New things are as frightening as fire. The ancient Greeks said that Prometheus stole fire from the gods. They considered it one of the four basic elements, along with air, water and earth.
Our fascination with living in the foothills of mountains, surrounded by trees, has been going on for thousands of years. But building homes on wooded hillsides and on the edges of forests—in what fire experts call the ‘wildland urban interface’ (WUI)—puts people who want to live in these beautiful areas at risk of losing their homes to wildfires.
However, things can be done to steal fire’s potential to destroy a home or business nestled in the WUI. You, their landscape contractor, can do it, by learning and applying the principles of firewise—or fire-tolerant—landscaping.
Creating defensible space
As a landscape designer for Timberline Landscaping, Inc., Bryan Darr creates outdoor environments for clients who live on the outskirts of Colorado Springs, Colorado, where many homes have forest for yards. ‘Defensible space’ is the mantra he lives by. It’s a simple concept, all about keeping flammable vegetation far enough away from a structure so that it doesn’t easily catch fire.
Darr has experienced how keeping this clear space around a property also helps the professionals who are trying to save it. “We had the Waldo Canyon fire in 2012, and the Black Forest fire in 2013. During those disasters, if firefighters couldn’t get into the space around a house, they didn’t even bother trying to save it. But the houses that had defensible spaces, created by the homeowners, allowed the firefighters room to work, to get in there and protect the structures.”
The concept of ‘defensible space’ comes from the zone theory of fire prevention. Zone 1 is the area directly around a structure, and all its attachments, such as fences and decks, for at least 30 feet on all sides. The 30-foot number is derived from the minimum distance, on flat ground, that a wooden wall can be separated from the radiant heat of a large flame before igniting. The exact required width of this zone, however, will vary, depending on local ordinances.
Zone 1 is the most critical of all. “In that zone, you want the greatest reduction of anything that’s flammable, vegetation-wise,” said Heather LaRocco, nursery projects manager at Franz Witte Landscape Contracting and Nursery in Boise, Idaho. “All debris and fire hazards, like wood piles, should be kept away from foundations,” she said. Lawns should be mowed regularly, and understories of trees pruned six to ten feet from the ground.
Zone 2 is 30 to 100 feet out from a structure. In this zone, we want to have space between trees, at least 20 feet between individual canopies, and 30 feet between clusters of two or three. Deciduous trees are preferable in this area, as they’re less flammable. Well-irrigated perennials and low-growing plants should be placed in this zone, with vertical and horizontal space between them as well.
Zone 3 is the area 100 to 200 feet out from the structure, where the property meets the wilderness. This perimeter is the first line of defense. It can be made safer by removing small conifers that are growing between taller trees, removing woody debris, and trimming the tall trees so that their canopies aren’t touching.
Picking the right plants, and removing the wrong ones, is vital to creating a fire-resistant landscape. Some plants ignite quickly, while other plants take longer to catch, and then burn slowly.
Avoid anything with a high sap, resin, oil or wax content, anywhere in the landscape; these are hot, fast burners. Notable high-resin species include juniper and eucalyptus. These trees, though lovely and fragrant, go up like torches when set afire. Juniper, in particular, has been described as a ‘gasoline plant.’ If present, they should be removed.
Coniferous fir trees contain a lot of oil, which explains why there are so many Christmas tree fires. None should be any closer to a structure than Zone 3.
Drought-resistant plants are usually good choices. These plants, which are often natives, are also fire-resistant. But Laura Camp, general manager of Tree of Life Nursery in San Juan Capistrano, California, says that many consumers don’t realize this. Slowgrowing plants that don’t require a lot of pruning are also good choices, as well as high-moisture plants that grow close to the ground, such as ice plants and aloe. Other fire-retardant shrubs include French lavender, sage and lilac.
Not so close!
Equally important as the plants you choose is how they’re placed and spaced. Dave Ryden owns Acacia Landscape Services of San Diego, Inc., in California. Though he mainly focuses on design work now, he’s got years of experience installing fire-tolerant landscapes.
“Don’t put plants or groups of plants too close together,” he advises. “Spread the material out, so there’s plenty of space between them.”
In other words, don’t make it easy for embers to jump across from one plant to the next, or for the heat of a burning plant or cluster of plants to bring its neighbors to the point of ignition.
Kathy Nolan, ASLA, president of Studio Landscape in Ojai, California, recommends placing groups of fleshy plants within Zone 2 of a house or structure, to provide a natural fire break. “Those types of plants require a bit of water, so, having them there creates a ‘moist zone’ around a building.”
If the home or business has a long driveway, make sure that plant material growing on either side won’t impede access by firetrucks. “There can’t be any plantings that’ll grow up and cause a fire hazard along that driveway,” said northern region information officer Scott McLean, of California’s Department of Forestry and Fire Protection (CAL FIRE). “We just have to have that avenue to be able to get in and out safely.”
