Raised Bed – Materials

Q: Someone recently told me I should not plant vegetables in a raised garden made with landscape timbers. Are there any non-treated landscape timbers available?

A: There is no reason to use presently available pressure treated lumber in your garden if you don’t want to. You probably know that treated lumber was once made to be rot-resistant with chromated copper arsenate (CCA).

The chemical was phased out in 2003 – 2006. Lumber is now treated with the less-problematic alkaline copper quaternary (ACQ). Two inch by six inch framing material is easy to work with.

If you don’t want any chemicals near your garden, why not buy “plastic” lumber such as Trex(tm) or Fiberon(tm) at a home improvement store? Since this type material is not as rigid as wood you’ll need to drive two foot long pieces of one half inch steel rebar every thirty six inches along the outside of the planks to hold them in place as you fill the bed with soil.

For my raised beds, I use 5/4 x 6 pressure-treated planks used to floor a deck. The decking planks are approximately 1″x6″ in dimension: great for a raised bed. I reinforce them every 4′ with 18″ rebar driven 12″ into the ground.

You could also use untreated 2″x6″ or 2″x8″ lumber and allow it to decompose over time. My guess is that it will last at least three years and it shouldn’t be too hard to replace when it rots.

Treated Wood – Safety of ACQ

raised bed