Tires have posed a tough problem for recyclers for years. They seem to last forever. And who would want old tires anyway?
Some Georgia blueberry growers and researchers have found a way to use tires that may surprise you.
"We're just entering our second year of this research using tire chips as a mulch," said Gerard Krewer, a horticulturist with the University of Georgia Extension Service.
Krewer, county extension agents and UGA researchers saw a real need for a cost-effective mulch, particularly on blueberry and Christmas tree farms. Mulches help control weeds and keep the soil cool and moist.
Most landfills won't accept used tires, and communities were looking for a way to use or dispose of the tires. Krewer and his colleagues put the needs together and started studying how the tires would work as a mulch.
"They've been performing about the same as a standard mulch -- pine bark - - which was what we were hoping for," he said.
All tires are made of vulcanized rubber. The vulcanization process makes tires more durable. But it also adds zinc. Plants need a little zinc to grow normally, but very high levels can be toxic.
Tests that mixed tire chips with soil in potted plants focused on whether, and how much, the zinc affected the plants. Krewer said his field studies show slightly higher zinc levels in the soil, but no significant increase in the plant.
"So far, we're very pleased with the results," he said.
The new mulch costs about three times as much as the pine bark nuggets, which run about a penny a pound, he said. Tire nuggets sell for about the same cost per pound, but it takes more of them, since they're heavier.
But tire chips last nearly forever. "They won't need replacing in four years like the pine bark," Krewer said.
The tire chips on top of the mulched area may become brittle over time, but that shouldn't affect their longevity or mulching ability.
For slightly more money (six to eight cents per pound), a higher grade of tire mulch called crumb rubber provides a more attractive look. Processors remove the metal cables. That changes the look from metal-studded rubber to black lava rocks.
Krewer said he's seen very little effect of the tire chips on soil. During the first year of his study, he found higher levels of zinc and iron in soil under the mulch. The excess iron came from rusting metal belts in the tire chips.
Other extension and research engineers are working on more ways to use waste tires. They can help improve drainage in wet areas and prevent erosion along waterways, including on the edges of drainage ditches.
"We're all hoping tire chips will prove useful in commercial settings," Krewer said. The Extension Service doesn't recommend using tire chips as mulch yet. But the nod could come in three to five years.
"The studies are continuing," he said. "We're all still looking at how beneficial and safe this material is as a mulch. So far, the results are quite positive."
(Jeff Jackson is a professor of wildlife management in the D.B. Warnell School of Forest Resources of the University of Georgia.)