Monday, February 25. 2008
Here is an email Greg Rubin sent to the Encinitas fire department on redwood mulch and its performance in the Cedar fire. His accompanying photos are at the end of this entry. (Published with his permission.)
The shredded redwood bark mulch is composed of the outer fibrous bark of the redwood tree and is a byproduct of the milling process. There is much documentation available as to the natural fire resistance of redwood trees due to this layer of bark. It has become part of the standard operating procedure for installing native landscapes, because of its unparalleled erosion control, longevity (7-10 years), ecological benefit (tannic acids), and above all else, its fire resistance.
We generally apply the mulch 3-4" thick. What is important is that the mulch quickly consolidates down to less than 1" thick, making for a poorly oxygenated fuel. To encourage this process, we usually hydrate the mulch several days a week for several weeks (we have not yet begun this process at Lux because of the presence of work crews.).
Our experience, both with our own informal testing and real world field observations is that at best the consolidated mulch simply smolders with little flame height. The smoldering mulch is easily kicked out or raked toward the black to stop its spread. The Elfin Forest Fire Department agreed with our assesment and allowed us to use this mulch on their substantial native landscape at the fire station. We have also landscaped the LA City Fire Academy in Elysian park near Dodger Stadium..
Although there is little research into the flammability of this product, in our experience, this mulch has proven to be very fire resistant, and I am including pictures of its performance in the Cedar and Witch fires. We have never lost a home to fire, even though many of our customers were in the direct path of the flames and in some cases were the last structures standing on their street.
We attribute this outstanding success in part to the performance of the mulch - note the attached photos. Note in particular the presence of plastic marker flags in some of the photos. These photos were taken immediately after the 2003 Cedar fire. The plastic flages are unburned and in most cases not even slightly melted! These happened to be placed by the customer to mark a new planting prior to the fires, and show how little flame height was generated by the mulch. This is further born out by the very low scorch marks on the screed line of the house (less than an 2 inches). Ironically, one of the melted sprinkler heads left a much larger scorch mark! And one of the flags started to melt due to a burning garden hose. Also note that not all of the mulch burned. The last photo shows the view out the client's rear window, to illustrate that they were in fact in the middle of the Cedar fire.
I will send an additional email showing damage due to the Witch fire in Ramona and Poway. Althought the landscapes are somewhat scorched (though not dead), the houses were completely defensible and saved every time. Some of the houses did not even have the benefit of fire-fighters, yet the houses were unburned. On the other hand, some of the neighbors burned to the ground despite being completely cleared to mineral soil (in one case about 300 feet) and/or still surrounded with bright green lawn.
I hope this information helps alleviate concerns about the use of this mulch. It is absolutely essential for the health of the native landscape, erosion control, and fire resistance, and has become a standard operating procedure with native plants. Please contact me if you need any additional information.
President and Chief Designer
California's Own Native Landscape Design, Inc,
Click on a photo to see it larger.