University of Maryland Extension

Materials for Building Raised Beds

Answers to common questions about the safety of treated wood and other materials in vegetable gardens

 raised bed vegetable garden made of wood

What are some ways to preserve wood that will be used for a raised bed vegetable garden?

There are several options:

  • Paint the wood with exterior latex paint to minimize soil contact with treated wood (Source: Oregon State Extension)

  • Treat the wood with a semi-transparent oil-based stain (Source: USDA Forest Products Lab)

  • Apply a heavy plastic liner between the treated wood frame and your garden soil, allowing for soil drainage (Source: Iowa State University, Mass. Dept. of Environmental Protection)

  • Build your raised bed with a decay-resistant type of wood, such as cedar, black cherry, oak (bur, chestnut, post, white), black locust, Osage orange, or redwood. (Source: USDA Forest Products Lab)

  • Use a non-wood material such as stones, concrete blocks, bricks, or synthetic lumber.

Should I be concerned about arsenic or other chemicals in pressure-treated wood used in raised beds?

An older type of wood preservative called Chromated Copper Arsenate (CCA) contained arsenic, copper, and chromium. CCA treated wood is no longer available for residential use as of 2004. 

Alkaline Copper Quaternary (ACQ) is currently the most widely available type of wood preservative for residential use. It does not contain arsenic, but it does contain copper. It is considered to be low in toxicity. For information on the health risks associated with ACQ-treated wood, see the National Pesticide Information Center ACQ information page.

Avoid using older types of wood treatments such as CCA, creosote, and Penta-treated lumber. If you have concerns about using ACQ-treated wood for raised beds, paint or stain the wood, use a heavy plastic liner between the wood and your soil, or use a non-wood building material (e.g., stones, bricks). See Additional Resources below. 

Is it safe to use cement blocks to build a raised garden to grow vegetables?

Cement block, cinder block and concrete block, all are made with cement and fine aggregates such as sand or small stones. Fly ash is also often included. Fly ash is a byproduct of burning coal and so contains heavy metals and other hazardous waste. Labels do not give specific information on exactly what aggregate is used in the manufacture of the block. There is also little research data on this topic. Ultimately, this becomes a personal choice based on your comfort level. If you plan to use block as a raised bed material -- and many people do – and you are concerned about potential risks, you could seal the blocks with polymer paint. Or you can choose to use another material.

Additional Resources

Compiled by Christa Carignan; Reviewed by Jon Traunfeld, UME Home & Garden, 1/2018

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