Is treated lumber safe for building raised bed vegetable gardens?

After posting a photo of my new raised bed garden frames in last weeks “what did you do to prep this week” post, I received several emails from readers asking if I had built my frames using treated lumber and they then proceeded to inform me of the health risks involved with  the use of treated wood in my garden.

One readers email gave a dire warning to the effect that I would surly die from the first bite of produce taken from the garden if treated lumber was used to construct the frames because arsenic would leach into the surrounding soil and into my food, then kill me when I ate it…

I would like to thank you for your concern, it is appreciated and noted. And to answer the question, yes, my new raised garden bed frames were built using treated lumber but I’m now concerned about it… not even a little bit.

Years ago many folks including several national magazines and agencies suggested that it was ”possible” for small amounts of chemicals to leach into the soil from treated wood when that wood was used to build frames for a raised bed vegetable garden. The main health worry was arsenic, because treated lumber at the time contained arsenic that was used in the treating process.

According to this article from University of Missouri Extension Office:

“Pressure-treated lumber uses CCA (chromated copper arsenate) or ACA (ammoniacal copper arsenate) as a preservative. However, studies done by Texas A&M Agricultural Extension Service showed insignificant movement of these compounds into surrounding soil. Pressure-treated lumber has no proven effect on plant growth or food safety.”

But, this is all a moot point because arsenic has not been used to treat lumber for residential use (with the exception of some woods for marine purposes) since December 31 2003.

So the admittedly small risk, associated with using treated wood before that date to construct raised vegetable garden beds and frames have been further removed with the elimination of  arsenic in the treating process.

According to Becky Wern, Master Gardener with the Duvall County Agricultural Extension Service and the University of Florida:

Today’s pressure treated lumber “is safe to use around children and animals and for gardens with edibles.”

Also according to The National Gardening Association:

There\’s still a lot of controvery about using treated wood for vegetable gardens. There was a time when pressure treated lumber contained arsenic (CCA) and was not considered safe for use in raised vegetable gardens because the arsenic leached out into the soil. The newest method for treating wood is Micronized Copper Quaternary (MCQ).

It is chemically different than the old CCA treatments. It is made of tiny (micro) particles of copper. These particles are forced into the wood cells or pores during the pressure cycle. Once in, they stay in, also forming a barrier keeping in the quaternary. The leaching of chemicals out of MCQ is practically non-existent and using the treated lumber for a vegetable bed is safe because the chemicals do not leach out into the soil.

However if you’re still worried then don’t used treated wood to frame your raised vegetable gardens, it’s that simple. Or line the inside with heavy plastic (but then I’m sure some will worry about the plastic “leaching” stuff  into the soil) or line the sides with rock or some other material.

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