Fire Safe Gardening

We all think it won’t happen to us. Fires happen elsewhere, to other people. And then fire strikes closer to home, devastating everything in its path. The time to protect your home and your family is before temperatures rise. The time to garden for fire safety is now.

Raging wildfire (National Weather Service, NOAA) Public Domain

Drought and climate change have killed hundreds of millions of mature trees in North America. In California alone, over 102 million trees died between 2010 and 2017. Many of the remaining trees are not as healthy as they could be. Trees weakened by drought, disease, and bark beetle infestations are more susceptible to fire.

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 a fire to move through your landscape using shrubs and trees as a superhighway, you can create spaces that slow or stop the flames. 

Many state laws require that rural homes have a 100-foot defensible space. Suburban homes face different challenges, but fire safety is still critical. Many of the suggestions still apply. Since each county has its own set of ordinances, check with local authorities. Even without the law, fire safety around your home simply 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. That space consists of two zones: 

Zone 1 is a 30-foot perimeter around any structures. You can prevent fire in this zone with these tips:

1. Remove all dead vegetation.
2. Remove dry leaves and pine needles from the roof and rain gutters.
3. Prune tree branches to keep them 10 feet away from your home and each other.
4. Move patio furniture and other flammables away from trees and shrubs.
5. Move woodpiles and other flammable materials into Zone 2.

Zone 2 extends 100 feet from your home. Maintain Zone 2 with these practices:

1. Keep grasses mowed to 4 inches or less.
2. Rake up fallen leaves, needles, and twigs.
3. Create horizontal space between shrubs and trees.
4. Create vertical gaps between trees, shrubs, and grasses.

Spacing plants and trees

By creating space between trees and shrubs, the spread of fire can be slowed or stopped. These spaces are vertical (up and down) and horizontal (side to side). To maintain safe vertical space, remove any tree branches less than 6 feet from the ground. 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. For example, a 4-foot shrub would need to be at least 12 feet away from 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. So, 4-foot shrubs should be 8 feet apart to be safe. 
• Slopes of 20 to 40% require shrubs to be four times their height apart, and trees need 20-foot spacing. 
• When working with steeper slopes, trees should be 30-feet apart, and shrubs need to be six times their height apart.

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 groundcover 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. I have listed what they learned below, worst to safest. In each case, the mulch was 2- to 3-inches deep unless stated otherwise:

• Shredded rubber burns the hottest at 630°F and flames the highest (over 3 feet).
• Pine needles spread fire the second-fastest.
• Shredded western red cedar, also known as Gorilla hair, spreads the fastest, at nearly 50 feet per minute, at 380°F, with one-foot flames and many embers.
• Medium pine bark nuggets spread more slowly with moderate flames.
• Tahoe chips, which consist of wood chips, pine needles, and other plant biomass from tree chipping, spreads moderately fast with medium-sized flames.
• Tahoe chips treated with fire retardant only slow the spread of fire by 5 to 10 minutes.
• Tahoe chips applied in a single layer burn at the lowest temperatures and spread the slowest, with the lowest flame height.
• Composted wood chips were the only material that did not “demonstrate active flaming combustion” with only “incidental flaming with smoldering”; spread less than 0.3 feet per minute.

Use fire-resistant plants

We all know that green plants burn more slowly than dead, dry plants. But there are no 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 probably come to mind.

Succulents in a landscape

Imagine your home sitting at the bottom of a shallow bowl. To maintain fire safety, place shorter plants closer to the house and taller plants further away. Doing this helps draw fire away from your home rather than towards it. The following plants are less likely to be a fire hazard:

• Flowers such as French lavender, red monkey flowers, sage, California fuchsia, California lilac, society garlic, coreopsis, and California redbud are good choices.
• Shrubs resistant to fire include currants, shrub apples, bush honeysuckles, and hedging roses.
• Hardwoods, cherry, maple, and poplar trees are also good choices.

The added advantage to many of these plants is that they have evolved to withstand drought, which means many of them will require less water. 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 the risk of fire is high in your area, you may want to take the following actions before it is too late:

1. Remove shrubs that are up against your house. You can always plant new ones later.
2. Remove vines from any structures.
3. Rake mulch at least five feet away from everything.

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​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.