no seasonal accumulation of dead leaves, twigs, or thatch.
• Open branching and fewer total branches and leaves, which means less fuel.
• Slow growth, which requires less pruning to stay open.
• Low sap, resin, oil, or wax content. Junipers, pines, spruces, firs, and other resinous plants are highly flammable and do not belong near structures.
• Deciduous trees are generally more fire-resistant than conifers because of higher leaf moisture.

See our fire-resistant plant list for San Mateo County for native species suited to coastal and inland conditions, and our list of fire-prone plants to avoid. A nursery specializing in California natives can recommend plants for your specific site. Fire Safe Marin's fire-smart plant guidance is an excellent regional reference for the same Bay Area conditions.

Irrigation and Maintenance

Healthy, watered plants with high moisture content are harder to ignite. Drip irrigation targets water where it is needed and conserves it. Lawns and groundcovers that stay green form a low-fuel greenbelt in Zone 1. The maintenance side is just as important: remove dead plant litter as it accumulates, prune to maintain open structure, and keep plants from growing against siding, under eaves, or under decks. A drought-stressed plant of any species is fuel.

Mulch Conserves Moisture, But It Burns

Mulch is valuable for water conservation and weed control, but bark and wood mulches are receptive fuel for embers. Fine or stringy mulches (shredded bark, gorilla hair) ignite fastest, and thick mulch layers over 2 inches deep smolder and are difficult to extinguish. Keep all wood and bark mulch out of Zone 0 (the first 5 feet from any structure), and use rock, gravel, or decomposed granite there instead. Research from the University of Nevada, Reno compared common mulch products: The Combustibility of Landscape Mulches. Fire Safe Marin also maintains a practical guide to fire-resistant mulch choices.

Where Not to Plant

Keep plants out of the locations where vegetation most often carries fire to the home:

• Against siding or in the first 5 feet from any structure
• Under vents, eaves, or windows
• Under or next to decks and stairs
• Where tree limbs would overhang the roof or chimney

Plant and Tree Spacing

Spacing between grasses, shrubs, and trees is what keeps a ground fire from climbing into the canopy and moving toward your home. The spacing you need depends on plant type, plant size, and slope. Steeper slopes and larger plants require more separation.

Vertical Spacing

Remove all tree branches within 6 feet of the ground. Where shrubs grow near trees, use the three-times rule to prevent fire ladders: the clearance between the top of a shrub and the lowest tree branch should be at least three times the shrub height.

Example: a 5-foot shrub growing near a tree needs 15 feet of clearance between the top of the shrub and the lowest tree branch.

Horizontal Spacing

Horizontal spacing depends on slope and plant height. Use the chart below to determine the separation needed between shrubs and between tree crowns on your site.

Sources: CAL FIRE, Fire-Smart Landscaping; University of California ANR, Home Landscaping for Fire (Publication 8228); University of Nevada, Reno Extension, The Combustibility of Landscape Mulches; Fire Safe Marin, Create a Fire-Smart Yard.