As recyclers, we gardeners would love to turn those tires into potato towers, planting pots, and enclosures for our raised beds.
And why not use shredded tires as mulch?
It’s so tempting, but research suggests that you’ll contaminate your soil.
Several studies show that microbes break down the rubber over time. These resulting compounds leach into your soil, and then into your food and flower crops. Leachates include aluminum, cadmium, chromium, plus rubber plasticizers, softeners, and accelerators used in the vulcanization process. When tires are in contact with soil, especially acidic soil, zinc can leach at levels that are phytotoxic (poisonous to plants).
As gardeners and landscapers, it’s best to avoid the risk of leachates in your soil and food. The leachate rate may be low and more studies are needed, but these reclaimed materials are safer: recycled concrete, untreated cedar or redwood, stone, and large black plastic nursery pots.
–info from Alison Draper, PhD. Director of the science center at Trinity College in Hartford, Connecticut and researcher on environmental effects of tire rubber published in Organic Gardening magazine Oct-Nov 2010 p. 54.