The Q&A Archives: Soil Contaminants

Question: I've just been moved to a new garden. In addition to the soil containing a lot of clay, it also contains pieces of asphalt churned in with the soil. Will the asphalt pieces cause a problems in growing certain vegetables?

Answer: Asphalt is a petroleum product that has the potential to leach nasty chemicals as it breaks down in the soil. Some of these chemicals can inhibit root growth and make plants grow in unusual ways. I'd be especially concerned about consuming root vegetables such as carrots, radishes, turnips, and leafy crops (lettuce, collards, etc.) grown in such soil. While it sounds like a lot of work, I'd remove the asphalt pieces with a sieve before planting vegetables. Build a wooden frame and staple 1/4-1/2" hardware cloth to one side, and sift away! This will help break up clay clods as well as remove asphalt. If this is a community garden, your site coordinator can tell you where to safely dispose of it. Your Solid Waste District can also offer advice.Good Luck!

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