Indoor Raised Bed Design

Hello Permies... we are just finishing up the structural work on our solar greenhouse and will begin building our maze of raised grow beds. Each bed is about 4x18 and they sit on top of a subterranean heating and cooling system. Each grow bed has an insulated heatsink consisting of washed stone warmed by buried pipe which circulate air beneath the stone. The south side of the building is glazed with 16mm Lexan. That said my main question is how to build the grow beds, made of rough cut lumber supported by rebar. i'd like 3-3.5ft tall, two feet of washed stone, 1-1.5 feet of potting mix, separated by weed barrier. The foreman says 2.5 feet is the most economical and stable. The primary consideration is being able to keep the rootzone from freezing, the second is ergonomics... we don't want to be bending over all day long. Thanks for any suggestions or help developing the design. Ace

I would go for a much deeper amount of potting soil. It sounds like you were planning just a foot or foot and a half? Most vegetables will grow much larger, more vigorously, and yield much higher with a larger root zone. Weeding is easy enough in raised beds that I would be more focused on creating a growing environment that is optimal for your plants. Allowing their roots to grow down through your entire raised bed, and into the native soil, is a good plan, IME. This will also allow earthworms to pass upwards through your raised beds, which will be a huge help for keeping your soil healthy.

Also be very mindful of the exact mineral and structural composition of your potting soil. Greenhouse soils are very easy to unbalance, so starting off right, with ample soil calcium and no mineral excesses, is very good for the long run. Similarly, having good soil structure with plent of air pores is important, as greenhouse soils tent to constantly compact over the years. Pumice is the best ammendment I have found for maintaining soil airspace long term.

Good to be planning well now, greenhouses are much easier to build than to maintain in a productive way. good luck!