Depends on what you're growing - dwarfs are fairly easy to greenhouse - I've kept them going thru more than a few winters in a regular hoophouse tho sometimes you have to stuff them in there. And remember, where you can't go down, you can bring down up
Nevertheless, I'm using the Bolivian walipini design for my pit greenhouse and here in Texas we have no shortage of sun, even during the winter. It'll get very warm in there during the day and only a few nights are really cold - the earth-mass will help offset that. I may use a solar heater to heat up water-tanks in there for really bad periods. Only a small fraction of glazing area will be exposed compared to the earths surface area (walls and floor) as well as the volume inside. The plants roots will be growing well below the reach of the winter chill - even tho our top-soil only freezes perhaps a few inches if that on really cold nights. Gives me a larger latitude than what I'd get in an above-ground greenhouse. The original walipini's were in the highlands of Bolivia that has similar tempuratures in their winter that we do here and they're about as low-tech as you can get. All my trees will be pruned to fit - cacao can get to 40' in the rainforests, tho plantations often prune them to around 11'. Coffee will be pruned to around 8'. Cashews around 15'. Avocado will be kept around 8 to 10'. Papaya will be composted after around 12' - you can almost grow those as annuals. You can see, even tho it's 12' wide and 45' long - it will still get tight in there really quick. Lotsa pruning to keep things happy. Anything with any cold tolerance will be planted topside. I'll dig a root-cellar to store taro corms, gingers, plumeria and others over the winter. I had lemongrass survive last winter topside - will experiment some more in hopes of having a permanent bed up there, tho a cold-frame could also be implimented too. Same with pineapples - bermed coldframes for them too. Needless to say, working at home takes on a whole new meaning when you have all this extra work to do as well.
Originally Posted by frankthetank
Nice hole Mike! I figure i'd have to get down pretty deep to raise bananas up here in the winter! SO you won't be heating that at all??? How much sunlight does that get?