LG --- Ive been struggling with the idea of how to heat a green house, but without using anything that will cost money.... I have been thinking about what decaying material can add.... as well as heat sinks and use of dark colors in general, angles of the roofing, etc.. A green house will not get built until I feel enough obstacles have been covered to make the structure worthwhile. Of course it will be frugal in structure.......as much "found" material as possible.
Arielle, a green house does not have to be a big expense. As far as heat, what about using Hot Bed concept? The old timers used to dig a pit 18" or so deep and fill it with horse manure. They would then set up a cold frame (technically, it's now a hot frame) over that, cover with a bit of soil, and then plant. The compost action would work through the winter, keeping the heat up, by spring the heat will have mostly dissipated, resulting in a super fertile bed, with out a lot of heat. Found materials: check out your habitat for humanity store. Lots of used windows to be had. Buy your windows, then frame to fit your windows, put a clear roof on it. Every spring, I can pick up all the windows I want at my local dump when folks are remodeling. Voila. Or you could go cattle panel route. (that's all I have) 2 panels, some framing at base, ends, and ridge, I've used a combination window at each end for doors. Upgraded to a green house tarp this year. Even without an active heat source, it will add MONTHS to your garden season. Most likely 2 months at either end. You could build your green house at least 8' wide, and put a walking path down the middle, line that with slate, or other dark stone. Instant thermal mass for heat retention. Black barrel of water = More thermal mass, as well as available water. You could even put a stock tank heater in it so if you're hit with a lot of cold, you could provide some heat at night with that. For every layer of protection you provide in comparison to bare ground, you raise the micro-climate 1.5 planting zones. For example: My zone 4 green house brings my planting zone in the green house up to 5.5. If I have a bed IN the green house covered with plastic or glass, the interior of that bed = zone 7. Of course with those added layers, there's also a bit of loss in terms of sunlight, but you get the idea. You might want to go to your local library and check out some books. Check out "The 4 Season Harvest" by Eliot Coleman.
But, I find that the green house is SO much more to me than a green house! It's a place to go in the winter to play in the dirt. It's a place to feel the sun on my face without freezing in the winter. It's a place to let the chickens dust bathe to their little heart's content in the winter. It's a place to take baby chicks out in the early spring to get their first spring greens and gut load of soil microbes.
Today and the next day and for many days after that I'm digging up bermuda grass. It's the only way I've ever been able to really get rid of it. The previous owners tried weedkiller with little success. The weedwacker helped it spread far and wide. Covering it kept it's roots moist in our dry desert allowing it to get a foot hold. Burning it made it denser then ever. But once done digging it out, the gravel will be cleared and the soil aerated from sifting out roots. Sounds like the start of a new garden to me.
Good plan. Are you planning to mulch that new garden? I'd suggest that you mulch the whole thing with cardboard or newspaper followed by leaves, wood chips, lawn clippings, and what ever mulch materials you can get your hands on. Have you viewed the Back To Eden film?