Firewise Landscaping

By Dr. Scott Sherman
From the August 2024 Issue

Wildfires have burned, and continue to burn, significant areas of the western States and North America. In these areas, landscapers can directly improve or inadvertently worsen the fire safety of client properties. From maintenance gardeners to contractors, arborists, and landscape architects, our work directly affects garden flammability and how readily a nearby fire will spread to and ignite buildings. This is now a major issue of survivability and insurability of properties.

Do you know how to create “defensible spaces” around homes?  How do wind/slopes affect the movement of fire in a landscape? Are certain mulches less flammable? How can we design/maintain gardens to interrupt and slow fire movement? What are resilient landscapes? How does climate change increase urgency to answer these questions? Though clients may not ask, we can initiate discussions and become strong trusted partners, protecting their properties and safety.

Removing and cutting down built up vegetation to reduce fire fuel and prevent fire laddering. (Photo: Dr. Scott Sherman)

Don’t Fuel The Fire

Climate change affects vegetation (“fire fuel”) in landscapes everywhere. We’re experiencing earlier and higher temperatures in Spring, fluctuating rains year to year, and higher winds/enhanced growth of flammable weeds and grasses that often dry out earlier in the Spring and Summer. This increase in wildfire potential is not just in the Wildland-Urban Interface (WUI), which is a great-risk zone where unoccupied or undeveloped wildland meets human development. It happens in yards of homes, HOA, apartment buildings, and landscaped commercial properties.

This is an opportunity for landscapers to create landscapes that resist, withstand, recover, and are resilient to fires. In fact, I have helped two large HOAs ultimately achieve formal Firewise USA® Community recognition, a program administered by National Fire Protection Association (NFPA) and co-sponsored by the USDA Forest Service and the National Association of State Foresters.

Working with the support of local fire department experts and inspectors, we can prioritize and guide our clients to:

Eliminate the most flammable tree and plant species;
Rake up dead leaves, whip weeds, and flammable grasses early;
Clear leaves and fuels under decks and move flammable sheds and materials 30′ or more away from buildings;
Develop effective ‘defensible space zones’ around buildings;
Create fuel breaks between existing/new plantings to mitigate fire movement horizontally and vertically within landscapes; and
Ensure easy access to the perimeters of buildings by Fire Department personnel.

Key Elements Of Firewise Landscapes

Whether for an HOA, single-family residence, or landscaped commercial property, the same elements define a firewise landscape. It takes specific knowledge, time, and sufficient resources to create and maintain firewise landscapes.

Defensible Space. Create a buffer zone between buildings and potential wildfires to slow down or stop the spread of flames and to provide firefighters with a safer area to operate. Clear vegetation and other flammable materials within zero to 5′ from the walls of a building or structure with no plants and the surface is either hardscape or otherwise kept free of any flammable materials such as vegetation and firewood, including under decks (Zone 0).

Firebreaks & Fuel Breaks. Design landscape features to act as barriers to slow or stop the spread of wildfires. This can include pathways, spaces between planting beds, hardscaping on grade, walls, and turf areas that interrupt the continuity of fire fuel.

Fire-Resistant Building Materials. With the support of fire prevention experts, guide property owners to use fire-resistant materials in construction/renovation of buildings. Examples are fireproof roofing and siding, small-opening vent screens for walls and roof soffits, and gravel and hardscaping in Zone 0.

Fire-Resistant Plants. Use less-flammable plants to significantly reduce risk. These plants have high moisture content, low oil content, and resist burning. They slow the movement of fire in a landscape. Though geared to California, Fire Safe Marin (FireSafeMarin.org) provides examples of over 150 common plants and trees. These include certain species of succulents; hardwood trees such as ash, redbud, and maple; shrubs like boxwood, blueberry, and azalea; and ground covers such as creeping thyme, wild ginger, and stonecrop to name a few.

