Winter greens and other winter vegetables

We're doing an winter vegetable gardening experiment in our unheated education hoop house (it used to be a 'greenhouse').

Propane costs ran up to $500/month to heat the house (and after losing all of the tropical plants after an severe freeze, without heat, a couple of years ago), it's quite appealing to run the house as a demonstration 'cold house'.

In our Piedmont South Carolina winter, we only have a few weeks with less than 10 hours of sunlight a day.  That's plenty to support winter greens to harvest, and probably to grow  -- I'm thinking we'll be able to do successive lettuce mix plantings as well as grow hardy and semi-hardy vegetables in containers.  (This house has a gravel surface so isn't conducive to ground sowing.)

West Dean, UK cold frame

We sowed various mixes of greens today, and will be doing more in the coming weeks.  There may be enough light for greens to grow through mid-December and take a rest, and then resume growing, but temperatures will be important, too.

We've got a bank of black plastic drums (recycled soft-drink syrup containers) filled with water that will be serving as a reservoir of heat, and we can always add a second layer of frost-protection with floating row covers.

If Elliot Coleman and Barbara Damrosch can grow greens in coastal Maine in unheated houses, surely we can manage to extend our growing beyond kale and collards in the Southeastern U.S. (They're tasty, of course, but lettuce, spinach, and arugula are great additions to winter salads.)