subsonicdrone

check out "citrus in the snow" and other poor mans geothermal set ups
earth insulated greenhouse, walapini, rocket mass heated greenhouse,
pushing air from the peak of the greenhouse in the summer down 12 feet to store the heat underground, same principle but less deep during spring and fall for high daytime cool nighttime temps
roll up motors for insulation to roll down at nighttime (would need to be inside greenhouse with other supports for it to roll up and down on)

I would like to build a greenhouse as well but it is at least a couple years before I could think about following through
Id like to make one with all the techniques above and more.. another design for even colder... and some cold frames etc