The catastrophic fires in Los Angeles County have stoked anxiety about the role of flammable vegetation around homes and other structures. Months of drought, combined with fierce Santa Ana winds, made for fires that consumed brush at rates of up to three football fields per minute.
And the long-standing injunction to clear brush and trees from around a building to create “defensible space” against fire didn’t always matter. Most of the structures lost in the Eaton and Palisades fires — 16,248, according to Cal Fire at this writing — appear to have been ignited by other buildings, not by vegetation. Stark images from the fires’ devastation have frequently shown plants and trees intact — green and unburned — surrounding the incinerated ruins of buildings.
Fires driven by strong winds are less about direct flame setting a structure alight than about missiles: firebrands — burning pieces of vegetation or structures — and especially embers — small burning particles. Firebrands in particular can be blown many miles ahead of the flaming front of a fire, starting new blazes. This “spotting” was a critical factor in the scale of damage done by the Eaton and Palisades fires. Embers, shot sideways at a building as if from a spark cannon, lodge and ignite the surface of a structure or, worse, find ways inside it, igniting it from within, no matter what it is made of.
In extreme conditions, no amount of brush clearance can guarantee protection. A moment of unwelcome clarity came in the 2017 Tubbs fire in Santa Rosa, Calif., when winds approaching hurricane strength blew sparks across the eight-lane 101 Freeway and then an arterial road, igniting a Kmart that was surrounded by an asphalt parking lot, burning it to the ground. Indeed, too much clearing can in fact leave structures vulnerable, with nothing to slow down wind-driven embers.
Given what we now know, we can — and need to — have gardens around our buildings, but gardens designed and tended with fire in mind. The most recent guidelines, including those recommended by the Los Angeles County Fire Department, specify zones of gradually increasing planting radiating out from a structure’s walls.
In the first five feet — Zone 0 — everything must must be noncombustible: concrete, stone, gravel or a similar material. Traditional foundation planting is out, as is wood mulch.
No wooden auxiliary structures should be attached to the building. Not a wooden fence and definitely not a wooden deck. This change in particular can be hard to accept for Californians who cherish indoor-outdoor living. In the Northern California town of Paradise, which was almost destroyed by 2018’s Camp fire, a proposed rule against wooden decks attached to houses, strongly supported by fire officials and scientists, was soundly rejected by remaining residents.
But there are options: first, by separating the wooden part of the deck or the fence from the structure by at least five feet of fire-resistant material — metal or cementitious boards. Decks could also be freestanding. We don’t need to lose our decks entirely, but we have to rethink them.
Zone 1, the next 25 feet out from a building’s walls, is where a garden can thrive. Paradoxically, plants rooted in deep, moist soil offer better protection here than a flat, inorganic surface. That’s because well-watered plants have high “fuel moisture,” which inhibits ignition and catches and smothers flying embers. Plantings in Zone 1 should be low, and not very flammable — more green leaves than woody stems. Succulents or lush ground covers such as star jasmine are better than rosemary, for example.
For the segment closest to your house, traditional lawn is good, but an alternative that requires less water and mowing would be even better: native sedges or yarrow, or nonnative ground covers such as kurapia. Past this first Zone 1 segment, use low shrubs — not too closely spaced, perhaps interspersed with noncombustible pathways or patios. The key is to strike a balance between the heights and massing of greenery, without creating dense thickets.
Zone 2 extends beyond 25 feet from the house, where we can have larger shrubs and carefully placed trees. In older iterations of “defensible space,” trees were anathema, but we now recognize their potential benefits. They provide shade, which goes toward another paramount goal of smart landscape design: climate resilience. And new research shows that some trees with dense, hard leaves, such as native coast live oaks, can act as a “catcher’s mitt,” stopping and knocking down flying embers before they reach a building.
Beyond 100 feet from a structure, modifying vegetation has little effect on its survival in fires. However, local fire department regulations may require “brush clearance” up to 200 feet away. Wherever your property ends in an urban environment, it is better to have perimeter walls than hedges. Working with neighbors to coordinate landscape strategies, especially where different buildings’ zones overlap, will amplify success.
Plants in the right place in the landscape are never simply “fuel.” They provide beauty, enjoyment and habitat for wild nature, and crucial protection from fire.
Wade Graham is a writer, historian and landscape designer with a practice based in Los Angeles. wadegraham.com
