In wake of Sonoma County fires, here are ways to create fire-resistant gardens

There are things homeowners can do to protect their properties by planting and maintaining a landscape with less-flammable plants and trees and maintained in such a way that will reduce the chance of fire spreading.|

The recent fires have touched everyone. The physical composition and appearance of our landscapes, and our relationship with them, is forever changed. From wildlands and rural hillsides to city streets, what seemed permanent and safe can in fact be vulnerable to periodic fire. Not just the built environment, but many of our trees, shrubs and gardens are gone, living elements that act to soften and aesthetically anchor houses and buildings to the earth.

Our homes and businesses are set within and adjacent to our wild landscapes. In our leisure time, we walk, bike or drive through their majestic scenes. People travel from all over the world to enjoy the atmospheric and rugged areas that are part of appeal of Wine Country. Our intense engagement with these environments has created a strong urban-wildland interface that is susceptible to fire, a natural aspect of our dry summer landscapes.

There are things homeowners can do to protect their properties by planting and maintaining a landscape, with less-flammable plants and trees and maintained in such a way that will reduce the chance of fire spreading.

It helps to understand the larger context of fire within our built environment. California is a fire-prone landscape because of the state's long dry season, low relative humidity, occasional high heat and winds and frequently abundant vegetation that provides fuel to fire. Ecosystems and their communities have developed and evolved in this environment. Periodic fires are a natural aspect of most California ecosystems. Some are fire-dependent and require fire for seeds to germinate, renew overgrown vegetation, open forests to sunlight and provide nutrients for certain plants. The soft, new growth of native shrubs that grow after a fire provide food for deer and other wildlife. Bare soil and the lack of competition from shrubs and trees allow annual wildflowers to grow. Too frequent fires destroy seedbanks, and young trees and shrubs before they are old enough to set seed, which leads the landscape to convert to grasslands.

Flammable plants

Dry conditions, low relative humidity and winds help create physical conditions conducive to fire. Dry vegetation and structures like houses feed fires. The golden hills that are an ubiquitous feature of California's identity, are composed of more than 90 percent non-native grasses and forbs, generally found as broad-leafed flowering plants.

We have both purposely and inadvertently converted our natural understory landscape of perennial grasses and annual wildflowers to very flammable non-native grasses. These plants grow quickly with the advent of winter rains, set seed and die early in the spring. They are highly flammable (often called “flashy), and allow fires to spread rapidly. They are dangerous when they invade or are adjacent to shrub or chaparral plant communities, as the grasses act as ladders into the flammable shrub overstory. These grasses also dry much earlier in the season than other vegetation, extending the seasonal fire danger.

Chaparral, the most common plant community in the state, is composed of densely growing shrubs such as manzanita, chamise and Ceanothus that form a closed stand over time. It is a fire-dependent ecosystem, yet fires historically occur there only about once or twice a century. They are often severe, eliminating most standing vegetation. Many shrubs and trees of this ecosystem either sprout from the base, or their seeds are stimulated to grow by fire and the resulting bare soil. Fires rejuvenate these areas. In conifer forests, fires were more frequent, and usually patchy, and lighter in intensity, mostly consuming the understory and young trees with branches that reach the ground.

With the advent of effective fire suppression, forests are widely considered more dense and even-aged than they were naturally. As a result, fires are now often severe and enter and spread in tree crowns. In oak woodlands, trees and shrubs both grow singly and in clumps. Older hardwood trees such as oaks, madrone and California bay often have no lower branches as a result of age. They are usually set in wide expanses of dry grasses that are highly flammable. Winds can act to move flame from ground level into tree canopies.

Over 90 percent of fires are started by human activity. Mowing, power lines and sparks from cars, cigarettes and campfires cause fires far more frequently than do lightning strikes. As happened with the recent Wine Country firestorms, winds have a great influence in the generation and severity of fires and the catastrophic speed at which they move, and can cause devastation in areas never considered at risk.

