Six steps to creating an effective defensible space:
The term “defensible space” refers to the area between a house and an oncoming wildfire where the vegetation has been managed to reduce the wildfire threat and allow firefighters to safely defend the house.
Make your house safe for firefighters to defend.
Having firefighters present improves the odds of a house surviving a wildfire. For safety reasons, firefighters are more likely to protect homes that have defensible space.
In the event that firefighters are not available, defensible space also improves the likelihood of a home surviving without assistance.
An effective defensible space can save your home.
Unfortunately, when some homeowners hear the term “defensible space,” they envision a large expanse of bare ground surrounding their home. While this is certainly effective at increasing home survivability, it is unacceptable for aesthetic reasons and can contribute to soil erosion. It is also unnecessary.
Fire smart landscapes can also be attractive.
A homeowner can have both an effective defensible space and an attractive landscape.
The following six steps describe how to create an effective defensible space.
Step 1: Determine the size of an effective defensible space.
The recommended defensible space zone distance is measured from the base of the house, extending outward.
The first step is to determine the size of an effective defensible space. The size of the defensible space zone is usually expressed as a distance extending outward from the house in all directions.
The recommended distance is not the same for every home. It varies depending on the type of vegetation present and the steepness of slope surrounding the home. Use the “Defensible Space Zone Calculator” to determine the right distance for you.
Once the recommended distance for defensible space is known, mark it by tying strips of cloth or flagging to shrubs. This becomes the “defensible space zone.”
If the defensible space zone exceeds your property boundaries, seek permission from the adjacent land owner before doing work on their property. It is important to note that the effectiveness of the defensible space zone improves when entire neighborhoods implement defensible space practices.
The next five steps apply to the vegetation growing within this area.
Step 2: Remove dead vegetation.
Is there any dead vegetation within the defensible space zone? If so, remove it.
Dead vegetation includes…
dead and dying trees
dead native and ornamental shrubs
dead branches
dead leaves, needles, and twigs that are still attached to plants, draped on live plants, or lying on the ground within 30 feet of the house
dried grass, weeds, and flowers
Remove all dead trees from within the defensible space area.
Remove all dead ornamental shrubs, especially juniper.
Once wildflowers dry out and turn brown, remove them.
Step 3: Create a separation between shrubs and trees.
Within the defensible space zone, check if native trees and shrubs, such as Jeffrey pine, pinyon, juniper, and sagebrush, are widely spaced or occur in a dense stand. Dense stands of trees and shrubs pose a significant wildfire threat. If this situation is present within the defensible space zone, thin dense tree and shrub stands.
On flat ground, provide a separation of at least 10 feet between Jeffrey pine and white fir.
Jeffrey Pine and White Fir: On flat to gently sloping terrain, Jeffrey pine and white fir should be thinned to provide an average separation between canopies of at least 10 feet. For homes located on steeper slopes, the separation distance should be greater. When selecting trees for removal, consider cutting unhealthy, damaged, or weak trees.
Thinning dense stands of Jeffrey pine helps reduce the threat of crown fire.
Pinyon and Juniper Trees: On flat to gently sloping terrain, pinyon and juniper should be separated from one another by at least twice the height of the average tree. For homes located on steeper slopes, the separation distance should be greater.
For example, if a pinyon tree height is 12 feet, there should be a separation between tree branches of at least 24 feet. This separation is usually created through removal of other pinyon and juniper trees.
Dense stands are a significant fire hazard.
Dense stands of shrubs also pose a significant wildfire threat. If this situation is present within the defensible space zone, thin dense shrubs stands. On flat to gently sloping terrain, individual shrubs or small clumps of shrubs should also be separated from one another by at least twice the height of the average shrub. For homes located on steeper slopes, the separation distance should be greater.
For example, if the typical shrub height is 2 feet, then there should be a separation between shrub branches of at least 4 feet. Remove shrubs or prune to reduce their height and/or diameter. In most instances, removing big sagebrush is the preferred approach. It is a very flammable plant, is easily removed, does not resprout, and is typically abundant
Unhealthy trees should be a priority for removal.
Dense stands of trees are vulnerable to insects and disease.
Step 4: Create a separation between tree branches and lower growing plants.
If trees are present within the defensible space area, there should be a separation between the lower growing vegetation and the lowest tree branches.
A burning juniper ignited the lower branches of this pine.
Vegetation often occurs at different heights or layers, like the rungs in a ladder. For example, dried grass may be the lowest rung, shrubs are the next highest rung, and tree branches are the upper rung. Vegetation that can carry a fire burning in low growing plants to taller plants is called “ladder fuel.”
Vegetation that can carry fire from ground level into the tree branches is called “ladder fuel.”
By removing some of the rungs of the ladder, the amount of wildfire fuel can be greatly reduced. The recommended separation for ladder fuels is three times the height of the lower vegetation layer. For example, if the lower vegetation layer is 2 feet tall, then there should be a separation of 6 feet. Prune the lower tree branches, shorten the height of shrubs, or remove lower plants. Do not, however, remove more than one-third of the total tree branches. This could be detrimental to tree health. As an alternative, remove the lower vegetation layers.
A tree before and after ladder fuel removal.
When there is no understory vegetation present, remove lower tree branches to a height of at least 2 feet above ground. This will help prevent burning needles and twigs lying on the ground from igniting the tree.
Step 5: Create a Lean, Clean, and Green Area extending for at least 30 feet from the house.
