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Taming the Flames: Make Your Landscape More Fire-resistant

By Kerry B. Badertscher, Colorado State University Cooperative Extension agent, horticulture

Whether you live in the mountains or plains, low snowpack this past winter may affect the safety of your home and family this summer and fall. Current snow pack levels for the Front Range are about 50 percent of normal, and this translates to a potentially dangerous fire season. So what can homeowners do to decrease fire hazard?

Recommendations include creating a defensible space, modifying the landscape design and choosing appropriate plants.

Creating a defensible space in the landscape is a way of allowing room for firefighters to access property safely. A defensible space is defined as that area between a home and the oncoming wildfire that has been modified to reduce the potential threat of destruction.

To modify a landscape, use the three R's of defensible landscapes: removal, reduction and appropriate replacement of foundation plants, including trees, shrubs, grasses and perennials. One method is to plant in small, irregular clusters rather than large masses. Another method is to space plants farther apart. These techniques have been shown to reduce the fire's intensity.

Modify the overall landscape by creating a ring of paths or concentric circles of paths. Use inorganic mulches such as pea gravel or stepping stones as opposed to organic mulches that fuel fires. Both of these methods slow the speed of fire moving from one area to another.

Types of Plants to Use

Native plants are considered the most appropriate, but remember that a native at 10,000 feet is not native at 6,000 feet. Some plants, such as ones with thick, succulent leaves or ones that shed leaves in extreme drought, have been demonstrated to reduce fire hazard. There also appears to be a correlation showing that plants that adapt to high salty soils may be resistant to burning.

Grass mixes may be native or non-native and should be tailored to the site, such as an exposed sunny site or a northerly site with more moisture. An all-purpose native grass seed mix may include 20 percent of each of the following: Arizona fescue, Western wheatgrass, streambank wheatgrass, Indian ricegrass and blue grama. Keep grasses mowed 3 inches or lower when they are close to structures such as the house, garage, decks, firewood piles, fuel tacks, shrubs and trees. Grasses should never exceed 8 inches in height elsewhere on the property. Mowing grasses in the fall and again prior to spring greenup will reduce the fuel.

Wildflowers may be used in creating a defensible landscape. However, left unchecked, the plants may be a large source of fuel at the end of the season. Try using them in contained areas with appropriate walkways and isolated from structures to lend a naturalized setting to your landscape.

Other flowers and ground covers that will perform at up to 9,000 feet elevation, have known drought tolerance and are recommended for fire-safe vegetation include thick, succulent foliage plants in the sedum family (stonecrops). Rudbeckias, sea thrifts, veronica and low-growing plants such as creeping phlox may also be used. Plants that are indigenous to your elevation and locale will most likely perform the best.

Shrubs are a major concern to firefighters because they can act as a fuel ladder for the fire as it moves from the ground up into the tree canopy or up into a house. Some shrubs, such as conifers, may have resins and are considered more flammable. Deciduous (ones that drop their leaves in the fall) shrubs are considered less flammable because they have higher water content. Leaf litter should be gathered each fall and spring, and all shrubs should be placed away from any structures. Keep grasses mowed around shrubs to keep the fuel down. Removing suckers or sprouts from the base of a plant will further reduce the hazard. Some shrubs that have done well in firewise landscapes include Oregon grape holly, Western sand cherry, golden currant and even native wild roses. These plants need extra moisture via supplemental irrigation to become established. Remember, even these recommended shrubs, if used in the wrong place in the landscape, can become a fire hazard.

Plant Native Trees

Trees are, of course, a significant source of fuel in a wild fire. It's best to use trees that are native to your elevation and habitat. Do not plant trees near structures, and do not allow them to grow and touch buildings. Ideally, trees should be spaced about 20 to 25 feet apart and at least 15 feet from any structure, especially a chimney, power lines and roof areas. Thinning may be necessary to allow the mature growth at proper spacing intervals. Prune branches up 10 feet from the base on mature trees. Younger trees should not be overpruned. Avoid using trees that have a full crown or ones with branches that persist, such as blue spruce. Some trees that may be used include the Rocky Mountain maple, thinleaf alder, serviceberry and riverbirch. Whatever you choose for a landscape plan, sometimes less is more when it comes to fire safety.

Check with your local fire district for more information. If the local fire department is rural and dependent on volunteers, response time to a fire may be slower. Either way, lend them a hand by properly thinning trees and brush within the defensible space. Remove trash and other debris from the property. Avoid having any plant material come in contact with the chimney or roof, and use a chimney screen to avoid unwanted sparks. Stack firewood at least 15 feet uphill of the home. All structures on the property should be included in the defensible zone.

Check with your local fire department for more home safety tips. For more information, see Colorado State University Cooperative Extension Fact Sheets:

Creating Wildfire-defensible Zones
Fire-resistant Landscaping
Forest Home Fire Safety
Firewise Plant Materials
Grass Seed Mixes to Reduce Wildfire Hazard

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010