Similarly, remove highly flammable plants such as arborvitae, junipers, cypress, cedars, and more. While any plant can burn if dead, poorly maintained, or drought stressed, Fire Safe Marin says fire-prone plants include one of more of the following:

Often blade-leaf or needle-leaf evergreens, or grasses.
Often have stiff, woody, small or fine, lacey leaves.
Leaves & wood containing volatile waxes, fats, terpenes or oils.
Sap is usually gummy, resinous, and may have a strong odor.
Usually contain plentiful fine, twiggy, dry, or dead materials.
May have hair covered leaves.
May have loose or papery bark.
Usually flame (not smolder) when ignited with a match.

See a list of California species in the sidebar at right.

Irrigation. Sufficient watering keeps vegetation green and more resistant to fire. Balance fire resistance with water conservation.

Native Plants. Native plants provide food and shelter to native wildlife. Some native plants are adapted to fire and regenerate after fires. They regrow from seeds, roots, stumps, and trunks after a fire.

Non-Combustible Materials. Don’t rely on fire retardants or irrigating mulch when a fire approaches as the benefits are short lived. Some mulches ignite and spread fire. Use fire-resistant mulch to minimize the spread and eliminate fuel sources. Since embers often accumulate adjacent to structures, keep this area free of ignitable materials.

Within 5′ of structures, use non-combustible, inorganic gravel, rock, decomposed granite, pavers, flagstones, or concrete for paths and patios and keep the area free of leaves and other organic materials that accumulate in this area. From 5′ to 30′ of structures, composted wood chips may be used in limited areas. Composted wood mulches, shown in scientific testing (see FireSafeMarin.org) to burn at the lowest speed and shortest flame length, may be difficult to source locally. Avoid large, continuous areas of organic mulches. Near structures, avoid shredded redwood or cedar (sometimes called “gorilla hair”) as it is highly flammable. Use ornamental gravels and boulders as mulch to beautify planting areas. It is better to use organic mulches selectively and not within 30′ of structures and combustible landscape items such as furniture and wooden fences.

Plant Spacing: Design, create, and maintain horizontal and vertical spacing between plants and trees to prevent fire moving from one area to another. The slope of a landscape area also affects plant spacing.

When designing or thinning out plants and trees to mitigate horizontal movement of fire, consider the anticipated mature size of plants and trees. For a flat to mild slope (<20%), space plants 2x the height of the plants and trees 10′ between the edges of the mature canopies; for mild to moderate slopes (20%-40%) space plants 4x the height 20′ between the edges of the mature canopies; for moderate to steep slopes (>40%) space plants 6x the height 30′ between the edges of mature canopies. Similarly, create larger spacing between groups of plants so if one ignites, the fire is less likely to spread to adjacent areas.

To mitigate vertical movement (laddering) from vegetation into a tree, prune off low limbs a minimum of 6′ from the ground and as high as 10′ (do not prune more than 1/3 of the height of the tree to maintain health.) If shrubs grow under a tree, create a minimum clearance of 3x the height up to the lowest limb. On slopes, prune trees higher and maintain greater spacing between trees.

Regular Maintenance: Regularly remove dead vegetation, leaves, and other flammable debris. Prune trees and shrubs to mitigate horizontal and vertical movement, mow weeds and wild grasses early, and keep roofs and gutters clear.

A weed whipped area with regrowing and flowering shrubs separated from limbed up trees. (Photo: Dr. Scott Sherman)

Achieving FireWise USA Site Designation

As mentioned, our company helped two large HOAs plan and improve their landscapes and achieve formal Firewise USA Community recognition. The process is not complex. Firewise USA (FW-USA) provides useful templates with prompts to help complete a plan and application. Their process is to Organize It, Plan It, Do It, and Tell FW-USA about it. Then, they provide support for What Happens Next. It’s key to have strong support from HOA leadership and your local Fire Department fire-prevention representative(s).

Early in 2018, for an ~300-acre condominium HOA at a WUI, the HOA Landscape Chairperson and I conferred on site with the local fire-prevention Fire Marshall to identify and prioritize firewise landscaping projects. We completed a Community Wildfire Action Plan summarizing actions and objectives for the next several years. We also met with the HOA Board to educate and receive funding for planned activities.

