Phillip from Hoboken, NJ writes:
I have access to salt treated lumber and I want to know if it’s safe to use in the garden. Most of it is leftover from tearing down a friend’s deck but I’ve also acquired bits and pieces over the years. I read your Square Foot Gardening post and I’d like to use it to make the sides of the beds.
Phillip, this is a common and very valid question. Many people have access to salt treated lumber, even if it’s the used type as you discuss. Much fear exists in the gardening world when it comes to growing food in beds built with salt treated lumber. The most prevalent fear involves using Copper Chromium Arsenate (CCA) treated wood. Up until late 2003, a great majority of the salt treated lumber was treated with CCA. The lumber industry changed their method of preserving wood and now uses Alkaline Copper Quat (ACQ) and other chemicals that don’t contain arsenic. Does that mean that it’s OK to use salt treated lumber in the garden?
In my opinion, no. Placing wood in contact with high quality soil that is rich in organic matter will only speed up the leaching of chemicals into the soil. If you’re planting dahlias and daffodils, plant to your heart’s delight…you’re not eating the dahlias and daffodils. But if you plan on using the raised beds for vegetable gardening, there is too great a chance of the chemicals being taken up by the plants and ingested by you. I know that I sound like a Negative Nellie so far when it comes to using salt treated lumber in the garden. BUT, I have some options for you Phillip:
- Wrap the side of the wood that is in contact with the soil with plastic. Pick up a roll of vapor barrier from the home improvement store and you’ll save yourself a lot of guesswork when it’s time to dine on your harvest.
- Plant 6″ away from the edge of the bed; a foot would be even better. The chemicals that make up the preservatives don’t move readily in the soil so 6″-12″ is a sufficient barrier. With that being said, be sure not to mix the soil when you clean up the beds in the fall. Also, this may not be practical when you are planning a conventional 4′x4′ bed as every square inch is valuable.
- Consider the volume of chemicals you could be ingesting by eating conventionally grown produce. If you currently consume organic veggies, I don’t have an argument here. But if you buy your veggies from the produce department at the local Piggly Wiggly, you’re probably going to be better off eating your veggies from your beds built out of salt treated lumber.
The long and short of whether it’s safe to use salt treated lumber in the garden is no…with exceptions. If you have the time and energy to make a few modifications before you fill the beds with soil, you can repurpose that decking into something that produces delightful food for your family. I hope to hear from other Mid-Atlantic Gardening readers about their experience using salt treated lumber in the garden. Leave me a comment below or e-mail me at firstname.lastname@example.org. Happy gardening!