Gardening in large containers and raised beds is the best option in many situations, such as when poor local soil conditions make it difficult to garden. Fill a few large containers with potting soil or good purchased topsoil, and you need not worry about your garden soil at all. And making use of recycled materials to make raised beds appeals to a gardener's natural fondness for self-sufficiency.
So you might think that using old automotive tires to create a tire garden makes perfect sense. After all, the size is just right for filling with your own soil mixture and growing vegetables like potatoes and tomatoes. Yet few subjects are more hotly debated among gardeners than whether or not it is safe to grow edibles in used tires. And unfortunately, there is not definitive conclusions on whether this practice environmentally sound or potentially hazardous.
Proponents of both positions are fierce in their beliefs. Advocates of tire gardens point out that disposing of old tires is a severe environmental problem, and since tire gardening repurposes them for use as garden planters, it is a good green solution.
On the other side, opponents rightly point out that tires are filled with a host of chemicals and metals, some of which are known or suspected carcinogens. They argue that it is pure foolhardiness to grow edibles near such materials.
To which the advocates counter that the toxic materials become free in the environment only when the tires are burned. They argue that because tire gardening prevents tires from being burned, it actually helps the environment.
Back and forth the argument goes, and the best that a concerned gardener can hope for is to understand both positions.
The Tire Problem
Almost 300 million tires are discarded each year in the U.S. 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 Institute of Health, benzene is listed as a known carcinogen, and styrene and many PAHs are listed as "reasonably anticipated to be human carcinogens."
Therefore, a great deal of effort has therefore gone into looking for ways to recycle waste tires in a manner that does not involve burning them. Rubber can be re-used in a variety of ways, and there are entire business sectors built around recycling old tires. For example, many types of artificial athletic turf make use of ground-up tires, and many children's playgrounds use some form of loose recycled tire "crumb" material to cushion the ground beneath play equipment. The material is resilient enough to cushion far better than sand, and it is generally more sanitary than options such as wood chips, which can cause splinters. And, 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.
There is, however, growing health concern about the use of recycled tire crumb material in children's play areas, so additional uses for old tires are always welcome.
The Case for Tire Gardens
Once such use for old tires is in raised bed gardening. The practice of using tires as garden containers creates a new use for an unwanted material, and tires are very easy for gardeners to use since there's almost no digging involved. Inventive gardeners can stack, arrange, and paint the tires to suit their garden's layout and theme.
Advocates of tire gardens argue convincingly that using tires as raised bed garden containers is a cheap and easy way to help solve a very large environmental problem. Any tire used as a garden container is a tire that isn't being burned to release toxins into the air. The practice of using tires as raised garden beds is especially popular among gardeners who champion self-sufficiency and "upcycling" of used materials as a lifestyle.
The Case Against Tire Gardens
The safety of growing vegetables in a tire garden has become a common concern as recycled tires have become popular planters. Most scientific studies thus far suggest that most of the health issues regarding tires arise when they are burned, but the list of substances that can be found in tires is enough to cause sober reflection:
Despite the fact that the EPA and Center for Disease Control have not found statistic links to health hazards from either intact tires or "crumb" products, studies are still underway and officials acknowledge that more data is required. The Mount Sinai Children's Environmental Health Center has noted that "Exposures to chemicals present in crumb rubber at very high levels, typical of animal or occupational studies, are known to cause birth defects, neurological and developmental deficits, and some can even cause cancer."
While most of the concerns about the chemicals in tires are related to the use of crumb rubber used in playground environments, some organic gardening experts argue that intact tires eventually break down and that chemicals can be absorbed by the roots of plants. In this view, even trace amounts of these chemicals can pose a notable risk over time. For this reason, many reputable organic gardening sources, among the Mother Earth News and Organic Life Magazine, caution against growing edibles in tires as a long-term practice.
The Middle Way
Gardeners who are moderately, but not fanatically, concerned about the chemicals in tires should be able to rest easy about short-term use of tires as raised containers for growing vegetables.
As they age, rubber tires do break down and release the same metals and chemicals that are known to be an immediate problem when tires are burned. However, this is an extremely slow process. The fact that tires break down so very slowly is why they pose such a notable problem in the environment, and it takes many decades for a tire to fully break down into its toxic components. Still, the process is underway to a small degree all the time.
Gardeners who are very concerned about chemicals will rest easier if they stay away from tire gardening as a practice, leaning instead on traditional raised beds built from non-treated lumber.
Chemical concerns aside, for plants that 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.
While 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 edibles. If you do choose to grow vegetables in tires, line them with plastic before planting. Try to avoid using the same tires over many growing seasons.