Defensible Space for Wildfires

Wildfires are a real and present threat throughout the West, especially in Southern California and San Diego County. Many homes and businesses sit adjacent to steep canyons or rural landscapes choked with brush that can easily ignite from lightning, carelessness, or arson. This threat requires that all homes and businesses included defensible space in their landscape design to reduce the risk of fire damage and sometimes to even qualify for insurance coverage.

California's history with fire

Prior to European conquest of California, the indigenous tribes living here used fire as a tool to keep meadows, creek beds, and forests clear of brush buildup. Should a wildfire or accidental fire occur, there was rarely enough fuel to create high-heat fires or devastating crown fires. These intentional burns also helped select for species that provided them with cordage, food, weaving materials, medicines, and forage for wildlife, as well as helped reduce disease and insect infestations in plant communities.

As we've colonized California and displaced its tribal peoples, we've lost an important tool in the ecological management of our landscapes. US forest managers mandated wildfire suppression for all wildfires which led to massive buildups of fuel, which, when ignited, could reach into the upper canopies of trees causing extensive damage.

Fire and modern living

If you live in a rural zone, or next to a green/brown belt corridor, it's important to review your landscape's defensible space for wildfires.  How they are designed and maintained can mean the difference between saving or losing your home.

Home protected from wildfire by following defensible space suggestions (photo © San Diego County)

The 2003 Cedar Creek wildfire spurred legislators and fire officials to push for stricter rules requiring cleared space for firefighters to help combat any blazes and reduce the risk of structural fires and property loss. Now, the County of San Diego requires 100 feet of defensible space for homes in unincorporated rural settings. Native habitat such as chaparral and scrub has evolved with fire and poses a great risk to those living in the countryside.

As we saw in the Carlsbad fire of 2014, homes are still vulnerable even if they're within incorporated city areas, but with proper landscape planting, hydrating, and routine maintenance, you can mitigate your home's fire risk.

What is defensible space?

Defensible Space is the area around a structure where combustible vegetation that can spread fire has been cleared, reduced or replaced. This space acts as a barrier between a structure and an advancing fire. County of San Diego Owners living in unincorporated San Diego County are required by law to create two barriers around the home and other structures. The first ring is a 50' distance of irrigated and/or fire resistant plants, well spaced along with irrigated plants. The second 50' ring is to be kept clear of any plants taller than six inches above ground.

Cal Fire adds additional safety tips regarding this and other similar laws in California with their"reduced fuel zone" flyer.

Irrigated plants won't catch fire easily*, and plants that lack flammable resins and oils like eucalyptus will have a lower chance of spontaneously erupting in flames from excessive radiant heat or falling embers. If they do catch, they'll also burn at lower temperatures and not as long as highly resinous trees and shrubs.

(*That being said, even ice plant and other succulents will burn given the right conditions, and depending on the topography, a house with 50' of cleared defensible space can still catch fire if winds and flame heights exceed 40' in length.)

Designing ecologically with and defensible space in mind

Traditionally, brush fires repeatedly swept through our canyons, valleys, and gorges racing up hillsides clearing dry, dense underbrush. After passing, the scared and denuded landscape left room and new niches for life to spring forth again. Unfortunately, life, homes, and property don't spring forth after such renewing energies making it imperative that we design our landscapes thoughtfully and effectively.

Dry landscapes catch fire sooner than saturated landscapes

Water does not like to catch fire. Sometimes it happens, but survivors of many fires can lend some of their luck to their irrigated landscapes. In a locations like San Diego where up to 80% of our water is imported and we're in a State of Emergency due to drought conditions, we can't water our landscapes like we live in Florida, but we can reuse water we've already used.

Greywater irrigation is beginning to catch on across America

Other countries already have mandates for the efficient collection, distribution, or reuse of rainwater and greywater, the water you previously used for showers, laundry, sinks, and possibly the kitchen. Black water (or toilet water) is too contaminated with biological toxins for safe and sanitary use for conventional landscapes.

By keeping used water out of septic lines and using it in our landscapes, we can create hydrated zones that will nourish soils and plants, and provide shade and protection to our structures. Irrigation systems are still required for plants used in such systems for the times when residents are traveling, but the demand on city or well water is reduced.

There is already a no-permit option for household laundry-to-landscape greywater installs in San Diego County. Check with your municipality to see what greywater systems are allowed, and if your homeowner insurance will cover an install.

Capture and infiltrate water where it falls

When it does rain in Southern California, we ought to be doing everything within our potential to slow, spread, and store rainwater in our most widely available and cheapest location: the ground.

Landscapes that effectively build up organic matter in the soils are more capable of infiltrating and storing excess rainwater. Proper ecological landscape design will integrate earthworks and other water catchment and infiltration strategies to help reduce dependency on irrigation and lead to healthier plants and trees.

Effectively designing and installing rainwater catchment systems on your home, hardscape, and landscape will ensure that the little rain we do get stays for as long as possible in the areas you need it to.

Plant appropriate species within your defensible zones

Properly choosing your plant palette can improve your home's survivability in a fire.

Evergreen, non-resinous trees are ideal for your upper canopy, but should be located a good distance away from your home to avoid spreading any fire to your structure. If you want tree shade to cool your home, plant a tall growing, well irrigated species like ash or fruitless mulberry.

Succulents are an excellent alternative to non-native foliage that and help reduce water consumption. If shrubs are wanted around the home, plant low lying, non-resinous shrubs.

Routine Maintenance and Clearing is Essential

Landscape with gravel and stones around structures and set plants a safe distance from the house.

Always clean out leaf litter from gutters. Remove broken tree branches touching the ground and avoid dense plantings where shrubbery can create fire ladders and climb into the upper story canopy.

Is your landscape defensible?

Please take this time to review your fire danger sectors for your home and community. Also take the time, if you haven't already, to discuss your evacuation plan with all of your family members. A dry run of what you'd grab in an emergency, where your exit routes are, and who to contact will make a stressful event safer and easier to handle.

We hope those fighting fires in our neighborhoods and communities stay safe, and that everyone take the time to reach out to and comfort neighbors and friends who suffer unimaginable losses.

More information on defensible space in San Diego County

• County of San Diego Defensible Space and Fire Safety Page
• List of Plants Best Suited for Defensible Space in San Diego County
• San Diego Brush Fire Pamphlet