By Iris Craig, UC Master Gardener
Many residents of Napa Valley are continuing to recover from the October wildfires. These horrific fires killed people and animals, devastated homes and gardens and left the ridges above our valley scarred and bare. Thanks are due to the first responders for all that survived. My neighbors, friends and I are just beginning to imagine a different, healed and beautiful landscape with new and repaired homes.
I find myself wondering why some homes survived and others did not. Outbuildings, garages and studios burned to the ground, but some of the nearby houses themselves survived.
How did some landscapes remain untouched or minimally damaged? A friend told me that her house was untouched by the flames, but her front yard burned to the concrete porch where the fire stopped.
Why is this possible? How can we prevent this tragedy from happening again? What do research and personal experience tell us about designing our future landscape?
A wildfire requires a source of ignition. Once ignited, it needs fuel to spread. The gusting winds in early October contributed to the rapid spread of three fires in our area. Despite the wind and the moving flames, some areas survived. Why?
We can look for answers in the dynamics of wildfire: the need for fuel to feed the fire; and the tendency of fire to move upward. You can see this in the burn areas along our ridges and at the top of the hills. This is why flames ladder up trees and burn in the canopy. With good landscape choices, we can thwart the rapid movement and intensity of fire.
The aim of fire-wise landscape design is to create a defensible space. Assess your site. What are the elevations? Is your home near the top of a hill or a cliff? Do your home and outbuildings border a heavily wooded area? Or are they in an urban area, close to other homes, with trees?
Many of us thought we would not be touched by the fire because we lived in the city. However, the devastation of a Santa Rosa neighborhood demonstrated that we are not safe. We all need to think about fire-wise landscaping.
Determine how much defensible space you need for your home. California law now requires that homes have 100 feet (or to the edge of the property) clear of forest debris with tree crowns spaced 100 feet apart. If you live on a hilltop or ridge, you need an additional 50 feet on the downside of your property, with a recommended six feet between plants.
Next to lack of defensible space, flying embers are the greatest threat to homes and surrounding vegetation. For this reason, any heavy equipment used in fire-vulnerable areas is required to have spark arresters for fire prevention.
Cal Fire (the Department of Forestry and Fire Protection) recommends keeping the 30 feet nearest your home as a “lean, clean and green zone.” No trees or bushes should touch the buildings. Any plants or trees in this space should be those identified as less likely to burn quickly.
Many of us have created water-wise landscapes, eliminating grass, installing drip systems and topping the ground with various types of mulch. Some mulches can ignite quickly from embers.
The University of Arizona Extension studied the flammability of mulches. The least flammable were stone and aggregated granite. Researchers ignited several types of ground cover including straw, wood chips, shredded bark, garden mulch and bare ground. Hay ignited quickly. Bare ground, garden mulch and shredded bark proved less likely to ignite and are considered appropriate for a fire-wise landscape. Hardscapes, including walkways and retaining walls, also tend to thwart a low-burning fire.
Tall grasses; bushes planted in a row; chunks of bark; wooden fences; piles of firewood or debris; or a butane tank with tall grass beneath it are all vulnerable to ignition by embers. Clustered, low-fire bushes; grasses; shredded bark and native plants under four inches tall reduce the fire risk.
California fire code requires keeping the next 70 feet around the home as a reduced fuel zone, with all logs and stumps removed. It's okay to preserve one standing dead tree per acre to support wildlife. If it should fall, it must not touch buildings or roadways. Keep plants under trees small and watered as needed. Prune trees to create a six-foot vertical gap between trees and shrubs to discourage the laddering of fire.
With science-based information, we can begin to create a fire-wise landscape. We move forward, step by step, to recreate our gardens and homes and protect ourselves, as much as we can, from the ravages of fire.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.