Plants can serve as wildfire fuel. Consequently, home survival during wildfire is greatly influenced by the characteristics of the plants growing adjacent to the house. The selection and maintenance of plants in the residential landscape should be an important consideration for Nevadans living in high fire hazard areas. Ideally, the area within at least 30 feet of the house should emphasize landscape plants that are difficult to ignite by burning embers and if ignited, not produce sufficient heat to ignite the house. These plants should be routinely maintained to keep them healthy, vigorous, and free of the dead material.
Unfortunately, there are no “fire-proof” plants. Any plant will burn if exposed to enough heat for a long enough period of time. There are, however, considerable differences between plants in regards to being a fire hazard. Some plants are harder to ignite, generate less heat when burning, and produce shorter flames than other plants. These differences can be attributed to both inherent characteristics (i.e., naturally occurring differences between plant species) and cultural practices (e.g., pruning, irrigation, etc.). Homeowners living in high fire hazard areas should select landscape plants with the following characteristics:
- High Moisture Content: For a plant to ignite, it must be exposed to enough heat to evaporate the water from the plant tissue. Once ignited, plants with high moisture content also burn more slowly and less intensely than those with low moisture content. Plants which possess the highest moisture content are herbaceous and succulent vegetation when they are actively growing. When they cure and dry out, however, they have a very low water content, are a fire hazard, and should be removed.
- Low-Growing Habit: Plants which are low-growing typically produce shorter flames and have less fuel than taller plants. Select shrubs that grow to a height of less than 2 feet at maturity or which can be readily maintained at this height through pruning. Use herbaceous plants that are less than 12 inches in height.
- Low Amount: Shrubs that are dense and have fine textured leaves, such as ornamental juniper, usually possess a greater amount of fuel than similar sized shrubs with a more open habit and larger leaves, such as red osier dogwood.
- Lack Flammable Chemicals: Many evergreen woody plants, such as juniper, pine, and arborvitae, contain flammable chemicals. Deciduous shrubs and trees are better choices because they usually do not contain these flammable chemicals.
Based on these characteristics, homeowners living in high fire hazard areas should select the following types of plants for use within at least 30 feet of the house:
- Emphasize herbaceous plants such as lawn, conservation grasses, some ground covers, annual and perennial flowers, and bulbs.
- Use deciduous shrubs that are less than 2 feet in height.
- Select deciduous trees.
- Do not use evergreen shrubs and trees within this area.
In terms of creating an effective defensible space, plant placement and maintenance are just as important as plant selection. For more information about good plant choices for high fire hazard areas go to www.livingwithfire.info or contact your local University of Nevada Cooperative Extension office.
Ed Smith is a natural resource specialist for University of Nevada Cooperative Extension.