Haven't ventured as far into this as I would like, but have got an early start on greens with some cold frames I built last year. I do grow Jerusalem artichokes and dig them all winter from under a heavy leaf mulch. I've had a few nights in the high 20s here and my kale and leeks still look good. Would really like to put up a small hoophouse next year.
I have some lettuce, carrots, scallions, and basil in my greenhouse that started from seed. I have been keeping it heated with a ceramic heater with a thermostat. I think I will spend about $20 in electric to get about $10 worth of stuff. LOL