May 2, 2015

1 - Root veggies planted in tires.

Yard and Garden May 2, 2015

Q.

My friend has done some research and found concerns for root veggies planted in tires. The concern is that root vegetables may absorb chemicals from the tires. Are there other veggies that may be planted in tires that would not be affected adversely? We want to plant in healthy environments.

-A. Johnson

A.

I have often seen recommendations to grow potatoes in tire, often stacked so that as the potato plants grow up, another layer of tires and soil may be added to increase the yield in a small area. I have also heard of concerns that there are materials in the tires that are toxic or potentially toxic. Like root crops, potatoes could potentially become contaminated. I found no information about levels of these materials from tires that are necessary to cause the toxic effects, however, I did find information indicating that the amount of material leached or evolved (gaseous materials) from the rubber was greatest in crumb rubber used as mulch. Smaller the particles of rubber have a greater surface area for leaching of materials. Intact tires have much less surface area exposed to soil and therefore loose materials slowly. This was a point expressed by an author discussing the problem of toxic materials in tires used in Earthship rammed earth homes. An important point brought up by that author was that surface area exposed to sunlight which increased the rate of the loss of material from tires important factor in loss of toxic materials from the tires. His point was that there was very little tire material exposed to the external environment to leach toxic materials into a home and concluded that this was a beneficial use of old tires. His comments suggested a solution to the concerns related to tire gardens if even underground crops such as potatoes and root crops were to be grown in tires. Tires lined on the inside with plastic or treated with non-toxic water-proof paint should have very little loss of toxic materials into the soil. If the crops were not in contact with the tires and if they were washed and peeled before use, the hazard would be reduced even more.

However, as you mentioned in your question, there are many other crops that are produced above ground. Growing crops produced above the soil will further reduce the potential for concerns. Heavy metals leached from the tires are much less soluble in high pH soils typical in New Mexico and the plants will not be able to absorb these heavy metals and translocate them into the edible parts of the plant. Even in soils amended with organic matter and less alkaline should be safe for plants with above ground edible parts. Organic materials that leach from the tires are also not absorbed through plant roots and should not be a problem. Crops to consider are beans, squash, cucumbers, and other climbing plants that may be trellised to keep the fruit from contact with the tires. Tomatoes in cages, corn, and other tall plants may also be considered. This option will permit beneficial use of old tires and provide an abundance of caution to avoid the concerns about toxic materials from the tires. Protective coatings covering the tires will further reduce concerns even if the edible part of the crop comes into contact with the tire.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

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