Is it safe to use tires as raised beds in a vegetable garden?
While there was some research showing that shredded tire much temporarily added levels of zinc into the soil that were toxic to chrysanthemums, the common consensus is that and heavy metal leaching into the soil is so slow as to be negligible. A thorough washing of the tires before hand will suffice. The more pressing problem with using tires as planters, especially for potatoes, is that the rubber tires tend to heat the soil more then other types of planters, which can limit your yield or kill your plants outright. As such, it is recommended to whitewash the tires (of course using a safe, preferably natural paint or stain).