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Be Ember Aware Tip #8: Much Ado About Mulches

Posted 6/15/2009

Note: This is the eighth in an ongoing series of tips for homeowners living in fire-prone areas. Each week, Cooperative Extension Natural Resource Specialist Ed Smith will be providing Be Ember Aware tips for homeowners who want to reduce the risk of losing their home to embers created from wildfires. Nevada has more than 250 communities that face a wildfire threat, and 68 communities are at extreme and high risk. For more information on protecting your home from wildfires, visit Living With Fire.

By: Ed Smith, natural resource specialist, University of Nevada Cooperative Extension

Mulches play an important role in northern Nevada landscapes. They can reduce the water requirements of plants, cool soil temperatures, reduce the occurrence of weeds, control soil erosion and dust, and can visually enhance the landscape. Unfortunately, some popular mulches are also combustible, a bad attribute for residential landscapes located in high fire hazard areas, and can be easily ignited by embers during a wildfire.

Organic mulches are made from plant materials. Examples include pine needles; wheat straw; pine bark nuggets of various sizes; shredded western red cedar and redwood, sometimes referred to as "gorilla hair;" and wood chips from recycled pallets or wildfire fuel-reduction projects. These materials vary considerably in terms of size, shape and texture, and these qualities also influence their flammability.

Experiments conducted by the University of Nevada Cooperative Extension, Nevada Tahoe Conservation District and Carson City Fire Department indicate that pine needle and gorilla hair mulches pose the greatest fire hazard of the organic mulches. Test results show that they are easily ignited, burn fast, and produce considerable heat. Other organic mulches, such as bark nuggets and wood chips, burn somewhat slower but produce considerable heat. Partially composted wood chips produce very little flame and burn much slower than the other mulches, but burn hot via glowing combustion.

Inorganic mulches are derived from non-plant materials and include rock, stone and gravel. Most inorganic mulches are noncombustible and are good choices for homes located in high fire hazard areas. The important exception would be ground or shredded rubber. Rubber mulch products, which are often used in playgrounds, burn very intensely and are difficult to extinguish.

Some important mulch tips for homeowners living in high fire hazard areas are:

  • Do not use organic mulches within 3-5 feet of the house. This is particularly important for wood-sided houses. During a wildfire, burning embers may accumulate in this area, providing ample sources of ignition for wood and bark mulches.
  • Keep organic mulches at least several feet away from combustible materials such as wood posts, firewood stacks, wooden fences, decks, stairs, etc.
  • Irrigating organic mulches, as in a flowerbed, may improve their ignition resistance.
  • Do not allow thick layers of pine needles to accumulate within 30 feet of the house.
  • Do not use ground rubber mulches within 30 feet of the house or deck.
  • Near the home, emphasize the use of inorganic mulches such as rock and gravel.

To learn more about protecting your home from the ember threat, visit Living With Fire and request a free copy of our new publication, Be Ember Aware! You can also download it at University of Nevada Cooperative Extension or contact Ed Smith. Be Ember Aware is a component of the Living With Fire program, an interagency program coordinated by University of Nevada Cooperative Extension.

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