I am planning to build raised beds this spring for growing vegetables. I am...
I am planning to build raised beds this spring for growing vegetables. I am reading what appears to me to be conflicting information about the toxicity of treated lumber. Pressure treated lumber or landscape timbers look like some of the most cost effective materials, but I don't want to contaminate the soil. If direct contact between the soil and treated wood is not recommended, would it be recommended to put a plastic barrier between them? Thank you for helping clarify my confusion. Josh Kelly
Scott County Minnesota raised bed gardening
Thanks Kelly, for asking this important question.
Treated lumber/wood prior to 2003 was definitely a problem. Arsenic was the issue and in 2003 the EPA banned CCA pressure treated lumber for consumer use. Pressure treated lumber manufactured for consumer use after that date does not have arsenic in it, I strongly recommend that you ask your lumber company about the lumber you are purchasing.
We've had quite a few questions similar to yours. Here is an answer from another AaE contributor from early 2013:
Vegetables, and especially root crops, should be planted at least 12 inches from CCA treated lumber. Thoroughly wash all vegetables grown near treated lumber. Plant tissue concentrations of these metals are highest in roots, especially near the root's surface. If you have a wooden structure in your landscape built between 1970 and 2004 it is likely that CCA treated lumber was used. To find out if you have CCA treated wood in your landscape there are kits that can be purchased from several sources (e.g.http://www.safe2play.org/testkit.html). Pieces of lumber that bear codes like CBA-A or CA-B which indicate they were treated with a Copper Azole-based material. Copper is the primary decay-preventing chemical in all of these treatments. I am unable to find a paper that lined CBA-A or CA-B wood beds with plastic. Micronized copper quat (MCQ) is the only wood preservative certified not to release copper. One drawback to using lumber containing copper is rapid corrosion of fasteners (screws, nails and bolts) and connectors (corner braces). For this reason it is essential to use hot dipped galvanized fasteners and stainless steel or copper corner braces for raised beds. I could not find any papers that lined MCQ products with plastic.
Naturally rot-resistant lumber, such as redwood or cedar, may be used.
Thanks for the quick response. That helps a lot.