It may seem logical to use treated wood to build a raised bed that will last. But do you know what that wood is treated with?

Pressure treated wood is great for resisting rot, insects and holding up against the elements for years and years. Chemicals are forced into the wood that make it extremely durable, especially when there is ground contact. Chromated copper arsenate, which is 34% arsenic, has been highly effective but found to leach into the soil. Edibles grown in that soil are not safe to consume. Fortunately the EPA has banned the use of CCA for pressure treated wood for residential use. Creosote, a pesticide derived from coal tar, was an alternative chemical for treating wood but has also now been banned.

If you have existing raised beds built with old pressure treated wood, by now you can only hope that you have not consumed too much of the chemicals and that the majority has leached out from the wood. But it would be advisable to seat the wood with oil stain or sealer every couple of years. Or you could insert a liner around the perimeter to minimize contact with the garden soil.

Currently, landscape lumber is treated with copper based preservatives or borate, and most often with alkaline copper quaternary. These are in fact still toxic, but at very low levels. It is generally considered very safe to use these treated woods even for vegetable beds. However it would still be prudent to seal the wood with oil stain or sealer to prevent even minor soil contamination.

There are alternatives of course to using pressure treated wood to build raised bed gardens. You might consider a completely different, or similar, material.

• Redwood and cedar are both naturally resistant to decay without treatment or sealing

• Certain oaks are somewhat resistant to decay.

• Composite lumbers, or synthetics, are highly resistant of course and very closely resemble the look of real wood. Do note that there really has been no research into the possible effects on the soil.

• Bricks

• Galvanized corrugated sheet metal

• Boulder and rock walls can blend beautifully into your landscape.

• Retaining wall blocks are easy to work with and widely available.

If you are building a raised vegetable garden yourself, select a material that is not only easy for you to work with but that will be pleasing to you. You will be looking at it for a very long time.