In recent years, concerns about wildfire safety have grown among California residents, particularly in areas prone to wildland fires. Kevin Marini, a UC Master Gardener of Placer County and UC Defensible Space Educator, discussed these issues in the Spring 2024 edition of The Curious Gardener.
Marini described how his childhood memories of playing in juniper bushes around his home contrast with current knowledge about fire-prone landscaping. Juniper, once a common foundation plant, is now recognized as highly flammable and often recommended for removal near homes.
He emphasized that most homes destroyed by wildfires ignite from embers landing on vegetation or other materials close to structures. “According to Cal Fire, the majority of homes burn down in a wildland fire from embers that fly in, land in landscapes around homes or on the home itself and ignite vegetation or other materials (like outdoor furniture!). This is why there is emphasis on the Ember Ignition Zone—the 0-5 foot area around structures.” More information about defensible space can be found at https://www.readyforwildfire.org/.
Landscaping recommendations focus on three zones: the 0-5 foot Ember Ignition Zone; the 5-30 foot lean, clean and green zone; and the 30-100 foot reduced fuel zone. In each area, reducing dense plantings and organic mulches can help limit fire spread.
Marini cautioned against relying solely on so-called “Firewise” plants for protection. He explained that all plants are capable of burning under certain conditions: “First, all plants burn—there are no ‘fireproof’ plants, even though some are more resistant to catching fire and burning hot than others.” He also pointed out that maintenance practices such as regular pruning play a significant role in reducing flammability. Plants with accumulated dead material inside them can act as “ember catchers,” increasing risk regardless of species.
He referenced UC ANR Publication 8695: “A plant’s environment and maintenance generally have more influence on the combustibility of the plant than does its characterization as fire safe or not fire safe. For example, a plant with a good water supply could have a greater growth form (that is, grow taller and wider) and hold leaves longer, whereas a plant in a stressed or drought condition may have stunted growth and accumulate dead materials. Therefore, a certain species may be relatively fire resistant in one environment and less so in another.” The full publication offers further guidance at https://anrcatalog.ucanr.edu/pdf/8695.pdf.
Marini warned homeowners to be skeptical about lists labeling specific species as “fire safe.” He cited research summarized by UC ANR Publication 8695: “Be cautious about ‘fire safe’ plant lists and labels. In general, there is little evidence to support fire safe claims. In a recent review of 20 years of plant flammability studies, Bethke et al. (2016) determined that fire safe labels often relied on inconsistent types of testing or no testing at all—in part because, according to the researchers, ‘no consistent, standardized plant flammability testing or criteria for rating’ exists to assess flammability.”
The article concludes by urging homeowners to focus efforts on removing combustible materials close to their houses rather than seeking special types of plants for protection. Proper maintenance—removing dead material from plants—and breaking up continuous paths of vegetation through spacing or hardscape features remain key strategies for improving landscape resilience when faced with wildfire threats.
Additional scientific perspectives suggest that experiments assessing individual plant flammability provide limited insight into how entire landscapes respond during fires (see https://www.researchgate.net/publication/221790438_Plant_flammability_experiments_offer_limited_insight_into_vegetation-fire_dynamics_interactions).
For more detailed guidance regarding wildfire preparation measures for homeowners visit Cal Fire’s resource page at https://www.readyforwildfire.org/.