
Spring is almost here and time to get out and start doing
some yard work. As I stand in front of all of the different types of mulch at
my local home repair store, I can’t decide which one to use. Which one will be
the safest? Which one will last the longest? Which one will look the best the
longest? Which one will be the safest? I know, I already mentioned that one but
being a firefighter by trade, these things cross my mind -- a lot!
There are many choices to use to beautify your landscaping.
There are wood chips, pine bark, pine needles, shredded rubber and more. But
which one is the safest? I asked an employee in the garden section if he knew
of any fire spread ratings of any of the mulches in the store and he looked at
me with a blank, faraway, confused look. So, I decided to look into this
myself.
Mulch has many positive attributes. It reduces the water
requirements of plants, cools the soil temperature, controls weeds and soil
erosion, and visually enhances the landscape. But a major drawback is that many
are combustible, which presents a huge problem in fire prone areas. Embers from
an approaching wildfire can ignite areas where mulch is used. If these areas
are adjacent to the home, it could be wind up to be a disastrous mix.
An evaluation of mulch combustibility was performed in 2008 by
the Carson City Fire Department, the Nevada Tahoe Conservation District, the
University of California Cooperative Extension, and the University of Nevada
Cooperation Extension. The results from this project offer recommendations for
uses of mulches in wildfire hazard areas. Mulch can be defined as any material
that is used to cover the soil surface for a variety of purposes. They can be
classified as organic or inorganic. Organic mulches usually come from plant
materials and include pine needles, pine bark nuggets, shredded western cedar
and even ground or shredded rubber. Inorganic mulches consist of rock, gravel
and brick chips. These inorganic mulches tend not to burn and are safe to use
in any setting.
Eight mulch treatments were evaluated for three
characteristics: flame height, rate of fire spread and temperature. On the test
day, the National Fire Danger Rating System value was Extreme. All eight
mulches were found to be combustible but varied considerably in the three areas
measured.
- Shredded rubber, pine needles and shredded
western red cedar showed the greatest potential for all three characteristics.
- Shredded rubber burned at the hottest average temperature
(in excess of 630 degrees F at a height of 4 inches) and produced the greatest
flame length at over 3 feet.
- Shredded western red cedar had the most rapid
rate of spread, traveling at an average rate of 47.9 feet per minute. It also
produced embers that moved beyond the plot perimeter and ignited adjacent mulch
plots.
- Composted wood chips showed the slowest spread
rate and the shortest average flame length, usually smoldering.
So what does all of this mean? We have a variety of mulch choices
in our landscaping – and we need to know the best uses for each choice.
Immediately next to your home out to five feet, the best mulch to use is an
inorganic one (rock, brick, pavers) or fire resistant plant materials that are
well watered and maintained. Composted wood chips are the best choice of the
materials tested for residential landscape use. However, they are organic and
will still burn. They do tend to burn at the lowest speed and lowest flame
length. If this material is ignited, it could still ignite siding, plant debris
and other combustible materials. The smoldering of this product could also go
undetected by firefighters during a wildland fire event. Shredded rubber, pine
needles and shredded western red cedar can have their place in your landscaping
design, just further from your home. These materials could be used selectively for
landscaping at least 30’ from your home.
So, with this new information that I have now learned about
mulch, I think I’ll use some nice gravel with a few larger stones for some
accent close to my house and save the other stuff to use away from the house.
You never know when a fire is going to approach your home and I don’t want to lose
the biggest investment I’ll ever make.
Photo: A home in Rockland County, NY, damaged by fire starting in mulch in flower beds, from a white paper, "Mulch Fires: What Should the Label Say," by Thomas Williams and Michael Lane, at Vermont Chapter of International Association of Arson Investigators