At the end of 2018, after substantial Firewise site work, our team submitted the Firewise USA® Recognition Program Community Assessment Template. This was a more detailed plan with summaries of work done, supported by numerous “before and after” photos, and showing where additional work was planned. Similar steps were followed when I helped a larger HOA comprised of single-family homes achieve Firewise USA recognition.

The template included:

An introduction describing the who assisted with data-gathering;
Definitions of the Home Ignition Zones (also called Defensible Space Zones.)
A description of the community’s homes and proximity to landscaping, fuels, weather, and wind conditions year-round. It also included “laddering” risks.
A geographical and topographical site description.
Results of the site assessment and plan covering annual vegetation and tree care, pruning, removal of flammable fuels.
Important considerations such as clear identification of more flammable trees and other plants, tree limbs near buildings and roofs, and other “ladder” fuels.
Observations and recommendations: structural and aesthetic tree pruning and tree/dense shrub removals; collaboration with the City and Fire Department expert on fire prevention and mitigation.
Successful firewise modifications made and planned to ‘harden’ buildings to meet WUI fire codes for roofs, gutters, vents, siding, windows, sliding glass doors, and exterior doors. “Hardening” involves finding ways to prevent ignition of the surface of a structure, such as blocking pathways for embers to enter through vents or  other openings. Other modifications included removal of sitewide, highly flammable junipers.
Next Steps included setting up a Firewise Board, completing hazard assessment and action plans, establishing an annual budget per household, creating a plan to host a FW-USA Community Education event annually, and communicating ongoing reminders to residents on ways to help keep the home ignition zones under control—such as not leaving flammable materials near the outside of buildings during wildfire season (e.g., door mats, furniture, stacked firewood.)

To ensure a FW-USA site maintains its firewise landscape conditions, the FW-USA reviewers verify steps taken and asks you to create an updated 3-year plan. This plan includes:

Education and Outreach Goals;
Home Hardening Goals;
Defensible Space/Fuel Reduction Goals; and
Evacuation Planning (Ex. Preparedness & Routing) and Wildfire Preparedness.

Before removal of highly-flammable junipers and pruning to increase defensible space around a residence. (Photo: Dr. Scott Sherman)

Creating & Maintaining Firewise Landscapes

In my work on these projects, I have found certain principles apply. Here are my recommendations for creating and maintaining firewise landscapes:

Aim for timely, prioritized and continuous improvement at sites of all sizes.
Clearly understand the firewise practices required by clients’ insurance companies.
Continuously teach crews, arborists, and other professionals how to successfully plan, design, and maintain firewise sites.
Develop trust with clients and residents so you can work effectively together to prioritize and improve landscaping.
Ensure a good working relationship and regular communications with clients, residents, decision makers, HOA Boards, and fire department fire-prevention experts so that adequate funds are allocated to address top priority landscape improvements required.
Help clients to prioritize site work to remove, prune, and separate plantings including trees.
Help ensure sufficient funds are allocated to maintain the firewise landscape. Sometimes, fire departments and government agencies can provide funding along with professional guidance.
Take a practical and science-based approach to protect structures, common areas, and landscaping of each property.
Work closely with local and regional fire department experts whose job is to guide, support and communicate current codes to ensure you develop firewise landscapes.
Work with landscape architects and designers who understand how to design and specify plantings and materials that are firewise, beautiful and resilient.
Work with landscape crews and arborists who understand why and how to do initial and subsequent work to create and continuously maintain firewise sites.

Each of us can make a difference. Achieving Firewise USA recognition is just one actionable plan. Creating a safer, more fire-resistant landscape requires ongoing maintenance, client and community education, communications, planning, and investment in new landscape design and maintenance approaches.

For more information:

Dr. Sherman is the owner of AvidGreen Landscaping in Greenbrae, CA, and an ISA Certified Arborist in Marin County. As Landscape Chairman for the Greenbrae Property Owners Association for over three decades, he manages the common area landscaping of this suburban community of approximately 450 acres. Sherman has an MS in Horticulture and Viticulture from the University of California, Davis, and a PhD in Instructional Systems from Florida State University. 

Do you have a comment? Share your thoughts in the Comments section below, or send an e-mail to the Editor at jessica@groupc.com.