17 June 2009
In The Garden With the Fluvanna Master Gardeners
By Irene C. Burke - Fluvanna Master Gardener
Fluvanna County Extension Office: 434.591.1950
Since 1978, research on the environmental impact of ground rubber from recycled tires, shows that the safest application is a blended asphalt product for road construction and resurfacing, which according to the EPA is the "largest single market for ground rubber." Rubber crumb is for highways not your garden.
But why are rubber mulches touted as the solution to annual mulching problems? What are rubber mulches? Do they work and if so, under what conditions? What do you expect from rubber mulch? Are you looking for weed suppression, for an organic enhancement to the soil? Do you want turf replacement, a permanent substitute for organic mulch?
The tire manufacturing process, as well as the rubber crumbing process involves chemicals wed rather not have in our gardens. The chemicals picked up from road contact add more elements to the mix. Are you sure you want this around your peas and carrots, daisies and dahlias?
Rubber crumb is said to reduce soil compaction on athletic fields and golf greens. This may be a good thing for fields with no potential for runoff, but that is often not the case for golf courses.
Crumb or shredded mulch does decompose. It is not permanent. Microbes including bacteria and fungi break down rubber. As the rubber degrades it leaches harmful chemicals into soil and into surface and groundwater, which accumulate and disperse to animals and plants---you, our gardens and me.
As with many slowly decomposing mulches, weed suppression is temporary. Airborne weed seeds make their way to the soil-packed spaces between the rubber crumbs; from them sprout unwelcome vegetation. Only the tiniest amount of soil is needed, witness the hairline cracks in pavement filled with the days wild blades.
In a January 2007 report to the California Integrated Waste Management Board, on the Evaluation of Health Effects of Recycled Waste Tires in Playground and Track Products wood chips were found to do a better job of preventing head injury than rubber mulch. Use wood chips under the kids swings not rubber nuggets.
A 2004 investigation of mulch ignition by Brewer and Steward at Ohio SU Extension found that "ground rubber, had flames within a minute and were a struggle to extinguish." No smoking in your rubber-mulched garden or on your top-dressed turf! Rubber crumb is more susceptible to spontaneous combustion than any other kind of organic mulch.
Appearance and odor
Regardless of color, rubber mulch just doesnt look like the organic equivalent. Especially in the hot sun, an unmistakable oil stink wafts from the surface, which signals the release of harmful chemicals. Id rather inhale the fragrance of tomato leaves and lavender.
Rubber mulch is toxic, temporary, flammable and an ineffective weed suppressor. It adds nothing beneficial to the soil, needs annual renewal like any other mulch, and smells terrible.
Tip of the Week
For potting prep, use a brass brush or brass scouring pad to thoroughly remove salts and other deposits, then soak the clean clay pots in fresh water for several hours.