by Ellie Insley, Sonoma Ecology Center Board Vice President
February, 2021
At Sonoma Ecology Center, we encourage homeowners to approach defensible landscaping from both the human perspective, and from the ecological perspective. The Sonoma Ecology Center is part of a group called the Resilient Landscapes Coalition, along with the Master Gardener Program of Sonoma County, and the Habitat Corridor Project. The goal of the Resilient Landscapes Coalition is to encourage fire-wise landscape design and management in the defensible space zone, while at the same time enhancing biodiversity and wildlife habitat, and conserving resources. For more information visit sonomaresilientlandscapes.com.
From the human point of view, we can create gardens that are fire resilient, beautiful and sustainable, with minimal maintenance and water consumption. From the ecological perspective, we can design our gardens to offer food and habitat for multiple species of wildlife, and offer other benefits including reducing erosion and sequestering carbon. These multiple goals are all possible to achieve, whether you are renovating an existing garden or starting with a clean slate.
Your house is probably the most flammable thing on your property, and hardening it is the first priority. Once your house is hardened, you can move into the garden. The first step is to consider the area closest to your home. Further hardening the area within 5’ of the home is critical to preventing flying embers from igniting vegetation adjacent to the house and potentially igniting the house. This zone around the home is a good place for walkways, or non-combustible “mulch” such as gravel or decorative rock. So if you have beloved roses, camellias or lemon trees in the 5’ zone, transplant them elsewhere, or at the very least prune them thoroughly and remove adjacent plants, so there is minimal combustible material that can ignite your home.
The next area to consider is the 5-30’ zone. Plant this area in islands of lower growing vegetation up to 3’ tall, with occasionally a larger shrub or tree, separated by non-combustible pathways and other open areas like patios. If a fire is advancing, the idea is to slow it and provide less fuel the closer it gets to the house, while leaving room for firefighters to maneuver equipment adjacent to the home. Imagine a rain of embers falling onto your property, if a fire ignites, will it be able to burn all the way to your home or are there breaks in the vegetation (pathways and patios) to limit the advance of fire?
Farther out in the 30-100’ zone, plants can be somewhat taller, still placed in islands separated by pathways of mown and well hydrated native grasses, or composted mulch or gravel to impede the spread of fire.
In all the zones, be aware of plants growing below trees, and remove any ladder fuels. The rule of thumb is that the space from the top of any plant to the lower branches of a tree should be 3 times the height of the lower plant.
A note about mulch and leaf litter, both of which are important to retain moisture, suppress weeds and provide organic matter to the soil: a 2009 study at the University of Nevada has shown that some mulches are more fire resistant than others. The recommendation is to avoid shredded mulches, such as gorilla hair, which are very flammable, and to choose mulches that have been composted for at least 2 months, or products with larger particles over 1 inch diameter. In all cases the mulch should be kept 5 feet away from any combustible structure like a house, deck or wood fence, and should be no more than 3 inches deep. Leaf litter is a natural mulch that provides essential nutrients to the root system, keeping plants healthy and fire resilient, and provides habitat to countless species of insects, spiders and earthworms, which in turn feed frogs, lizards, birds and countless other species. So a few inches of leaf litter and the right kind of mulch will be beneficial in a fire wise garden, with the right placement.
Planting in islands with a variety of species, particularly natives, will create beauty and improve biodiversity. Many of us live in Sonoma County because of the natural beauty and abundant wildlife. Unfortunately, biodiversity is declining at an alarming rate, for example – as measured by the drop in insect populations, including that of the monarch butterfly. We can do our part to turn around this drop in biodiversity by gardening to provide food and shelter for wildlife. It turns out that many of our native plant species fit the multiple objectives of providing wildlife food and shelter, while being drought tolerant and beautiful. Another benefit of gardening with native plants is that many can remain well hydrated with low amounts of irrigation.
When gardening in the defensible space zone, choice and placement of plants is important, but maintenance is equally important. Many people are misled by “fire safe plant” lists, thinking that these plants can simply be installed and forgotten, but all plants will burn if not properly maintained. Groundcovers such as California fuschia and clustered field sedge like to be sheared yearly, usually in fall, and perennials such as Cleveland sage (a CA native despite its name), need extensive pruning every 2-3 years. This occasional pruning and shearing will ensure the plant is vibrant and green, and therefore more likely to be fire resistant. For more information about native plant choices for fire resilient gardens, and their wildlife value, and maintenance needs, visit this matrix.
Another note about supporting wildlife in your garden – many birds nest on the ground or in vegetation near the ground, so be careful to leave their nests undisturbed as you prune your plants. It will help if you time any extensive removal of vegetation to avoid bird breeding season, which is between February and late August.
A word about plants to avoid: there are a number of plant species, such as pampas grass and bamboo, that are very difficult to maintain. They grow quickly, shed and collect large quantities of dead, dry material which are challenging to remove, and are not recommended in the defensible space zone. Other plants including juniper, rosemary and italian cypress tend to grow very densely, hiding dry, dead material deep within bright green outer foliage. A quick parting of the outer leaves will reveal the perfect fire brand waiting to ignite. These plants are best avoided certainly within the 0-30’ zone. This topic of fire safe and fire prone plants is quite controversial, since as mentioned before all plants will burn under the right conditions, and it’s been said that any plant if well maintained can be fire resistant. As the experts continue to debate, suffice it to say that removal of the dead and dry litter within plants in the defensible space zone is critical.
In summary, the effort you make getting to know and maintain your garden is worth it! You will ensure that your property is more fire resilient, while providing habitat for wildlife, from bees, bluebirds and robins to monarch and swallowtail butterflies.
