Landscaping in the defensible space zone
By Ellie Insley
At the Sonoma Ecology Center, we encourage homeowners to approach defensible landscaping from both the human perspective and 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 like 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 to the garden. The first step is to consider the area closest to your home. Further hardening the area within five feet 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 five-foot 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 five-to-thirty-foot zone. Plant this area in islands of lower growing vegetation up to three feet tall, with an occasional 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 30–100foot 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 three 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 two months, or products with larger particles over 1 inch in diameter. In all cases, the mulch should be kept five feet away from any combustible structure like a house, deck, or wood fence, and should be no more than three 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 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 alarmingly, as measured by the drop in insect populations, including that of the monarch butterfly. We can do our part to reverse this drop in biodiversity by gar- Defensible – from page 13
dening 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 wellhydrated 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 fuchsia and clustered field sedge like to be sheared yearly, usually in fall, and perennials such as Cleveland sage (a California native despite its name), need extensive pruning every two to three 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, their wildlife value and maintenance needs, please visit https://docs.google.com/spreadsheets/d/ 1MJLJiG7AhJGvrsVCpQ-LPXKhPYa_I2DN/ edit#gid=362118465.
Another note about supporting wildlife in your garden: There are many birds’ nests 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 that 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 firebrand waiting to ignite. These plants are best avoided certainly within the zero-to-thirty-foot zone. The 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 wellmaintained, 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.
This article first appeared in the Fire Safe Sonoma Newsletter.