pressure treated wood is normally NOT used for edible plantings because it can leach toxins....

I do not know if paint or sealer will be enough protection. Sorry.

As a home builder I use a significant quantity of PT wood. New chemical formulations have supposedly reduced the toxicity and possibly the performance of the treated wood products we buy. The old PT presented health risks either from burning or breathing the saw dust, not to mention handling because of the arsenic content.

I've asked the manufacturers about the safety of using PT for vegetable gardening and have not received a very "thumb's up" response and have concluded it's probably not safe. I'll be building a raised bed garden with something other than PT.

Mark

you can try using Lifetime Wood Treatment (link below) as a non-toxic preservative on non-treated wood. I found mine at a local paint store, or you can order it online.

Will it last as long as PT? Probably not - but it might make it last long enough, especially if you are using some thicker lumber to start with.

Here is a link that might be useful: Lifetime Wood Treatment

Painting the insides is not going to prevent leaching of chemicals. It's correct that PT wood uses less toxic chemicals, but I still would not use them in raised beds. I recently made some raised beds. For one set I used untreated cedar, and for another I used Trex-type synthetic lumber. If your friend has already constructed these beds and is intent on using them, then he should at least would lay down some heavy gauge visqueen all along the interior perimeter to lessen migration of chemicals.

I lined the insides of my pressure treated raised beds with 2 layers of poly stapled to the inside.

This is a good article. The PTW now on the market is not CCA, so arsenic is not an issue. The ACQ will require the coated (usually green) screws to prevent corrosion.

Here is a link that might be useful: Does Pressure-Treated Wood Belong in Your Garden?

Good point Cowgirl. PT lumber corrodes fasteners, including Simpson hardware. Some years back they developed a zinc coated product to withstand corrosion. Codes now require that fastener product. I use approved hardware when in contact with PT on all of my projects.

Mark

I wonder if plastic 2 X 6 decking would be more suitable for raised beds. I know of a store that sells "mill ends" of short pieces by the pallet pretty cheap- most pieces are 4' long and seams could be stagered to make sturdy walls.

Since Trex, etc. is not t&g, you'd have no way to stabilize joints broken at random intervals, unless you did some cleating, tying pieces above and below joint together. You'd risk a "blow out, d.o. pressure, of course.

Mark