What to plant (and not plant) to be safer from wildfire in Sonoma County

Our homes and businesses are set within and adjacent to wild landscapes in Sonoma County. In our leisure time, we walk, bike or drive through their majestic scenes. People travel from all over the world to enjoy the bucolic and rugged appeal of the Wine Country.

Yet our intense engagement with these environments has created a wide urban-wildland interface that is susceptible to catastrophic fire, an altogether more destructive and deadly force than the periodic fires that are a natural aspect of most California ecosystems.

Homeowners can help protect their properties by planting landscapes with less flammable plants and trees and maintaining them in such a way that will reduce the chance of fire spreading. Here is some background and tips to follow to do your part to help reduce fire risk.

Fire history, behavior

The golden hills that are an ubiquitous feature of California's identity are mostly composed of non-native grasses and forbs. We have both purposely and inadvertently converted our natural understory of perennial grasses and annual wildflowers to very flammable nonnative grasses. These plants grow quickly with 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 scrub oak, 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.

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.

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 or thinning 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.

Below are some ideas of plants to use in your garden. Combine widely spaced trees and shrubs with noncontiguous low-growing plants that share the same needs. Pick six to 12 plants out of each category list depending on whether you prefer a simple plant palette or a varied one, and group each variety or repeat them throughout the garden.

For an all drought-tolerant garden, consider using Chinese pistachio or California buckeye as specimen trees. For shrubs, choose California redbud, Serviceberry (Amelanchier), or crape myrtle, widely spaced. They are long-lived, deep rooted, floriferous, and wildlife friendly.