CCA-treated wood, often called pressure-treated wood, is very common, and you are right to be concerned about it affecting your garden. The three main chemicals that can leach into your soil — copper, chromium and arsenic — are probably concentrated within a few inches of the base of your fence. Studies that analyzed the chemical content of soil inside raised beds framed with CCA-treated wood found high concentrations of arsenic in soil within 2 inches of the wood and normal levels of arsenic 2 feet away. Because wood fences have more surface from which chemicals can leach and from which they can cast shade, I suggest erring on the side of caution and allowing a 3-foot buffer between your fence and your vegetables. That way, they should be safe from contamination and from excessive shade.

In 2003, consumer pressure finally forced the lumber industry to switch to less-toxic, arsenic-free treatment alternatives. For more on this issue, search our Web site for “treated wood.”