Is Weather Treated Wood Really Dangerous for Use in Raised Beds?

New Lumber Treatments

• Lumber treated during or after 2004 is significantly different from the treated lumber that preceded it. Alkaline copper quat (ACQ) is the most common chemical treatment used today. Other chemicals such as borates, copper azole, cyproconazole and propiconazole are used to protect lumber from wood destroying insects and fungus. These chemicals do not contain arsenic and are considered safer alternatives to CCA.

Fear of CCA

• Copper and arsenic are both naturally occurring elements found in the soil. It is often found in trace amounts in animals and plants. Problems arise, however, when too much copper or arsenic accumulates inside a living thing. As CCA-treated lumber broke down, it was feared that the chemical compound would separate into its constituent elements and leach into the soil to be taken up in great quantities by garden vegetables. Because of the overwhelming public concern, CCA usage was discontinued for residential use beginning Jan. 1, 2004.

Acidic Soils May Release Arsenic

• Acidic conditions tend to increase the loss of arsenic to the environment. Leafy vegetables such as lettuce and spinach tend to move arsenic to their leaves. Root vegetables pose the largest risk to human health, since the roots are exposed to the highest levels of arsenic. Peeling root vegetables seems to remove all or most of the arsenic from the vegetables. Carrots, okra, peppers, cucumbers and tomatoes grown in CCA-treated raised beds were analyzed and found to contain the same amount of arsenic as vegetables grown in beds made of non-treated lumber.

Alternatives to Treated Lumber

• Even though CCA is a thing of the past, treated lumber still uses chemical compounds such as copper which causes some concern among gardeners. Fortunately, there are now many alternatives to treated wood. Composite materials, virgin vinyl, HDPE and rubber lumber are alternative materials that can be used to build small raised beds. These alternative materials are often not as strong as lumber and should never be used for structural support.