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Fall Is Mulching Time
By Mark Mandelbaum
Landscape mulches come in wide arrays of colors and textures. Pine straw is common in some areas, shredded hardwood bark in others. Mulches can even be cocoa hulls or gravel. They help conserve moisture and suppress weeds, but how well they do those jobs, or how often they need to be replenished, varies from mulch to mulch, according to Susan Day, professor at Virginia Tech. Research shows that mulches also benefit the environment by reducing erosion.
David Mitchell, a graduate student working with Day, studied how mulches affect water runoff and sediment transport. He studied eight mulch types and measured their performance. Following are some of the preliminary results from his study.
First, all mulches have a huge effect on total suspended solids running off site. Bare soil lost about five times more sediment than soils with mulches covering them. Thus, mulches help control erosion.
Second, geotextiles underneath mulches (such as “landscape fabric” meant to suppress weeds) appeared to accelerate water runoff in Mitchell’s studies.
Finally, each type of mulch wears differently, and absorbs a lot of runoff on its own, independent of the soil beneath it.
“Think of mulch as a temporary forest floor,” says Day. “It affects the traditional realms of aesthetics, moisture conservation, and elimination of competition for desired plants. But, it is also an important cog in the machinery of the water cycle by keeping the soil surface receptive to water. This improves water quality by allowing the water to soak into the soil, instead of [running off and requiring] a stormwater control system. Soil is an important part of the water cleansing cycle.”
The right mulch can:
- Suppress weeds
- Help soil retain moisture
- Reduce water runoff
- Reduce erosion of sediments
- Provide aesthetic value
Day is a professor in the departments of Horticulture and Forest Services/Environmental Conservation at Virginia Tech in Blacksburg, Virginia. See more at: http://www.vt.edu/
This material is excerpted from a blog post on Soils Matter, a public service of the Soil Science Society of America. Soils Matter subjects are written to help the public understand that soil is a precious natural resource, http://soilsmatter.wordpress.com/. SSSA has additional soils information for the public on their www.soils.org/discover-soils website, a website for teachers, www.soils4teachers.org, and for students through 12th grade, www.soils4kids.org.
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