The saying goes, “Where there’s smoke, there’s fire.” While that early proverb remains true, smoke is not the only danger during a wildfire. Embers—burning pieces of airborne wood or vegetation—can be carried by the wind for more than a mile. These embers may start spot fires or ignite homes, debris, fences and other objects.
Here we will cover ways homeowners can help reduce damage to homes and other structures by creating a fire-resistant landscape and choosing plants that are also suited to dry conditions.
What Are the Primary Threats to Homes During a Wildfire?
Research comparing homes that were destroyed with those that survived points to wind-blown embers and small flames as the primary ways homes ignite during wildfires.
Homeowners can prepare their property to resist embers and reduce the chance of flames reaching the house or attached structures. The condition of the home and the area immediately surrounding it can make an important difference. This space is known as the Home Ignition Zone, or HIZ.
The Home Ignition Zone is generally divided into three areas.
1. Immediate Zone: 0 to 5 Feet
This is the area closest to the house and the most vulnerable to ignition from embers.
- Remove leaves, pine needles and other debris from roofs, gutters, decks and along the foundation.
- Keep firewood, wooden planters, combustible decorations and wood mulch away from the siding.
- Cover exterior vents with corrosion-resistant metal mesh with openings no larger than 1/8 inch.
- Whenever possible, keep this zone free of vegetation and use gravel, rock, concrete or another noncombustible surface.
Current wildfire guidance recommends keeping the first five feet around the home as free of
combustible materials as possible. When plants are retained in this area, they should be widely spaced, carefully maintained and surrounded by noncombustible materials.
Possible low-growing plants include:
Hardy ice plant (Delosperma species): A low-growing succulent with colorful summer flowers. It works well in rock gardens but should be kept from forming a continuous mat.
Stonecrop or sedum (Sedum species): Fleshy, water-storing plants that remain low to the ground. Many varieties are well suited to hot, dry locations.
Hens and chicks (Sempervivum species): Compact succulent rosettes that can be placed among rocks or gravel.
Turkish speedwell (Veronica liwanensis): A low, mat-forming groundcover with small blue flowers.
Even these plants should be placed cautiously. No plant is completely fireproof, and accumulated dry leaves or stems can become fuel.
2. Intermediate Zone: 5 to 30 Feet
The goal in this zone is to slow the movement of fire and prevent flames from reaching the house.
- Space trees and shrubs so their branches do not touch.
- Remove lower tree limbs, generally up to 6 to 10 feet from the ground, while avoiding removal of more than one-third of the tree’s live crown.
- Keep grass mowed to no more than about 4 inches.
- Remove dead leaves, branches and flower stalks.
- Plant in small, separated groups rather than creating continuous beds of vegetation.
This zone can include low-growing perennials, lawns or lawn alternatives, and carefully selected deciduous shrubs.
Common yarrow (Achillea millefolium): A widely adapted perennial with finely divided foliage. Western native forms are available, and established plants tolerate dry conditions.
Blanket flower (Gaillardia species): A deep-rooted, drought-tolerant perennial that provides colorful flowers through much of the summer.
‘Autumn Amber’ three-leaf sumac (Rhus trilobata ‘Autumn Amber’): A low-growing selection of a western native shrub. Its spreading form can help cover soil without creating a tall wall of vegetation.
Lewis’ mock orange (Philadelphus lewisii): Idaho’s state flower, this deciduous shrub has fragrant white flowers. It should be kept pruned, separated from other shrubs and free of dead interior branches.
3. Extended Zone: 30 to 100 Feet
The extended zone is intended to interrupt the path of a wildfire and prevent flames from moving into tree crowns. On steep slopes or heavily vegetated properties, defensible-space work may need to extend beyond 100 feet.
- Thin dense stands of shrubs and trees.
- Remove ladder fuels—vegetation that allows fire to climb from grasses and shrubs into tree canopies.
- Break up large areas of brush or continuous vegetation.
- Move firewood stacks at least 30 feet from buildings.
- Remove combustible debris from around sheds, fences and other outbuildings.
Hardy native and drought-tolerant plants can be used in this zone, but they still need proper spacing and maintenance.
Arrowleaf balsamroot (Balsamorhiza sagittata): A familiar western native with a substantial taproot and good drought tolerance. Remove dry flower stalks and foliage when they begin to accumulate.
Golden currant (Ribes aureum): A drought-tolerant native shrub with yellow spring flowers and green summer foliage. It should be planted with enough space between neighboring shrubs.
Yucca (Yucca species): A low-water plant with thick leaves and a strong architectural form. Older, dry leaves should be removed because they can collect beneath the plant and become combustible.
Plant Choice Is Only Part of the Solution
A well-planned fire-resistant landscape should include healthy plants, open spaces, noncombustible surfaces and breaks between groups of vegetation. Choosing drought-tolerant plants can reduce water use, but those plants must still receive enough water to remain healthy and green.
By looking at the landscape as a series of zones, homeowners can take practical steps to reduce available fuel, slow the movement of fire and improve the chance that their homes will withstand wind-blown embers.
https://www.nfpa.org/education-and-research/wildfire/preparing-homes-for-wildfire