Make landscapes safer

Choosing appropriate plants for a fire-prone landscape, strategically siting and pruning plants, minimizing dry fuels such as grass, and adequately watering plants can have an effect on how landscapes behave in the event of a fire. Larger landscapes need to have defensible space around structures. Defensible space is defined as space where the vegetation has been designed or modified and maintained to reduce flammability, and where firefighters can defend a structure.

Urban and rural areas have different laws and concerns about their properties and gardens. In rural areas existing fire ordinances govern how landscapes are managed. Most break down areas of concern into defensible space zones corresponding to distance from houses or structures. In an urban or suburban setting, where houses are closely spaced, and lot sizes are small, houses themselves form the majority of combustible fuels. In these spaces, we can still lessen the chance that our gardens will contribute to spreading fire to other homes. Minimizing the use of highly flammable trees such as Monterey pines, junipers and eucalyptus, irrigating our plants well, keeping trees, vines, shrubs and ground covers free of dead leaves and stems and thinning dense vegetation, will all make your landscape less vulnerable to fire destruction.

Create defensible space

Zone 1: 1-30 feet from structure.

Remove dead plants and dead grass/weeds.

Remove any overhanging tree branches over roof.

Trees should have a 10-foot space between them.

Use low nonflammable shrubs under windows and around decks.

Zone 2: 30-100 feet from structure.

Mow dead grass to 4 inches.

Keep fallen leaves/needles/small branches and plant debris at no more than 3 inches deep

Eliminate ladder fuels to trees by limbing up trees to 6 feet from the ground.

Create horizontal space between trees and shrubs. Space trees and shrubs widely. (See CalFire website for details).

Create vertical space in between trees and shrubs. Remove shrubs under trees that could act as ladder fuels. (See CalFire website for details).

Fire-resistant plants

All plants can burn.

Irrigate plants adequately. Well-watered plants require more energy to ignite and sustain combustion.

Maintain plants free of deadwood/twigs/stems.

Thin dense tree and shrub canopies to reduce fuels.

Limb up trees 6-10 feet from ground level to minimize “fire ladder” effect. Limb up shrubs so foliage does not touch ground.

In wildlands thin chaparral shrubs. Base-sprouting plants like coyote brush, chamise and coffeeberry can be cut down every few years in fall to reduce fuel load and keep vegetation young.

Chose fire-resistant plants for your garden. Fire-resistant plants are open in growth habit, don't accumulate dead wood/leaves/stems, and are free of flammable resins/oils and turpenes.

Use more low-growing plants (less than 2 feet tall) than upright shrubs or trees.

Space plants adequately for each fire zone and around structures. On large lots and properties, the immediate critical 30-foot area around houses should have only widely spaced, well-irrigated specimen trees and low plantings free of mulch. Sprinkle compost around plants for soil fertility. From 30-100 feet from houses, space trees 20-40 feet apart. Space shrubs widely. Low plantings should not be contiguous.

Thin or remove highly flammable plants, such as many conifers, especially near structures. Deciduous trees are less flammable.

Have adequate numbers of plants with deep and extensive roots (such as native plants), to hold and protect soil during winter rains, especially on slopes.

Use mulches with low flammability. Mulches that have large air spaces between particles or pieces are more flammable. Shredded barks can be highly combustible. A 2-inch layer of woodchips, and even better, composted woodchips or composted greenwaste have low flammability and tend to smolder rather than flame. Compost has less flammability still, as particles are very small and closer in composition to that of soil. Consider installing microsprinklers in mulched areas so mulch can be moistened during times of red-flag fire warnings. Red-flag warnings are when humidity is less than 19 percent and winds over 25 mph. Intersperse mulch with non-combustible materials such as pavers, decomposed granite, gravel or rock.

Mow annual grasses and weeds in a 100-foot perimeter around structures to 3 inches in height before they are completely dry to minimize any fire spread and fire ladder effect.

You can reach columnist Kate Frey at On Twitter @katebfrey. Or visit her at

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