It's springtime, and many of us are adding new plants to our gardens.  That means it is also a good time to review the principles of creating defensible space around our homes.

Fire is a normal part of the natural environment in California, so if you live in the wildland-urban interface (WUI), it's not so much a question of if, but of when your home will be exposed to wildfire.  With this thought and the devastation of the Camp Fire and other recent Northern California fires in mind, many Butte County property owners may be thinking about creating a fire-resistant landscape around their homes.  Not only is this a prudent course of action, a 2005 revision of the California Public Resources Code (PRC 4291) requires that property owners create 100 feet (or to the property line) of defensible space around homes and buildings.  Defensible space is defined as the area around a structure where the landscape is designed and maintained to decrease fire danger.  Creating defensible space also gives firefighters an opportunity to safely protect your home. 

The key to establishing defensible space is to utilize plants that are fire resistant and judiciously space them both horizontally and vertically. Increasing the space between plants limits the ability of fire to spread.  As a rule of thumb, Cal Fire recommends that on flat ground the space from the edge of one shrub to the edge of the next be twice the height of the shrub.  For example, if shrubs are two feet tall, they should be spaced four feet apart.  If the shrubs are growing on a moderate slope the space between them should be four times the height of the shrub.  The space between trees should be 10 feet from canopy to canopy and increase to 20 feet on a moderate slope.

If a fire reaches the crown of a tree, its heat intensity increases and this can increase the combustibility of surrounding vegetation.  Low tree branches create fuel ladders that allow fires to climb into a tree.  To prevent fires from ‘crowning,' these ladder fuels must be eliminated.  Cal Fire recommends that the lower branches of a mature tree should be pruned to create a clearance of three times the height of the shrubs beneath it.  For example if a shrub is four feet tall, the tree should be pruned so that there is 12 feet of clearance between the top of the shrub and the lowest branches of the tree.  For younger trees, the lower one-third of branches should be removed.

The area that is 30 feet closest to a home is often called the “home defense zone” or, as Cal Fire puts it, the “Lean, Clean and Green Zone.”  In this area, highly flammable fuels should be eliminated or minimized and widely spaced plants should be kept green and well irrigated.  Vegetation in this zone should be comprised of shorter plants such as grasses and non-woody flowers.  If shrubs or trees are planted, they should be fire-resistant plants such as deciduous trees (which shed their leaves in the fall) or non-woody natives and other perennials such as salvias.  Fire-resistant ground covers are also an acceptable choice for this area.  Avoid planting broadleaf evergreens (like holly and coyote bush), conifers (like pines, junipers, cedars, and firs) and palms, because they are highly flammable. 

Applying mulch is a good strategy for conserving soil water, reducing weeds and preventing erosion.  Normally, materials such as wood chips, shredded bark, leaves or straw are used as mulches because these organic materials have the added benefit of enriching the soil and improving its water-holding capacity.  However, organic materials burn, so within the five feet closest to a home, it is recommended that non-combustible mulches of rock, gravel, pavers or broken concrete be used instead of traditional organic materials.

When planning a firewise landscape, the contribution of hardscape features should not be overlooked.  Decomposed granite, cement, asphalt or gravel pathways and driveways make effective firebreaks.  Structures such as patios and masonry walls and water features like pools, ponds, and streams will also impede the advance of a fire. 

Before moving beyond the 30-foot home defense zone, mention should be made of items that do not belong too close to a home.  Most propane tanks should be located a minimum of 10 feet from any structure, and woodpiles should be at least 30 feet away.  A cord of seasoned firewood contains the energy equivalent of approximately 174 gallons of gasoline!  Would you store that much gasoline on your porch?  Also, flammable liquids such as gasoline, paint thinner, and turpentine should be properly stored away from ignition sources and combustibles.

The outer 70 feet of the defensible space is called the “reduced fuel zone.”  As with the home defense zone, plants in this zone should be well spaced horizontally and separated vertically to eliminate fire ladders.   Fire resistant plants should also be used here.  Most surface litter such as leaves, pine needles, and twigs should be removed so that this layer is no more than three inches deep.  Dead annual grasses should be mowed to a height of no more than four inches.  Mature trees without shrubs growing beneath them should be limbed to a height of six feet above the ground.  All plants should receive adequate water and dead branches in trees and shrubs should be regularly removed.  As noted in the UC Cooperative Extension's fact sheet on defensible space, “The goal of brush clearance is not to remove all vegetation.  When done well, cleared areas should still include enough well-spaced and judiciously pruned plants to protect against excessive erosion and provide wildlife habitat.”

