Rubber mulch might sound as aesthetically appealing as an artificial Christmas tree, but it does have a few selling points. It can eliminate the need for annual mulching, since rubber doesn't break down as wood does; it's heavy enough to stay put; and you can use less of it to control weeds--you need about 1.5 inches of rubber mulch compared with about 3 inches of wood mulch. But when ignited by an open flame, rubber mulch burns hotter than wood mulch and the fire is harder to put out.
We tested RubberStuff Landscape mulch (left in photo; sold online and at some Home Depot stores), Dupont Garden Products Long-lasting mulch (center in photo; sold at Lowe's) and red-cedar wood mulch (right in photo). Here's how they fared:
Weed control. Rubber and wood did about equally well. No weeds grew through, though some crept up around the edges.
Staying power. We flooded all three mulches with an open hose. The wood rose up and floated off; the rubber remained. RubberStuff also claims not to blow away. When we held a leaf blower set on high 2 to 3 feet from the wood mulch, it flew all over the place. When we ran the same test of the rubber mulches, the Dupont blew around a little and RubberStuff didn't budge.
Weathering. We set up trays of the mulches on the roof of our headquarters, covered part of each, and left the rest open to the elements. After 32 weeks, the wood and the Dupont had faded slightly; the RubberStuff had not. Manufacturers indicate that the color will last more than 10 years, but our tests suggest that some fading could occur.
Flammability. We placed a burning cigarette into a tray of each of the mulches and a lighted match into a tray of each. The cigarettes did not start a fire, but the matches did. The rubber mulches burned faster and hotter, creating a more severe fire that was harder to put out than the one in the wood mulch.
The bottom line. Rubber mulch won't provide soil with organic material but will control weeds, and you don't need to replace it as often as wood. Rubber could be a sensible choice, especially around trees and perennials, and either Dupont or RubberStuff should perform fine. Dupont costs about $13.75 per cubic foot and RubberStuff about $15. Wood costs about $1.50 per cubic foot.
While our tests did find very low levels of lead in rubber mulch, the levels were comparable to or lower than levels in soil around homes. Note that rubber mulch isn't suitable for playgrounds or play areas: It might contain small pieces of steel or nylon. Its flammability also makes it a questionable choice for homes with smokers or in areas that get frequent fire-weather watches or red-flag warnings. Environmental groups and state governments are also conducting studies to determine whether chemicals in rubber mulch leach into soil.
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