Mulch performs many functions in the home landscape. A cover of mulch reduces weeds, prevents soil erosion and drying, and unifies a yard's disparate elements. Various woods have long provided organic mulch. Rubber mulch made from discarded tires, however, is rapidly gaining a share of the mulch market. Knowing how these different mulch materials compare will let you make the better choice for your home.
Rubber and wood mulches are equally effective for weed control, reports Alabama Cooperative Extension Service regional agent Mallory Kelley. Applied in sufficiently thick layers, all mulches discourage weeds by blocking the sunlight they need to survive.
A 2008 "Consumer Reports" website test compared the degree of fading in red cedar mulch with that in two brands of rubber mulch. All three experienced partial exposure to the elements for 32 weeks. Test results showed slight fading of the cedar and one brand of rubber mulch. The second rubber mulch had noticeable fading. These results indicate that color integrity among rubber mulches varies from variety to variety, just as it does among wood mulches.
Weight is one of mulch's most important properties. Lightweight mulches are susceptible to flooding and wind loss. "Consumer Reports" tested its red cedar and rubber mulches resistance to a leaf blower on its highest setting. With the blower standing between 2 and 3 feet from the mulches, the cedar mulch blew away while the rubber mulches remained in place. The cedar mulch also floated way when flooded with a hose, while the rubber mulches did not.
The Washington State University Extension supports Consumer Reports' findings that rubber mulch is a more significant fire hazard than wood mulch. In the tests, a lit cigarette ignited all three mulches. Extinguishing the rubber mulch, however, proved far more difficult than putting out the cedar fire.
Elevated zinc soil levels slow the growth rate of some plants, cautions agronomist M.Ray Tucker of the North Carolina Department of Agriculture. The tires producing rubber mulch contain at least 1 1/2 percent zinc. Rubber mulch on acidic (pH higher than 7.0) soil water may leach zinc when wet. Organic wood mulches, however, release non-toxic nutrients into the soil as they decay.
When Consumer Reports published their mulch test results in 2009, they estimated the average cost of wood mulch at a $1.50 per square foot. The two tested brands of rubber mulch were $13.75 and $15.00 per square foot. Although the price of rubber mulch may decrease as its market share increases, it requires a significantly higher outlay than wood mulch. Wood mulch's decay rate, however, means regular--sometimes annual--replacement and an increased cost over time.