If organic mulches are used in the reduced-fuel zone, a 2008 study showed that a mulch of composted wood chips spread two to three inches deep showed the slowest fire-spread rate of the eight mulches tested.  A potential disadvantage of wood chip mulches is that they tend to smolder and can be difficult to extinguish.  In general, fine, stringy mulches such as shredded bark burn more rapidly than larger chunks.

Establishing defensible space can be summarized by the following three R's:  1) Remove dead and dying plant material; 2) Reduce the density of vegetation and ladder fuels; 3) Replace hazardous vegetation with less flammable, well-irrigated fire resistant plants.

Further information on fire safety for homeowners can be found on the Cal Fire website at Home - Ready for Wildfire.  And for property owners who are considering landscaping from scratch, the Sonoma-Marin Saving Water Partnership has developed eight fire-rebuild landscape design plans that are well worth considering (Water Smart Landscape Design Templates - Sonoma- Marin Saving Water Partnership).

For more information on creating fire resistant landscapes, attend our Firewise Gardening workshop on May 2, part of the Master Gardeners' 2024 Spring Workshop Series. For information about all the workshops, and to register, visit our website.  All workshops are free, but registration is required.

Why not buy some plants for your fire-resistant landscape at the Master Gardeners' Plant Sale on Saturday, May 18, 2024? The sale will be held at our Demonstration Garden at Patrick Ranch, 10381 Midway, between Chico and Durham, from 9 am till noon. For more information, and a partial list of plants, see our Plant Sale webpage.  

UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system.  To learn more about us and our upcoming events, and for help with gardening in our area visit our website.  If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at 530-552-5812. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us section of our website.

Even when homeowners have created a defensible space, the job of protecting their home from fire is never done.  There will always be ongoing and annual jobs to do.  Additionally, there are special tasks that will need to be completed every few years or on an as needed basis.

A key ongoing yard maintenance goal is to keep plants green and lush, especially within the 30 feet closest to the home (the “home ignition zone”).  Of course this means regular watering, which can be time consuming, but employing a drip irrigation system on a timer largely eliminates that concern.  Using appropriate native plants should cut down on the overall need for watering as well. 

The ground in the inner 30 feet around a home should also be kept free of leaves, pine needles, weeds and other ground fuels.  Dead plants and/or tree branches should be immediately removed, as should any tree branches overhanging the roof.  Tree branches should also be kept at least 10 feet away from a chimney.  Vines growing on trees, shrubs, or fences can act as fire ladders and should be removed.  Roofs and gutters should be kept free of leaves, needles and twigs.  Gutter covers can reduce, if not eliminate, fuel build-up in this area. 

If raised decks or porches are present, prevent combustible materials from accumulating in the areas beneath them.  A preferable alternative to continually raking under decks and porches is to screen or enclose them with fire-resistant materials.  If screening is used, the mesh should be no greater than one-quarter-inch.  Flammable materials should be cleared from decks.  This includes not only natural materials like leaves and needles, but items such as brooms and stacked wood.

Annually, before fire season starts, grasses and weeds should be mowed to a height of about three to four inches for at least 30 feet around homes and other structures. Grasses and weeds should be maintained at this height throughout the fire season.  In fact, ground fuels should be kept at a minimum throughout the defensible space.  As an alternative to mowing, string trimmers are a safer option for vegetation removal.  To reduce the risk of fire due to mowing, make sure your equipment is properly maintained, mow before 10 a.m. and never mow on a hot or windy day. 

Vegetation throughout the defensible space should be pruned for proper spacing, both vertically and horizontally, at least once per year.  Cal Fire recommends that the lower branches of a mature tree be pruned to create a clearance of three times the height of the shrubs beneath it, while the distance between shrubs should be at least twice the height of the shrubs. In addition to maintaining proper spacing, pruning also makes plants more fire resistant.  Cutting back woody perennials encourages less flammable new growth and thinning overgrown shrubs reduces their fuel load.  Avoid topping landscape trees.  Topping not only increases the fire hazard by encouraging excessive branching, but it is not healthy for trees.

Woodpiles should be located at least 30 feet from a home and should have at least 10 feet of cleared space around them.  Covering a woodpile, or storing wood in a fire-resistant structure such as a metal shed, lowers the odds of the pile igniting during a wildfire.  In addition, miscellaneous combustible materials including construction debris and brush piles should be removed from your yard as quickly as possible.

To aid firefighters, be sure your address is clearly posted so that it is easily visible from the street, especially at night.  Also, be certain firefighters have easy access to water sources in your yard and, if possible, clearly mark those water sources.  Fires often lead to power outages, so if you are on a well, it would be prudent to have an emergency generator to operate the pump if the power does fail.

