In this new era of climate change and megafires, how can we work with our environment to protect homes, lives, and livelihoods? We can start at home, with native plants. Much of the information in this article is adapted from the Sustainable Defensible Space project and the “Using Native Plants for Fire-Resistant Landscapes” webinar by landscape contractor Greg Rubin, founder and president of California’s Own Native Landscape Design. Greg Rubin presented this webinar in late 2020 as part of our CNPS East Bay Chapter’s monthly speaker series. We recommend you watch it in full!
No matter where your home is, it may be at risk from wildfires. Embers can travel long distances from fires up on ridgelines down into more urban areas, which means it’s important to safeguard your home even if you’re in a city. “Hardening” your home and garden against the threat of wildfire requires taking into account how fire behaves in order to create a landscape that is more fire resilient—that is, less likely to ignite and more likely to recover after burning—and in turn less likely to ignite your home or those nearby.
Home landscaping also has a direct effect on how our wildlands are treated. Some fire professionals are beginning to talk about how home and landscape hardening relates to large-scale vegetation management being planned and carried out in the state’s wildlands. Zeke Lunder, pyrogeographer and founder of wildfire safety company Deer Creek Resources, told KQED’s Forum that “home hardening and community protection is really important, not just to save the people’s homes, but so we can let fires burn in the back country. There’s all these places that we need to have fire… If we have communities that are defensible from fire—where fire can burn around the community and not burn up the community—we could actually let fire burn on the landscape. I think as long as we deny fire’s place on the landscape, we’ll never get ahead of it.”
The U.S. Forest Service defines defensible space as an “area either natural or manmade where material capable of causing a fire to spread has been treated, cleared, reduced, or changed to act as a barrier between an advancing wildland fire and the loss to life, property, or resources.” Here are three tips for creating defensible space around your home.
Use lightly irrigated native plants
Native plants, like any vegetation or organic matter, are flammable. No plant is completely fire resistant. However, dry fuels ignite and burn faster and are more likely to ignite surrounding fuels. Think of starting a fire at camp or in a woodstove: you need dry, brittle material (kindling) to get the denser logs to catch fire. If you try to use damp wood to get a fire going, it’s much harder.
It’s the same for a plant whose tissues have been fully hydrated from rainfall or supplemental irrigation. Windborne embers may consume themselves before they can sustain sufficient heat to dry out a plant with high moisture content. Most native plants require less water to stay hydrated than non-natives, as they’re adapted to California’s climate pattern of little to no rain from late spring through fall. A study of fuel treatments in the wildland-urban interface (WUI) conducted in May of 2020 by Jon Keeley, Greg Rubin, and colleagues showed that “lightly irrigated native shrubs planted around homes can reduce fire hazard while possessing other desirable features of utilizing native vegetation.” Rubin noted in his webinar that drought-tolerant non-native plants need about twice the amount of water as natives to achieve a level of fire-resistant hydration.
Rubin lightly irrigates coastal scrub gardens in San Diego with about three quarters of an inch of supplemental water monthly during the summer. He prefers overhead watering with micro-sprinklers (which better simulates rainfall conditions) rather than watering with drip irrigation.
Create defensible space with zonal design principles
Some homeowners completely clear all ground-level vegetation as a fire prevention measure. However, having lightly-irrigated and thinned native plantings on the property may disturb the flow of the ground surface winds that carry wildfire embers and may catch and cool some embers. Rubin’s friend and colleague Rick Halsey, director and founder of the California Chaparral Institute, paints a vivid image when he says some completely cleared properties can create a “bowling alley for embers.”
Healthy plant communities also store carbon and transpire moisture from the soil as they photosynthesize, releasing moisture into the atmosphere as part of the water cycle. Rather than completely clearing a landscape of plants, focus on strategic thinning of vegetation on your property and careful management. Removing 40-50 percent of vegetation using the zonal design principles below can actually reduce the fuel volume by much more, perhaps around 70 percent, depending on the site. The zonal design principles are most applicable to larger properties—for smaller urban lots with close neighbors, focusing on zones 0-1 and home hardening will be most relevant.
Zone 0: within 5 feet of your home. This is the area where you should try to completely remove combustible material to create an ember-resistant zone. This includes plants, furniture, building materials, etc. Tall plants directly under the eaves of the house can carry fire up into the eaves and roof, and even low-growing plants under eaves can generate embers that threaten the house.
