Marin Master Gardeners
University of California
Marin Master Gardeners

Fire-smart Landscaping - Defensible Space

Defensible Space and Your Garden

Photo credit: National Fire Protection Association
Photo credit: National Fire Protection Association

Defensible space quick check list:

  • Start at the house and work out
  • Know your evacuation route and clear it of overgrown vegetation
  • Ensure maneuvering space for firefighters
  • Break up fuel by creating space between plants, and between the ground and the branches of trees
  • As you evaluate your property, consider the size, location, structure and condition of your plants
  • 0’ – 5’: No flammable mulch, fencing, furnishings, no dead branches, no roof litter, no tall plants under eaves (flames rise 2-3x) nothing flammable attached to house, no branches within 1-‘ of roof or chimney
  • 5’ and beyond: 5’ from house, low, well-irrigated plants, 10’ from house, large shrubs and trees, 30’ from house wood mulch. Use hardscape as fuel breaks between plantings, space plants to be accessible for maintenance, allow vertical and horizontal space between shrubs and trees, especially on slopes
  • Keep your gutters and roofs clear of leaves and debris
  • Mow grass to a height of 4 inches
  • Keep mulch away from the structure.
  • During a wildfire move anything burnable such as patio furniture or gas BBQ tanks 30 feet away from structures.
  • Work with neighbors to create defensible spaces throughout the neighborhood

Zoning: The concept of zoning, with increasing attention to fire safety in zones closer to the house, is central to fire-smart landscape design.   An appropriately landscaped and maintained defensible space will reduce the fire risk to structures and provide an area for fire fighters to protect your home. Defensible space uses the judicious selection and placement of plantings as a strategy to decrease the spread of fire.

Maintenance: The significance of proper plant and landscape maintenance cannot be overemphasized. Poorly maintained landscapes can easily become fire hazards even if many of the plants are favorably recommended for fire performance. 

Encouraging healthy growth by lopping off dead material, clearing out accumulated debris, properly watering and fertilizing plants is essential to the idea of defensible space. The positioning of plants relative to each other and structures is also very important. Removal of any potential fuel ladders needs to be part of routine landscape maintenance.

Defensible Space: Landscapes can be designed and reworked to provide defensible space and reduce fire hazard.  All vegetation, including native plants and ornamental plants, are potential fire fuel. Through proper planning and ongoing maintenance, you can have both a beautiful landscape and a fire wise home. Fire-smart landscapes should also include hardscape, such as granite paths and stone walls.  These can act as fuel break and help to slow down or change the path of an approaching fire.  Following are recommended best practices for defensible space.

Balancing your Fire-smart gardening budget: If expense is a consideration, start small.  Do what you can.  Work with your neighbors to seek help with labor and materials.  Buying in bulk is a way to reduce cost.  Start small by introducing or replacing combustible plants with non-combustible materials to restrict the spread of fire

Zone 0, 0 feet to 5 feet from structures, is the innermost zone and should be the most fire-resistant area.  The goal is to avoid home ignition from blowing embers. 

  • Zone 0 is a good place for noncombustible materials such as walkways or a patio of concrete, brick, paving stones, decomposed granite or gravel mulch.
  • Shrubs and trees are not recommended in the 5-foot zone
  • Remove dead vegetation and implement a maintenance strategy to keep the 5-foot zone clear of dead plant materials
  • Remove leaves and needles from roof and gutters.
  • Plants against combustible siding or under a window present the greatest hazard since their flames can make direct contact with the siding and can cause vertical flame spread
  • Clear vegetation and combustible items around and under a deck or under an overhang.
  • Firewood and other combustible materials should not be stored in this critical area.
  • No bark chips. Bark chips retain soil moisture, but they are combustible and provide fuel for smoldering embers.

Zone 1, 5 feet to 30 feet from structures. The objective of this zone is to reduce heat and movement of flame.

