The Q&A Archives: Pressure-treated Lumber and Cold-frame

Question: Last fall I constructed a cold-frame out of pressure-treated lumber. After the fact I found out that this wood shouldn't be used to grow vegetables in. Is there any way in which this cold-frame can be modified to be used for vegetables?

Answer: There is conflicting evidence about whether pressure-treated lumber is acceptable for use around food crops. Some research results say its fine, that it doesn't leach toxic chemicals; other results say that it does and should not be used around food crops. As far as sealing your existing wood, I've heard of several different methods. I don't know if anyone has studied the effectiveness of them, however. Perhaps a combination would be most effective.

You can paint the wood with several coats of an appropriate sealer.

You can line the structure with heavy plastic sheeting.

You can construct a "foundation" using masonry, that would lift the cold frame so it isn't in contact with the soil.

You can cover horizontal surfaces to eliminate water absorption.

Here are a few web sites with information about pressure treated wood.

The following is a message board about using pressure treated wood in gardens. I cannot vouch for the accuracy of any of the statements, but it does provide some interesting options and opinions:

Organic Gardening magazine has been involved in the discussion of pressure-treated wood:

"How can I preserve lumber without toxic chemicals?

I do not know if this offer still stands, but Organic Gardening magazine used to offer copies of an article they published in 4/97 on the subject of pressure-treated wood, including their updated bibliography of scientific studies. Their address is: Organic Gardening, 33 E. Minor St., Emmaus, PA 18098. I believe they requested $2.00 for postage.

Other sites:

The American Wood Preservers Institute

The U.S. Environmental Protection Agency

Hope this helps.

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