The goals of the Lean, Clean, and Green Area are twofold: First, the area eliminates easily ignitable fuels, or “kindling,” near the house. In the event that flying embers begin landing in your yard, they would be unable to start a fire. Second, the area keeps fire intensity low if a fire does ignite near the house. Should a fire start within 30 feet of the house, the fuels present would be unable to generate enough heat for a long enough time to ignite the home.
For most homeowners, the Lean, Clean, and Green Area is also the residential landscape. This area often has irrigation available, is planted with ornamental vegetation, and is regularly maintained.
Consider these fire-smart tips for creating a Lean, Clean, and Green Area within 30 feet of your home…
Within the Lean, Clean, and Green Area, remove most or all flammable wildland plants. These would include: pinyon, juniper, mountain mahogany, big sagebrush, bitterbrush, rabbitbrush, and cheatgrass. If you wish to retain a few of these as specimen plants, make sure they are free of dead wood and leaves, pruned to reduce the amount of fuel, and separated from wildland vegetation.
Retaining native wildflowers, such as lupine, phlox, and balsamroot, is acceptable. The top growth should be removed once it dries out and turns brown. Desert peach and Mormon tea can also be retained within this area as long as they are kept free of dead wood, are less than 3 feet in height, and are separated properly.
Good wildland plants for the Lean, Clean, Green Area.
Select less flammable landscape plants. Unfortunately, there is no such thing as a fireproof plant. Any plant can burn if it is exposed to enough heat for a long enough period of time. The good news is that there are some plants that do not ignite as easily nor burn as hot as other plants. Some rules of thumb in selecting landscape plants for the Lean, Clean, and Green Area are…
Healthy, well maintained flowers are good choices for the Defensible Space Zone.
Shorter is better than taller. All other things being equal, shorter plants are a better choice than taller plants. Taller plants can produce longer flames and contain more fuel than lower growing plants. Emphasize the use of plants that are less than 2 feet tall at maturity.
Herbaceous is better than woody. When green and healthy, herbaceous plants such as flowers, succulents, and lawn, are better choices than woody plants, such as shrubs and trees. Healthy herbaceous plants have a much higher water content than woody plants. The higher the plant’s water content, the harder it is to ignite and the more slowly it burns. When herbaceous plants dry out, however, they ignite easily, are a fire hazard, and should be removed.
Short varieties of deciduous shrubs, like barberry and spirea, are good choices for the Lean, Clean, and Green Area.
Deciduous is better than evergreen. Many evergreen shrubs and trees contain flammable oils and resins that burn very hot when ignited. For this reason, deciduous shrubs and trees are usually a better choice for landscape use in the defensible space.
Bad plant choices. Ornamental juniper and arborvitae can burn very hot. Also, their dead leaves often accumulate in and under them and are extremely flammable. They are easily ignited by flying embers. Ornamental pines, such as Scotch pine, Austrian black pine, and mugo pine, are poor choices for use in the defensible space. Scotch broom has been identified as a particularly flammable plant, as are most large ornamental grasses when they become dry. Both are considered poor choices.
Flammable wildland plants that should be removed from the Lean, Clean, and Green Area.
A well maintained lawn is a good choice for the Lean, Clean, and Green Area.
Good plant choices. Good choices for the Lean, Clean, and Green Area include deciduous shrubs, such as barberry and spirea. A green lawn is low growing and has a high water content, so is an excellent Lean, Clean, and Green Area plant choice. Lawn, however, does have its drawbacks such as having relatively high water and maintenance requirements. Clover and conservation grasses, such as crested wheatgrass, may be suitable alternatives, especially if irrigated and mown occasionally. Flowers, including perennials, annuals, succulents, and bulbs, are good choices as long as they are actively growing. Once they start to dry out and turn yellow, dead leaves and flowers should be removed. Ground covers are excellent choices for the Lean, Clean, and Green Area. Well-maintained deciduous trees are also good choices. Plant deciduous trees so that there is at least a 10-foot separation between branch tips at maturity.
Emphasize hard surfaces and mulches. Emphasize the use of hard surfaces and mulches within the Lean, Clean, and Green Area. Hard surfaces include materials such as concrete, asphalt, and brick. Mulches can be rock, wood, or bark. Rock mulches are a great choice. Wood and bark mulches may be flammable and should be kept at least 3 feet away from combustible house and deck materials. Wood mulches can burn, but they typically smolder and produce little, if any, flame. Ideally, keep them moist with irrigation during fire season.
Clear flammable vegetation away from propane tanks.
Propane tank. The propane tank is often located in the Lean, Clean, and Green Area. All flammable vegetation should be cleared from within 10 feet of the propane tank and other fuel tanks if present. Screening the propane and other fuel tanks with fire-resistant materials can provide additional protection.
Remove problem tree limbs. This includes tree limbs within 10 feet of the chimney, limbs touching the house or deck, limbs overhanging the roof, and limbs encroaching on power lines.
Create a Noncombustible Area. The area within 3 feet of your home needs to have a very low potential for ignition from flying embers. During an intense wildfire, embers may pile up next to the house. If wood mulches are present, they may add fuel to the embers and eventually produce enough heat to ignite the house. Emphasize the use of irrigated herbaceous plants, such as lawn, ground covers, and flowers, and rock mulches and hard surfaces within 3 feet of your home. This recommendation is particularly important for wood-sided houses.
Dried cheatgrass is extremely flammable and should be removed from the Defensible Space Zone.
Create a separation between shrubs that is twice the average shrub height. For example, if the typical shrub height is 2 feet, remove shrubs to create a separation of 4 feet.
Remove low tree branches or prune understory shrubs to create a vertical separation of three times the shrub height. For example, if the shrub height is 3 feet, remove low tree branches to a height of 9 feet above the shrub.
