The safety of growing vegetables in a tire garden a common concern as recycled tires have become popular planters for container gardening. Not only does the practice find a new use for old tires, but they're easy for gardeners to use since there's almost no digging involved. Gardeners can stack, arrange and paint the tires to suit their garden's layout and theme.
But as tires get older, they degrade.
Tires are banned from landfills, and disposing of them legally is expensive. When burned, the smoke from tire fires can release chemicals such as benzene, polycyclic aromatic hydrocarbons (or PAHs) and styrene. According to the National Institutes of Health, benzene is listed as a known carcinogen, and styrene and many PAHs are listed as "reasonably anticipated to be human carcinogens."
Knowing the harmful chemicals in tire smoke raises the question: Could tires used in gardens leach these chemicals into the soil?
What Happens When Tires Degrade
Used rubber tires are a highly problematic source of waste. However, rubber can be re-used in a variety of ways, and there are entire business sectors built around recycling old tires.
Just like the smoke from burning tires, as they age, rubber tires break down and release metals, zinc, and PAHs. Whether or not enough of these chemicals are released into the soil of a tire planter to cause health problems is not known.
There simply isn't enough research in this particular area.
While there is growing research showing that tire crumbs used as a material in playgrounds for springiness could pose health concerns, the EPA, thus far, reports otherwise.
Are Tire Crumbs Toxic?
According to the Environmental Protection Agency and the Centers for Disease Control, studies have not shown a significantly elevated health risk in children who use playgrounds made of tire crumbs.
This is partly because existing research has not examined the different kinds of tire crumbs used or looked at specific health risks that could be caused by exposure to artificial rubber turf.
Much like the use of tires for gardening, it's still not clear whether there are health risks associated with tire crumbs, but the research is ongoing.
Tire Gardens May Be OK Short-Term
Chemical concerns aside, for plants which need warm soil (such as carrots or potatoes), a tire provides an ideal container. Black rubber can get extremely hot, especially in direct sunlight. Not all plants can tolerate this warmth, so if you use tire planters, be aware of what each plant may or may not need in its soil.
While it seems like the jury is still out about the potential health threat of tire gardens, it's probably best to take precautions if you're going to use them to grow anything. If you do choose to grow vegetables in tires it's probably best to line them with plastic.
And try to avoid using tires as planters over multiple growing seasons, since it's still not clear how many toxins may or may not be leaching into the soil both in the tire and in the ground below.