Fire Safe Gardening

One or two minutes may be all the warning you get when it comes to fire.


In light of all the fires raging in Northern California, I am dedicating today’s post to fire safety and how it pertains to the plants around your home.


Several years of drought have killed hundreds of millions mature trees across the country. In California, over 102 million trees have died since 2010, and 62 million trees died in 2016 alone! Many of the remaining trees are not as healthy as they could be, due to bark beetle infestation and disease. These trees have more dead leaves and dry twigs, making them susceptible to fire.

Raging wildfire (National Weather Service, NOAA)

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Fire in landscapes

You learned it back in elementary school: fire needs fuel, heat and oxygen to keep going. A single spark can land on dry grass, move to a shrub, climb a tree, and then leap to your home, taking everything you own with it. It can also take your life. Gardening for fire safety means interrupting that spread. Rather than allowing fire to move through your landscape using shrubs and trees as a super highway, you can create spaces that slow or stop the flames.


California state law (Public Resources Code 4291) requires that all rural homes have a 100-foot defensible space. Suburban homes face different challenges, but fire safety is still critical and many of the suggestions still apply. Each county has its own set of ordinances, so be sure to check with local authorities. Even without the law, fire safety around your home just makes good sense.


Defensible space

Defensible space can slow or stop the spread of fire. It also helps keep you, your family, and our heroic firefighters safe. Your defensible space is made up of two zones.


Zone 1 - According to CalFire, the first zone consists of a 30-foot perimeter around any buildings, sheds, or decks on your property. Maintaining this zone means:

• remove all dead vegetation
• remove dry leaves and pine needles from the roof and rain gutters
• prune tree branches to keep them 10 feet away from your home and each other
• move patio furniture and other flammables away from trees and shrubs
• move woodpiles and other flammable materials into Zone 2

Zone 2 - The second zone extends 100 feet from your home. To maintain Zone 2:

• keep grasses mowed to 4 inches or less
• rake up fallen leaves, needles, and twigs
• create horizontal space between shrubs and trees
• create vertical space between trees, shrubs, and grass

Spacing plants and trees

By creating space between trees and shrubs, the spread of fire can be slowed or stopped. The spaces are both vertical (up and down) and horizontal (side to side). To maintain safe vertical space, remove any tree branches that are 6 feet from the ground or less. In areas prone to wildfire, bushes growing near tree canopies need three times their height before the lowest tree branches to prevent fire from spreading. This means that a 4 foot tall shrub would need 12 feet before the closest tree’s lowest branch to be fire safe.


Horizontal spacing is a function of slope. Areas that are flat or with slopes less than 20% can allow trees to be 10 feet apart. Shrubs should be two times their height apart. This means 4-foot shrubs should be 8 feet apart to be safe. Slopes of 20 to 40% require shrubs to be 4 times their height apart and trees need 20 foot spacing. To keep slopes greater than 40% fire safe, trees should be 30 feet apart and shrubs need to be 6 times their height apart. These rules apply to rural properties, but you can apply them to your suburban home, as well.


What about all that mulch?

Nearly everything you read in The Daily Garden reminds you of the benefits provided by mulch: moisture retention, weed reduction, temperature stability, reduced soil compaction, and so on. But what about flammability? Does all that ground cover create a path for fire? Luckily for us, a group of fire and gardening professionals got together in Nevada to test various types of mulch. This is what they learned about each type, listed in order of worst to safest, all used at a depth of 2- to 3-inches, unless stated otherwise:

• shredded rubber - burned the hottest (630°F), flamed the highest (over 3 feet)
• pine needles - second fastest rate of spread
• shredded western red cedar - “Gorilla hair”; fire spread the fastest, at nearly 50 feet per minute, at 380°F, with one foot flames and many embers
• medium pine bark nuggets - moderate flames, with a low spread rate
• Tahoe chips - moderate flames and spread [Tahoe chips consist of wood chips, pine needles, and other plant biomass from tree chipping operations - this is probably the closest to what you will acquire from a tree trimmer in your area.]
• Tahoe chips with fire retardant - the retardant only slowed the spread of fire by 5 to 10 minutes
• Tahoe chips, single layer - lowest temperatures, low spread, and low flame height
• composted wood chips - the only material that did not “demonstrate active flaming combustion”, with only “incidental flaming with smoldering”; spread at a rate of less than 0.3 feet per minute [the chips used were composted by a proprietary process]

Use fire-resistant plants

We all know that green plants burn a lot more slowly than dead, dry plants. And there are no truly fire-resistant plants. If it gets hot enough, anything can burn. You can help keep your home safe by planting low-growing, high-moisture plants closest to your home. Succulents certainly come to mind. When deciding where to install plants, imagine your home in the bottom of a shallow bowl. The height of your plants should get taller as your move away from the building. This would help draw fire away from your home, rather than towards it. The following plants are less likely to be a fire hazard:

• flowers - French lavender, red monkey flowers, sage, California fuchsia, California lilac, society garlic, coreopsis, California red bud
• shrubs - currants, shrub apples, cotoneaster, bush honeysuckles, and hedging roses
• trees - hardwoods, cherry, maple, poplar

Succulents in a landscape (Kate Russell)

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The added advantage to many of these plants is that they have evolved to withstand drought, which means many of them require less water. UCANR provides a list of low-risk, Fire-safER plants.  Despite their name, evergreens, such as pine and fir, are far more flammable than the hardwoods.


Fire Safety

Create a fire safety plan. If you live in rural areas, use the Wildfire Safety Plan. If you live in a city or suburban area, use the plan provided by the National Fire Protection Association. Seriously, people. It takes 20 minutes and could save your life.


To learn more about how likely fires are in your area, check out the maps provided by the National Park Service. Also, CalFire offers a homeowner’s fire safety checklist that deserves your attention.


In case of high fire risk

If fire risk is especially high, you may want to take the following actions before it is too late:

• remove shrubs that are up against your house (you can always plant new ones later)
• remove vines from any structures
• rake mulch at least five feet away from your home, deck, and other structures

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Fire safe landscape (UCANR)

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Bottom line: keep your plants green and healthy and move flammables away from your home.


Above all else, in case of fire: GET OUT AND STAY OUT. Everything else is temporary.