We have proven that it is possible to create a mild zone 8 Texas winter in Kansas with no gas heating or electricity. We trap the sun’s heat each day with over 2000 gallons of water in sealed black barrels, then release it at night to moderate the temperatures. During a hot day in March if you forget to open the doors, the water barrels have the opposite effect helping to slow runaway greenhouse warming. Temperatures normally stay 20-40 degrees warmer inside and the ground never freezes. The air temperature will still frost and hard freeze but many cold season garden crops, spinach, figs, palms, cold hardy tropicals will thrive. You can start your tomatoes in late February and plant full ground plants in April that are already setting fruit. (A 20×40 greenhouse costs 10-20k; available during off-season only)