In my greenhouse I made two raised beds.. I made them out of landscape timbers. I put a timber on top of each other. so its 8 inches tall but I also used a tiller to rip up the ground under the beds.. What im worried about is treated lumber. There is a lil controversy in if its safe to eat veggies out of beds made from treated lumber.. What do you guys think? treated or non-treated? Also what type of wood is the best?