As of January 2004 it is illegal to use CCA. The product has been replaced with ACQ (Alkaline Copper Quat) and CBA-A (Copper Azole). Neither of these have arsenic in them. They cost more though and the content in the lumber you buy is based on the likelihood of them coming in contact with the soil, i.e. 5/4 boards for decking have much less than the 4x4 posts that go in the ground. These metals can become toxic if levels become too high though, if you are putting down a deck, let it dry first and then coat it with an oil based stain. Make sure you use corrosion resistant nails or screws when you put these together. As a professional I use only pressure treated compatible screws (sometimes nails are used to temporarily fasten in place but the screws are what hold things together). Alternatively there are Borate treated lumber products disodium octaborate tetrahydrate (DOT) but these can leach out more rapidly and require re-treatment. Hope this helps a bit Al

One idea is to get rid of the wet. If you are going to put 18 inches of dirt in there to raise the beds you must have access to some heavy equipment that you can use to dig a trench and install a French Drain around your greenhouse. ""There is cedar available locally. I'm afraid it will still rot here."" It may not rot as fast if you build the opposite of an oasis, an artificial dryer area. Get creative by using gutters at the bottom of your hoophouse leading to a sump, place your foundation wood on a gravel filled drain (with ties down a few feet into the ground below the drain every few feet). You mention a lot of wet and a dry season, dig a big hole! Here is a link that might be useful: French Drain (um sometimes this link re-directs to a septic tank)

Well Merryberry, I went the easy way out here and bought a galvanized steel trash can with lid for $22.00 at Home Depot. I am thinking that I can drill it full of holes on the bottom, top, and sides and then bury a foot or two into the ground. Nice tight fitting lid should keep those buggers out while the holes will let in air and moisturure (and earthworms at ground level). I am considering pushing the lid down in a concave manner so that what little rain we get in S TX will filter into the compost. One last thing- why not set it immediately adjacent to my tomato cage so that the compost will boost my tomato production? (I have seen sketches of a wire compost bin surrounded by tomato cages so that the nutrients could leach into the ground and feed the tomatoes) That may be a good idea for those of you who are fortunate enough to have the room to do it. I have already made the choice to cover most of my yard with fruit trees.

I don't totally understand your design. You have a layer of wood not in contact with the soil? Why do you need this layer if it's not containing soil? There is absolutely no problem using PT wood to build raised beds. The PT wood these days is treated with a copper based preservative and not the arsenic based compounds used several years ago. Even then, it was shown in several studies that the arsenic hardly traveled away from the wood. Other studies have shown that crops planted in arsenic-containing soil did not contain arsenic in their fruit. So crops like tomatoes were fine. Leafy vegetables absorbed the arsenic but not in huge quantities. Copper doesn't have the toxicity of arsenic so you are absolutely fine. I'm guessing that too much copper in the soil would lead to some noticeable problems with your plants so you would know if copper was leaching into the soil. If you are building some large raised beds, it's pretty much a guarantee that there will be no copper contamination beyond a certain distance from the wood and that distance would be very short (a few inches at most).