Zone 1: within 5-30 feet of your home (or 50 feet if there’s a slope). In this zone, Greg Rubin recommends low-growing, well-spaced, lightly-irrigated native plants with hardscaping and fire-resistant or inorganic mulches. He has successfully used this design strategy in residential landscapes in wildfire-prone areas.
Zone 2: within 30-100 feet of your home (50-100 feet if there’s a slope). In this area, it’s critical to remove weeds—and that includes non-native weedy annual grasses, which act as flashy (readily ignited and rapidly consumed) fuels that can ignite other plants, including natives. Dense vegetation plus oxygen provides the ideal setting for fires to intensify and spread. If you have trees, it’s recommended that you leave a good amount of space (at least three times the height of the understory) between the lowest tree limbs and the vegetation below it. Limbing up trees and/or pruning the understory is a common fire resilience practice at the start of the fire season to help prevent flames licking up from the underbrush from setting the canopy on fire.
Work with your local conditions, not against them
Increased fire resilience begins by designing or modifying the landscape and planting layout, starting with the first five feet from the walls of the house. There’s no set plant list that is best for every site in California—the most resilient plants are going to be those adapted to your specific climate and soils. You can use the Calscape Garden Planner to find suitable plants for your region and conditions.
Although there aren’t specific guidelines for exactly which plants to use, Greg Rubin suggests a ratio of about 75 percent evergreen to 25 percent perennial native plants as a recommended mix for fire resilience. The wildland-urban interface study mentioned earlier found that the evergreen native shrubs tested in the study exhibited the highest moisture content. Keep your perennials easy to access so you can deadhead spent flowers and remove dried out foliage throughout the season.
If you have a larger property, add paths and features around your shrubs and trees. These small breaks make the garden easier to access and enjoy and also prevent dense clumps of vegetation that create more risk in a wildfire situation.
An East Bay example
Laurel Martin-Harris lives in the Berkeley Hills in the Codornices Creek watershed. She has been actively working on making her hillside property more fire resilient by managing and removing large stands of invasive hemlock, Scotch broom, ivy, and thistle. She’s working to restore the property to a wooded, shady coast live oak (Quercus agrifolia) and bay laurel (Umbellularia californica) habitat in order to set the stage for a healthy native plant community to thrive.
When Martin-Harris moved in, the property was overgrown with non-native grasses, ivy, and thistle, forming a dense underbrush that dried out in the summer and fall and left fine, dry fuels.
Martin-Harris has worked to remove non-natives, particularly focusing on “ladder fuels” such as ivy, which was climbing up the tree trunks. She noted that beneath the verdant top layer, the ivy was dry and brown and posed a risk of carrying flames up into the canopy of the tree if it ignited.
“Ladder fuels are one of the biggest issues because people don’t realize that ivy burns…even just removing the ladder fuels in the right season makes a huge difference. Ivy does a lot of hillside holding work, but what we need are native grasses and shrubs that will do more consistent stability work,” says Martin-Harris.
“We thinned this lot for the first time in 30 years. I thought the neighbors were going to be upset, but everyone was really happy and excited about what we were doing,” Martin-Harris told us. “It’s not about clear-cutting everything—it’s thinking about what you can replace it with. This is more than just a trimming job, this is a restoration job.”
Share your fire-resilient garden
Have you been home hardening with natives? Share your fire-resilient garden photos and tips with the CNPS East Bay community. Email us your examples at email@example.com and we’ll share the best ones on Instagram and Facebook!
You can view all of Greg Rubin’s tips in the recording of his “Using Native Plants for Fire-Resistant Landscapes” webinar for our CNPS chapter. In his presentation, you can see case studies of residential landscapes he designed using the principles outlined in this article. Some of those landscapes were tested by wildfires multiple times.
Sustainable Defensible Space: Eco-appropriate homescaping for wildfire resilience.
Protecting the Wildland-Urban Interface in California: Greenbelts vs Thinning for Wildfire Threats to Homes. Jon E. Keeley, Greg Rubin, Teressa Brennan, and Bernadette Piffard. Bulletin, Southern California Academy of Sciences 119(1), 35-47, 25 May 2020.
Calscape Garden Planner: Find native plants suited to your garden.
— Jane Francis, with original illustrations by Stephanie McKenna; both are Conservation Committee members, CNPS East Bay Chapter