Of course, a client will have his own preferences for certain plant materials and how he wants them arranged. You may need to help him rethink unsafe plant choices or layouts by showing him alternatives that will be equally satisfying aesthetically, and may possibly save his home someday.
For example, while it may look pretty to have low ornamentals planted directly under a tree, it creates what experts call a ‘fire ladder.’ If those plantings should ever ignite, the flames will travel upwards into the canopy of the tree.
Hardscape, mulches and turf
The non-living elements of a landscape also have a role to play in retarding the progress of wildfires. Hardscape features such as planter boxes and retaining walls, made of non-flammable materials and placed in Zones 2 and 3, can do a lot to block the path of flames and embers.
A wooden fence around a WUI-based property should probably be replaced with brick, cement or stone. “Fences are a great way for a house to catch on fire,” Ryden warns. “It travels right along the fence line, and if that connects back to the structure, that structure catches on fire, too.”
Flame also travels across the ground. Well-irrigated turf can slow it down or stop it. It’s also a good idea to install paver or gravel pathways throughout a landscape, to act as fire breaks.
Ground covers and mulches are important to look at, too, as they can either help or hinder fire. Some mulch materials are extremely flammable. Pine needles (also called pine straw) or shredded, recycled rubber should never be used as mulch in high-fire-danger areas.
Mike Freeman owns Red Valley Landscape and Construction in Oklahoma City, Oklahoma. Grass fires spread by strong winds are common in his service area, so he pays special attention to fire-resistant ground covers. “Your best bet is to use decomposed granite, or native gravel,” he said. “Placing river rocks and things like that around a property can really help resist fires.”
LaRocco remembers one landscaping job at a residence near Table Rock, Idaho. On the 4th of July, 2015, illegal fireworks touched off a wildfire there that burned about 40 acres. “You could see the fire line, literally five feet from the client’s fence,” LaRocco recalls.
“We’d lined the edge of the property with firewise plants and Perma-Bark. Everything was drought-tolerant and on a drip system.” When LaRocco looked over the property after the fire, she saw that these measures were undoubtedly what had saved the home.
The role of irrigation
Anyone living in the WUI should have an irrigation system. A University of Minnesota study looked at the aftermath of the state’s 2007 Ham Lake wildfire. In 1999, following a ‘blowdown’ that instantly created thousands of acres of downed trees and the resultant fire potential, FEMA provided grants for the installation of sprinkler systems at private residences. Ham Lake-area homeowners who took advantage of those grants had much better outcomes a few years later.
Following the Ham Lake fire, it was determined that 72 percent of the structures that had survived had working sprinkler systems. Among those structures that didn’t, only one was irrigated. The report from the study noted that, “When properly installed and maintained, sprinkler systems can be extremely effective in protecting not only the built structure but also the trees and vegetation within the sprinkler area.”
Maintenance is critical
Once a fire-tolerant landscape has been designed and installed, it isn’t the end of the story. You need to let your client know that while his yard may be fire-resistant now, it won’t be six months from now.
Plant material grows, and must be pruned and thinned periodically, or your careful spacing will be defeated. Besides, regular trimming promotes plant health. Suggest a regular maintenance contract to keep things shipshape.
In WUI areas, there are often stiff penalties for not clearing brush. In California, CAL FIRE regularly sends out inspectors to check compliance with defensiblespace ordinances.
“We look at the amount of shrubbery, and where it’s located,” said McLean. “We don’t want it against a building; that would promote fire into the structure.” Failing an inspection can bring fines, and continued noncompliance by a property owner will bring a crew out to clear the property for him, at his expense.
Fuel in the form of debris and leaves should not be allowed to accumulate under trees. Nor should the fuel that’s still attached to a tree, such as dead branches; they should be removed. Of course, some species are worse that others in this regard.
“Pay special attention to palm trees,” Ryden said. “Palms, especially Mexican fans, build up tremendous beards of dead frond thatch. If a spark flies up and hits that, the entire tree will go up like a Roman candle within minutes.”
Even if high-resin fir or pine trees are zoned correctly, away from structures, remember that they still drop lots of debris on the ground. Left in place, those pine needles are like a carpet of oily rags.
Unfortunately, there is no such thing as a totally fireproof landscape, only a fire-resistant one.
Even the best-designed, best-maintained landscape is no match for a wildfire whipped by 60-mile-anhour winds. But it’s clear that how we design and maintain a client’s property can make the difference between a mere close call and a total disaster.
While we can’t absolutely stop a raging inferno from damaging a client’s home, we can at least make things less fire-friendly, and maybe even buy enough time for firefighters to gain the upper hand over it.
In this way, just as Prometheus stole fire from the gods, we can steal fire from the landscape.