Zone 1 is a good place for a water element, pool, or a patio of concrete, brick, paving stones, decomposed granite or gravel mulch.   Try to have plants that are small and in clusters that are well spaced.  The closer to the home, the smaller the plants and clusters should be.  Walkways through this zone can help separate planting areas while also simplifying maintenance. Walkways should be four to five feet wide and may be gravel, brick, concrete, compacted earth, or decomposed granite.   We like to think of this area as Lean, Clean and Green:

  • Lean
    • well-spaced groupings with room to prune out dead vegetation
    • shrubs under trees should be avoided
    • low growing shrubs, non-woody low growing perennials and groundcovers on drip irrigation
    • avoid extensive use of mulch which can convey fire to the house
    • incorporate hardscape which can act as fuel breaks
  • Clean
    • remove dead vegetation especially during the dry season
    • remove dead trees and fallen branches
    • remove pine needles and fallen leaves
    • trees, if any, should be small and they should not accumulate or drop more dead material than can be consistently removed from the site.
    • relocate wood piles outside this zone
    • relocate large gas and propane tanks outside this zone
  • Green
    • plants are healthy and green during fire season
    • replace struggling plants with plants that will remain green and lush; healthy plants with a high moisture content are more difficult to ignite

Zone 2 is thirty to one hundred feet from structures.  The objective of this area is to decrease the energy and speed of the fire by eliminating continuous, dense vegetation, both vertically and horizontally. This is a transition zone on larger lots. This is the space between manicured gardens adjacent to the house and fringe areas abutting open space or between groups of houses surrounded by open space.

  • larger shrubs and trees in this zone should be planted in widely spaced groups separated by areas of mulch or low groundcovers that break up the path of fire.
  • choose low-growing, irrigated, non-woody plants such as vegetables, succulents, erosion-control grasses, flowers, or lawn to create landscaping in this zone
  • larger plants should be spaced widely and interspersed with lower plantings. The taller the plants, the more widely they should be spaced
  • trim trees regularly to maintain a mimimum of 10 feet of clearance between branches of adjoining trees or shrubs. Clumps of several trees may be treated as a single tree.
  • mow any grass to a maximum height of 4 inches
  • at further distance from the home, plants may not be irrigated, but they should be well maintained
  • native vegetation with low water usage can be a good choice

Other things to consider:

Vegetation on Slopes – Assess the hazards in your surroundings. Is your home on a grassy hillside or in a wooded canyon? Fire tends to travel fastest uphill by preheating dried vegetation from below and making it easier to ignite. The steeper the slope, the faster a fire will spread. Narrow canyons and saddles act as chimneys that trap heat, channel wind, and create erratic fire behavior. Ridges are also fire-prone. Heavily vegetated slopes are particularly hazardous.

  • If there is horizontal space between the slope and your home, consider constructing a stone or concrete wall between your house and the most likely path of approaching fire to help deflect flames, heat, and burning embers away from the house. This is also a good place to install a lawn, a pool, or a patio of non-flammable materials such as concrete, brick, or stone.
  • Vegetation on slopes should be low in both height and volume but should not be completely eliminated because bare slopes may be subject to erosion and instability. Remove dead trees and shrubs, leaving the roots in place, if practical
  • A good slope planting consists of widely spaced deep-rooted shrubs interspersed with mulch or low- growing groundcovers.
  • Use retaining walls to reduce the steepness of slopes below the house. This may slow the spread of fire and also help to prevent erosion and slope instability.

Structures

  • Trellises, gazebos, sheds, and other structures should be located in such a way that they do not serve as a path for fire. Construction materials and methods for these structures should be as fire-resistant as for homes. Trellises, for example, can be made of steel, and roofs of gazebos and sheds should meet roofing standards for homes
  • Work with neighbors to create 100’ of defensible space

Reference Materials for further reading

Wildfire Preparation & Recovery: https://ucanr.edu/sites/fire/PrePost/

Defensible Space: https://ucanr.edu/sites/fire/PrePost/Landscaping/DefensibleSpace/

Maintain Defensible Space: https://disastersafety.org/wildfire/defensible-space/

East Bay Municipal Utility District Fire Scaping:  https://www.ebmud.com/water/conservation-and-rebates/watersmart-gardener/firescaping/

Fire Information Engine Toolkit: https://ucanr.edu/sites/fire/files/284898.pdf

Community Action & Involvement: https://ucanr.edu/sites/fire/PrePost/Community/

Creating Defensible Space to Help Survive a Wildfire Ember Storm:  https://cafiresafecouncil.org/resources/fire-safety-information-for-residents/

Fire Science & Ecology: https://ucanr.edu/sites/fire/Ecology/

The Fire Ecology of California: http://sonomamg.ucanr.edu/Firewise_Landscaping/The_Fire_Ecology_of_California/

FireSafe Marin:  https://firesafemarin.org/preparedness

Webmaster Email: banielsen@ucanr.edu