Q&A: Building Raised Garden Beds With Treated Lumber

raised bed garden
Q: This spring I plan to buy treated lumber to build raised vegetable beds. Please give me a heads-up on treatment options for lumber. I know CCA is out. ACQ is supposed to be somewhat safe. 

Answer: CCA-treated wood (containing copper, chromium, and arsenic) is no longer available for residential use as of 2004. The relatively new chemical treatment ACQ (alkaline copper quaternary) is safe to use in food gardens. Some of the copper may leach over time from the lumber, but the risk to human health is considered to be low. From research we have seen, a toxic level of copper would kill the plants before the edible fruit, roots, or plants would be harvested. If you have doubts, select a different material such as brick, stone, and untreated or plastic lumber. You can forego any enclosure by mounding soil 4-6 inches above grade, leveling the top and sloping the sides.

Refer to the Home and Garden Information Center website for more information on Materials for Building Raised Beds. For further details about wood preservatives, refer to the National Pesticide Information Center’s web page, Home and Garden Use of Treated Wood.

By Ellen Nibali, Horticulturist, University of Maryland Extension Home and Garden Information Center. Ellen writes the Garden Q&A for The Baltimore Sun.

Have a plant or insect question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask an Expert.

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