Cal Fire has developed a “Homeowners Checklist” that describes how to make your home fire safe.  It is an excellent, easy-to-use, comprehensive guide for homeowners. It is highly recommended.  For more information on creating fire-resistant landscapes, see the Firewise Landscape section of the UC Master Gardeners of Butte County website.  Other helpful sources include Yard Maintenance by UC Master Gardeners of Sonoma County and defensible space tips by the Butte County Fire Safe Council.  

UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu (preferred) or call (530) 538-7201.

The devastating Camp Fire of 2018, along with the numerous fires North State residents have experienced since then, have led many of us to focus on creating a defensible fire-resistant landscape around our homes.   As noted in this column last Friday, the key to establishing defensible space is to utilize plants that are fire resistant and judiciously space them both horizontally and vertically.          

The good news that some plants are more fire-resistant than others, but it must be emphasized that fire-resistant plants are not fireproof!  It is important to realize that creating a “firewise” landscape entails much more than choosing the right plants.  Still, a working knowledge of fire-resistant plants is a good starting point for creating a firewise landscape.  Fire resistant plants are relatively slow to ignite and tend to have certain characteristics in common.  They have moist, supple leaves and their watery sap usually lacks a strong odor.  Fire resistant plants also tend not to accumulate dry, dead material within or beneath the plant.  Plants that are slow growing will accumulate fuel at a slower pace, so they require less maintenance.  Native species can play a role in firewise landscaping as well.  Drought tolerant native plants often maintain a high internal water content without needing much water and native trees commonly have a high tolerance for fire.  Native trees may also restrict the growth of more volatile invasive species.

Examples of fire-resistant ground covers include ajuga, creeping thyme, creeping phlox, wild strawberry, snow-in-summer, sedums, hen & chicks and California fuchsia.  Some fire-resistant flowering plants are yarrow, allium, columbine, coreopsis, delphinium, gaillardia, daylily, iris, lavender, Echinacea, lupine, poppies, penstemon, salvias (which are exceptions to the aromatic sap guideline), lamb's ear, evening primrose, hosta, coral bells, dusty miller, and bulbs of all kinds.

Shrubs that are fire resistant include ceanothus, butterfly bush, spirea, rose of Sharon, Oregon grape, lilac, mock orange, potentilla, forsythia, cotoneaster, island bush poppy, currants, camellia, azalea, monkey flower and viburnum.  Aloe and other succulents are generally considered fire-resistant but avoid succulents such as ice plant that produce mats of flammable dry material. 

Choose deciduous trees such as maples, oaks, sweet gum (liquidambar), locust, redbud, dogwood, ash, toyon, and smoke tree.  Citrus and deciduous fruit trees such as cherry, peach and plum are fire resistant.  Although most conifers are highly flammable, redwoods are the exception to the rule and are a desirable tree in a firewise landscape.

Highly flammable plants often have an excess of fine dry or dead material and contain volatile waxes, terpenes, or oils.  Their sap is gummy or resinous and aromatic.  They may have loose, papery bark as well.  Examples of flammable plants are sagebrush, conifers (cedar, pine, juniper, fir, Italian cypress), broom, rosemary, eucalyptus, palms, feather and fountain grasses and dry annual grasses.  These plants should be avoided when planning a firewise landscape; if they already exist in a landscape, consideration should be given to removing them. 

For more information on creating fire resistant landscapes, see the Firewise Landscape section of our website.

UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu (preferred) or call (530) 538-7201.

Fire is a normal part of the natural environment in California, so if you live in the wildland-urban interface (WUI), it's not so much a question of if, but of when your home will be exposed to wildfire.  With this thought and the devastation of the Camp Fire and other recent Northern California fires in mind, many Butte County property owners may be thinking about creating a fire-resistant landscape around their homes.  Not only is this a prudent course of action, a 2005 revision of the California Public Resources Code (PRC 4291) requires that property owners create 100 feet (or to the property line) of defensible space around homes and buildings.  Defensible space is defined as the area around a structure where the landscape is designed and maintained to decrease fire danger.  Creating defensible space also gives firefighters an opportunity to safely protect your home. 

The key to establishing defensible space is to utilize plants that are fire resistant and judiciously space them both horizontally and vertically. Increasing the space between plants limits the ability of fire to spread.  As a rule of thumb, Cal Fire recommends that on flat ground the space from the edge of one shrub to the edge of the next be twice the height of the shrub.  For example, if shrubs are two feet tall, they should be spaced four feet apart.  If the shrubs are growing on a moderate slope the space between them should be four times the height of the shrub.  The space between trees should be 10 feet from canopy to canopy and increase to 20 feet on a moderate slope.

