Can I Use Treated Wood to Make Raised Vegetable Beds?

Organic Treatments

• Wood is commonly attacked by fungi, bacteria and insects and also weathered by the elements. Preservatives attempt to thwart these natural processes to make wood last longer. There are two types of treated wood: those treated with inorganic chemicals and those treated with organic chemicals. Organic chemicals include creosote and pentachlorophenol. These organic preservatives are considered unsafe and are not generally available to the public. That doesn't mean they can't end up in your garden. Railroad ties are treated with creosote, a distilled form of coal tar, and are often recycled for use in the landscape.

Inorganic Preservatives

• Inorganic preservatives include chromated copper arsenate, ammoniacal copper arsenate and acid copper chromate. CCA was the most commonly used inorganic preservative up until January 2004 when the EPA forbade its use in residential lumber. CCA-treated lumber has a greenish hue and contains arsenic that can leach into the ground or get on your skin if you come into contact with the wood. The wood was never ordered destroyed and, in fact, as of 2011, CCA is still legal to use on non-residential lumber. Alkaline copper quaternary is a newer, inorganic preservative considered safe by the EPA for use in gardens.

The Dangers

• Because lumber treated with CCA lasts so long, it is often collected from older structures and sold as scrap wood. Even on old wood, arsenic can be transferred from the wood to hands and clothing. It can also be inhaled with sawdust as you cut and drill holes for your raised bed. Arsenic can leach into the soil as well. It doesn't usually leach too far from the wood, but this is little consolation in the confined space of a raised bed. Both CCA- and ACQ-treated lumber contain copper, which can turn the wood greenish. If you aren't sure whether wood you've purchased has been treated with CCA, it is best not to use it.

Alternatives

• If you don't want to risk the chance of contamination from treated lumber, there are alternatives. Untreated cedar and redwood are strong and rot-resistant. Cinder blocks, stones or bricks are options. Synthetic wood, made from recycled plastic, can be expensive but offers the look of wood with added durability.