Pressure treated lumber -- O.K. for grape arbor?

      A look at pressure-treated woods, then and now, and safety factors to consider in using them. 1998.

by Professor Gene Wengert

I am about to have a grape arbor built. I have heard that pressure treated wood should not be used near the growing of food stuffs. Is this so?

First, to formulate an answer, I need to make sure that you appreciate that all pressure treated wood is not the same. Creosote will leach into the soil and poison the soil around the piece of wood. (Have you ever seen weeds around a telephone pole in the old days when we used lots of creosote?) Nowadays, the creosote treating is done so that there is less "free" creosote so it is less of a problem.

Some treatments used pentachlorophenol in LPG. This was very stable, once in the wood, and was recommended for playgrounds, etc. This treatment has fallen out of favor recently.

So, today, most pressure treated wood is treated with CCA (copper, chromium, and arsenic in the form of salts). These salts are put first into water and then pushed into the wood. There will be little residue or free salts after treatment; the salts bond with the wood to form an unsoluble mixture IF DONE CORRECTLY. You can be assured of correctness when the lumber has a stamp (ink stamp) on it for the treating (not for the grade) or has a sticker on the end. But there are some not-so-reputable treaters who try and treat wood, but are not interested in the safety of the situation. They will not have a stamp or sticker. Landscape timbers are often their product. The lumber might be advertised as "treated to refusal." (Don't waste your money on this stuff.) You can expect some excess preservative on the surface which could be disolved during the first rain storm.

There are also some newer preservatives which are even safer, if properly applied.

In all cases, however, never burn the scraps. Disposal in a landfill is legal. Avoid breathing the dust (sawdust when cutting). Wash your hands. Ask the place where you are buying the material to give you a kiss (Consumer information sheet = CIS, but pronounced "kiss.")

So, what is the "bottom line?" A study at NC State University, reported in the Sept 1974 Forest Product Journal, checked grapes that were 3 inches from CCA material after 1, 2, and 3-years. They found no evidence even suggesting take-up and translocation of wood preservative into the plants! So my answer is: Get properly treated material and then there is no risk.

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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