can the chemicals in pressure treated lumber leach into the soil in a raised bed made from it, and hence enter the vegetables grown in that bed? In other words is treated lumber anathema to an organic raised bed garden?
CCA - chromated copper arsenate is the main chemical used in the pressure treatment process. Many gardeners won't use it because of possible leaching, then there are some who believe the leaching doesn't spread more than a few inches away from the wood. Some of the warnings I have read include..... Pressure treated wood is not recommended for creating compost bins. Also, since the chemicals are pesticides you should use the same precautions you would with potentially hazardous materials...wear gloves, long sleeves, eye protection and a dust mask when working with it. Wash yourself and clothes after working with it. Clean up every speck of saw dust, bag it and put in the trash. You can paint or stain it to protect bare skin when you are working in the raised bed or if there are children who might sit on it, etc. It is pretty confusing, you never know who is paying for the studies being done on the wood, soil and vegies. But I don't think I would use it. There is a newer preservative being used called ACQ-alkaline copper quat....less harmful than CCA. It is also a bit more expensive than CCA treated wood.
I just went through pondering this question myself so I read a LOT of stuff about it and talked to people at nurseries and the Home Depot. The gist of what I learned is this: The good news is the CCA was deemed not usable for residential applications by the EPA in 2006. But it is still used in certain commercial and/or marine applications. Still if you were to buy from a regular lumber yard, you probably wouldn't come across CCA and that seems to be the worst of the worst. But in reading about the newer versions, the ACQ that Toni mentioned and another process called CA (copper azone), there are a number of different opinions out there -- basically the research is "inconclusive" re: negative effects on veggies grown in pressure treated beds. Some sources say chemical leaching is not a problem. One article said that the amount of chemical that might leach out would "kill the veggie" before it was high enough to hurt a person. Personally I found that to be a not-very-comforting way to look at it... Other articles mentioned the higher levels of copper as potentially worrisome but still others said copper is harmless. You can google "pressure treated lumber for vegetable gardening" and sift through the material, which was actually interesting reading. I looked into using a composite material like Trex or Veranda though it is EXPENSIVE or untreated wood with a sealer. Some articles that I read suggested using a plastic liner if you decide to go with pressure treated wood (though you also have to watch out for the chemicals that may be in some plastics... see it goes on and on). In the end, I decided to just use my same old pots again this year. I will reconsider this question for next season. Good luck with your decision making process! And Welcome to GardenStew from Maryland too, by the way! Sorry if I went on and on, I just found this question to be interesting...
We used 1"x8" cedar boards for the nursery bed and the raised carrot/onion/beet bed will be made from 1"x12" cedar boards next weekend. They will have to be replaced in a few years but that's no biggy.
Cedar, that is a good idea, Toni. I will have to put that on my list of things to consider. Where do you buy your cedar boards? I haven't seen them but have only checked at the Home Depot and Lowes. Maybe I need to go to a regular lumber yard?
I got some at Home Depot, our Lowe's also has them. You might have to ask someone, there isn't a very large selection at either store. It's 'rough cut cedar' so it probably won't be in the same section as the white pine boards...at least they aren't in the stores here.
