Marin Master Gardeners
University of California
Marin Master Gardeners

Fire-smart Landscaping - Hardscape

Hardscape, combustible and non-combustible mulches

Hardscape and mulch quick check list

  • 0’-5’ non-combustible mulch only
  • Mulch layer thickness should not exceed 3”
  • Eliminate continuous fire paths by separating wood mulch with non-combustible mulch or hardscape
  • Use combustible mulch wisely

Permeable Hardscape. Source: UCANR
Permeable Hardscape. Source: UCANR
Hardscapes are the constructed features such as paths, patios and pergolas that make a landscape human-friendly.   Landscape Architects and others in the landscape design field use the terms “softscape” and “hardscape” to distinguish between plants and soil work and all the other “hard” elements of landscaping. A simple definition of “hardscape” is anything in the landscape that is not plantings or earth works. 

Combustible mulches are wood.  The thickness of the mulch bed, wind speed, and location of the flame and building all impact the potential of mulch to ignite and how quickly fire can spread to the structures on the property.

Non-combustible mulches include noncombustible rock, gravel, concrete and pavers. 

Guidelines

  • 0’ - 5’ Non-combustible mulches
  • 5’ – 30’
    • Composted wood chips – these demonstrated the least hazardous fire behavior in testing and would be the best choice for use in residential landscapes. However they are still considered a combustible materials and could ignite wood siding, plant debris and other combustible materials in contact with or immediately adjacent to the mulch bed. 
    • Notes:
      • do not use in widespread or continuous manner
      • separate areas mulched with these materials with noncombustible and ignition-resistant materials such as concrete, gravel, rock and lawn
    • In general, fine (less than ¼” particles) or stringy mulches ignite and burn more rapidly than larger chunks.
    • When exposed to fire, thick mulch layers (greater than 2-3” deep) tend to smolder and are difficult to extinguish.
    • Burning mulch generates embers that can ignite nearby mulch, increasing the changes of direct flame contact spreading to the structure.

Reference Materials for further reading

The Combustibility of Landscape Mulches: https://ucanr.edu/sites/MarinMG/files/321642.pdf

Choose Your Mulch Wisely:  http://marinmg.ucanr.edu/files/237709.pdf

Immediate (NonCombustible) Zone: ibhs.org

Mulch – a Gardeners Best Friend:  http://sonomamg.ucanr.edu/Sonoma_Gardener_Articles/Mulch--a_Gardeners_Best_Friend/

Webmaster Email: banielsen@ucanr.edu