A few months ago I posted a caution about using old pressure-treated timbers for vegetable gardens (see my Sept. 23 posting). I now routinely get questions about alternatives to these arsenic-laden materials, especially new treated lumber. What’s in the new wood that makes it rot resistant, and is it dangerous?
Rather than arsenic, new pressure-treated lumber has copper as its active ingredient. Though it also will leach out of the wood, there is not a human health hazard associated with its uptake by plants or animals. You probably get more copper leaching into the water carried through your plumbing (assuming you have copper, and not lead, pipes).
What about plastic timbers? Though I’ve not seen any literature about leachates from plastic lumber, I’ve seen some older plastic timbers that haven’t aged well – they can warp and twist. I would avoid those made of rubber, because decomposing rubber produces leachates that are quite hazardous (see September 30 for a discussion on rubber mulches).
Of course, there are many other materials one could use to corral their veggies – concrete blocks, stone, natural wood, etc. Do you have a favorite? Post a comment to let us know!