Answer: There are a number of treated landscaping materials on the market, and you're wise to be selective when building for a food garden. Stay far away from any timbers treated with creosote. They last forever, but can leach petroleum products into the soil.
There are two sides to the story concerning the safety of pressure-treated wood in gardens. One says they are safe, citing studies showing little or no leaching of heavy metal compounds for years. The other side has it's own studies and says toxins do leach into soils and reach dangerous levels. So, I err on the cautious side and recommend gardeners not use pressure-treated wood, especially for food plants, or if you have small children. Try cedar, redwood, hemlock, plastic wood or cement blocks as alternatives.
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