Fire-resistant plants for home landscapes

Reduce wildfire risk with proper plant selection and placement

Protecting family, home and community

Fires are a natural part of the Pacific Northwest’s ever-changing ecosystem. As people continue to live and build in fire-prone landscapes, they must take steps to protect their lives, homes, properties and communities. These safeguards are needed in rural, suburban and urban environments, which are all prone to wildfire devastation.

One way to lower fire risk is to create a defensible space around your home. The Home Ignition Zone, or HIZ, is defined as the home itself and everything around it out to 100 feet (out to 200 feet on steeper slopes). Reduce potential fuel materials within the HIZ to create gaps and slow the spread of any potential wildfires toward your home.

Defensible space also allows room for firefighters to fight the fire safely. This publication uses National Fire Protection Association standards for HIZ distance (Figure 1). See more detailed information in The Home Ignition Zone: Protecting Your Property from Wildfire, EM 9247. HIZ distance guidelines may vary in individual states; check with your local fire department or state authorities on defensible space requirements.

Taking action

Most homeowners want a landscape that:

• Is aesthetically pleasing.
• Creates privacy.
• Complements their home.
• Varies in color, texture, flowers and foliage.

Plant selections should also factor in flammability, since plants contribute to potential fuel. Homeowners should reduce fuel and fire hazards around their homes and include fire-resistant plants in their landscapes. Equally important are proper plant placement, spacing and ongoing plant maintenance.

These practices, when combined, can help protect your home. They do this by blocking intense radiant heat, reducing direct contact with flames and reducing the chance that embers ignite your home (Figure 1).

Flammable plant material in your landscape can increase the fire risk directly around your home. The 2010 Oak Knoll Fire in Ashland, Oregon, is a prime example of how flammable plant material can act as fuel and contribute to wildfire. In this fire, wood shake roofs, high grass and fire-prone plants such as Leyland cypress all contributed to home loss (Figure 2).

What are fire-resistant plants?

Fire-resistant plants are those that do not readily ignite from a flame or other ignition sources. These plants can be damaged or even killed by fire. However, they tend to produce fewer embers, the most common cause for homes burning in wildfires. Their foliage and stems do not significantly contribute to fuel and fire intensity. Several other significant factors influence the fire characteristics of plants, including plant moisture content, age, total volume, dead material and chemical content.

Most healthy deciduous shrubs and trees are fire-resistant. But both native and ornamental plants can be highly flammable. Spreading or upright juniper is one highly flammable shrub often planted in home landscapes (Figure 3). Avoid landscaping with highly flammable plants directly around your home.

Most people choose plants based on flower color, light requirements (sun or shade), fragrance or overall appearance. These are all valid reasons for selecting plants. But your first priority in a fire-wise landscape should be to select the fire-resistant plants best adapted to your region. Group plants with similar adaptability, water, soil and sunlight requirements. Use drought-tolerant plants in drier locations. When choosing non-native plants, make sure they are non-invasive. Invasive plants can displace native plants, causing both environmental and economic damage.

The mature size of plants is an often overlooked factor to consider. This is especially important when planting trees or shrubs near homes. Ensure adequate spacing so that fire cannot spread into the canopy (Figure 4) or touch roof lines as the plants mature. Allow enough space for a plant to fill in without needing to severely prune it or move it as it matures. In the 5- to 30-foot zone, choose low-growing (12 inches or less) perennials or groundcovers over taller ones.

Be sure to choose plants that are adaptable to your area and suitable for your U.S. Department of Agriculture Hardiness Zone. Hardiness zones are meant to serve as guides, not as an absolute for plant selection and survivability. Many other factors contribute to whether a plant will survive and become more fire-prone. These include soil type, rainfall, heat tolerance, and exposure to wind and sun. Consider the microclimates that exist in your community and your own backyard.

Placing, spacing, mulching and maintenance

While plant selection is important, so are design and plant spacing. Avoid placing any plant material within 5 feet of the home, known as the immediate zone in the HIZ.

The intermediate zone (5–30 feet out from the home) can include fire-resistant plants that are well-maintained and adequately spaced. Allow 10 feet or more between group plantings. Increase these distances if your home is on or near slopes. Allow ample space between plantings both vertically and horizontally. Avoid planting in rows, as this can create a continuous path of fuel for fire to spread. Reduce ladder fuels (Figure 5) by removing tall grass, shrubs and small trees beneath larger trees. Keep a minimum of 15 feet between tree branches and your home.

To maintain your fire-wise landscape, follow best practices on pruning, watering, mowing heights and plant placement. For more maintenance tips, see The Home Ignition Zone: Protecting Your Property from Wildfire, EM 9247.

Using decorative mulch and hardscapes in your landscape

Mulch can help conserve moisture, minimize erosion and suppress weeds. However, it’s important to use the right type of mulch and in the right locations. Bark mulch, while a popular choice in home landscapes, IS NOT recommended within 5 feet of a home. Bark mulch or chips can easily ignite, especially when dry. Also avoid recycled rubber mulch materials, which are highly flammable. Instead, consider using nonflammable decorative rock or gravel, especially in areas adjacent to your home (Figure 6). See The Combustibility of Landscape Mulches, UN Extension SP-11-04.

Hardscaping is the use of pavers, boulders, statues, benches — anything that is not a living plant but adds design features or utility to your outdoor living space. Hardscape features that are noncombustible can add beauty and create a defensible space around the home.

Maintenance

Properly maintain your landscape in the HIZ to keep plants healthy and reduce potential fuel. Follow these practices annually as needed, particularly as the growing season progresses and plant material (fuels) accumulates or dries out.

• Keep plants, including turfgrass, well-watered to maintain plant health, sustain leaf moisture content and reduce drought stress that could lead to dead plant material.
• Remove any dead or dying plant material such as branches. Cut back spent blossoms, leaves and stems throughout the growing season.
• Prune or remove trees and shrubs as needed to reduce ladder fuels and maintain horizontal and vertical spacing between plant clusters. Prune conifers in early to midwinter to avoid attracting insect pests (Figure 7).
• Tune up your irrigation system in spring and monitor it throughout the growing season.
• Keep turf grasses mowed to 3–4 inches and native grasses to 6 inches or less.
• Remove weeds, invasive grasses and overgrown brush such as cheat grass and Himalayan blackberry.