December 27, 2013
Incorporating fire-safe concepts into your residential landscape is one of the most important ways you can help your home survive a wildfire.
A house burns because of its interrelationship with everything in its immediate surroundings — called home ignition zones. To avoid a home catching on fire, homeowners must eliminate the wildfire's potential relationship with their house by eliminating the amount of flammable vegetation and materials surrounding the home, and increasing the moisture content of remaining vegetation.
Changing a fire's path by clearing a home ignition zone is an easier task this time of year, when plant growth is slower and trees are dormant, and one that can prevent the loss of a home when fire season arrives.
Creating defensible zones does not mean you have to have bare earth around your home. With proper planning and modification, you can have a beautiful landscape and a fire-safe home. In general, trees should be kept farthest from your home, shrubs can be closer and well-watered high-moisture content bedding plants and non-flammable landscape materials like rock, stone or cement may be nearest. Dead and dying plants should always be eliminated from your landscape through regular maintenance.
A fire-safe landscape consists of two zones: the home-defense zone and the reduced-fuel zone. The home-defense zone encircles a home for at least 30 feet on all sides, much greater if your home is on a steep slope or in a windswept exposure. Within the home-defense zone, plants should be well maintained, well spaced, well pruned, and free of resins, oils or waxes that burn easily. All flammable vegetation and other combustible materials should be removed within 30 feet of the house.
The reduced-fuel zone is from 30 to 100 feet or greater depending upon slope and wind conditions. In this zone, plants should be low growing, well-irrigated and less flammable. Clusters of two to three trees should have 30 feet between them. Plant mixes should contain both deciduous and coniferous trees. Create fuel breaks with hardscaping using gravel walkways, stone paths and lawns that interrupt potential fuel continuity.
Spacing and vegetation arrangement is key in fuel management. Most fires start as surface fires, and spread on the ground from plant to plant and then to your home. Spacing plants, particularly on slopes, so plants don't touch will reduce the chance of fire spreading to your home from low-lying plants bunched together and then laddering a wild fire up to your structure. Make certain there is horizontal and vertical separation in your plants and trees. Trees should be limbed up between 6 to 10 feet from the ground and smaller trees by a third and kept 10 feet from your roof. It is important to reduce the chance that flames would reach the crown of your tree where heat intensity and flame length is increased.
Other areas of consideration are eliminating flammable fabrics used in outdoor cushions and upholstery on deck seating areas near the house, and removing other flammable materials and firewood, propane tanks and plastics that can ignite from underneath overhangs and under decks. Even plastic plant pots should not be stored under a wooden deck; they can ignite with embers that are sucked into the air trap of a deck during a wildfire. Use 1/8-inch wire mesh behind any lattice underneath decks to help prevent embers from a wild fire from being sucked into those areas and igniting your home's wooden structures.
Mill Valley's fire department has prepared a fire-prone plant list and recommends eliminating or not planting high-oil content plants such as bamboo, pampas grass, fountain grasses, rosemary, junipers, French and Spanish broom, cypress species, eucalyptus, Australian tea trees, and most pine and fir trees. Lawns should be mowed regularly and grasses kept low. A fire-free area should be created within the last 5 feet of your house with nonflammable landscape materials like stone, pavers and rock and high-moisture content annuals and perennials. Water the plants and trees in your home-defense zone regularly and mulch to retain their moisture. Avoid hairy or gorilla mulches that could ignite easily in your both your home defense and reduced fuel zones.
Maintain your irrigation system regularly. Store firewood stacks more than 30 feet from your house. Groupings of succulents and drought-resistant potted plants help keep moisture content high near your home's structure.
For more information on how to help your home survive a wildfire by fire-wise landscape practices, check firewise.org or anrcatalog.ucdavis.edu and use the link for lawn and garden to order brochures on fire safety in your landscape. Firefree.org offers a list of fire-resistant plants to consider for planting to increase your protection from wildfires.