If a fire reaches the crown of a tree, its heat intensity increases and this can increase the combustibility of surrounding vegetation.  Low tree branches create fuel ladders that allow fires to climb into a tree.  To prevent fires from ‘crowning,' these ladder fuels must be eliminated.  Cal Fire recommends that the lower branches of a mature tree should be pruned to create a clearance of three times the height of the shrubs beneath it.  For example if a shrub is four feet tall, the tree should be pruned so that there is 12 feet of clearance between the top of the shrub and the lowest branches of the tree.  For younger trees, the lower one-third of branches should be removed.

The area that is 30 feet closest to a home is often called the “home defense zone” or, as Cal Fire puts it, the “Lean, Clean and Green Zone.”  In this area, highly flammable fuels should be eliminated or minimized and widely spaced plants should be kept green and well irrigated.  Vegetation in this zone should be comprised of shorter plants such as grasses and non-woody flowers.  If shrubs or trees are planted, they should be fire-resistant plants such as deciduous trees (which shed their leaves in the fall) or non-woody natives and other perennials such as salvias.  Fire-resistant ground covers are also an acceptable choice for this area.  Avoid planting broadleaf evergreens (like holly and coyote bush), conifers (like pines, junipers, cedars, and firs) and palms, because they are highly flammable. 

Applying mulch is a good strategy for conserving soil water, reducing weeds and preventing erosion.  Normally, materials such as wood chips, shredded bark, leaves or straw are used as mulches because these organic materials have the added benefit of enriching the soil and improving its water-holding capacity.  However, organic materials burn, so within the five feet closest to a home, it is recommended that non-combustible mulches of rock, gravel, pavers or broken concrete be used instead of traditional organic materials.

When planning a firewise landscape, the contribution of hardscape features should not be overlooked.  Decomposed granite, cement, asphalt or gravel pathways and driveways make effective firebreaks.  Structures such as patios and masonry walls and water features like pools, ponds, and streams will also impede the advance of a fire. 

Before moving beyond the 30-foot home defense zone, mention should be made of items that do not belong too close to a home.  Most propane tanks should be located a minimum of 10 feet from any structure, and woodpiles should be at least 30 feet away.  A cord of seasoned firewood contains the energy equivalent of approximately 174 gallons of gasoline!  Would you store that much gasoline on your porch?  Also, flammable liquids such as gasoline, paint thinner, and turpentine should be properly stored away from ignition sources and combustibles.

The outer 70 feet of the defensible space is called the “reduced fuel zone.”  As with the home defense zone, plants in this zone should be well spaced horizontally and separated vertically to eliminate fire ladders.  Fire resistant plants should also be used here.  Most surface litter such as leaves, pine needles, and twigs should be removed so that this layer is no more than three inches deep.  Dead annual grasses should be mowed to a height of no more than four inches.  Mature trees without shrubs growing beneath them should be limbed to a height of six feet above the ground.  All plants should receive adequate water and dead branches in trees and shrubs should be regularly removed.  As noted in the UC Cooperative Extension's fact sheet on defensible space, “The goal of brush clearance is not to remove all vegetation.  When done well, cleared areas should still include enough well-spaced and judiciously pruned plants to protect against excessive erosion and provide wildlife habitat.”

If organic mulches are used in the reduced-fuel zone, a 2008 study showed that a mulch of composted wood chips spread two to three inches deep showed the slowest fire-spread rate of the eight mulches tested.  A potential disadvantage of wood chip mulches is that they tend to smolder and can be difficult to extinguish.  In general, fine, stringy mulches such as shredded bark burn more rapidly than larger chunks.

Establishing defensible space can be summarized by the following three R's:  1) Remove dead and dying plant material; 2) Reduce the density of vegetation and ladder fuels; 3) Replace hazardous vegetation with less flammable, well-irrigated fire resistant plants.

Further information on fire safety for homeowners can be found on the Cal Fire website at Home - Ready for Wildfire.  And for property owners who are considering landscaping from scratch, the Sonoma-Marin Saving Water Partnership has developed eight fire-rebuild landscape design plans that are well worth considering.

For more information on creating fire resistant landscapes, see the Fire-Safe Landscape section of UC Master Gardeners of Butte County website, and the UC ANR publication Home Landscaping for Fire (PDF).

Watch this space!  Next week's Real Dirt will focus on plants that are fire resistant.

UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu (preferred) or call (530) 538-7201.