Hi, katkni. I built a fairly large cold frame some years ago and use it regularly. It's southfacing with three roughly 30 x 35 inch plexiglass panes, the middle one fitted out with a heat-activated opener. I'll be overwintering 15 or so small clematis that I rooted from cuttings (sinking them into the ground, pots and all) plus assorted perennials I didn't get around to planting--some delphiniums and ruellia (wild petunia) and a few biennial foxgloves. I also found it useful this past week when frost was threatened to protect a bunch of potted hibiscus and other houseplants I wasn't ready to take inside. Just laid them on their sides.

In the winter I cover whatever plants are in the frame with leaves, and cover the whole thing with a white sheet and (hopefully with snow cover) as many evergreen boughs as needed to keep it from warming up.

I recommend cold frames, for sure. Gary

How did you do the heat-activated opener? I've been busy cleaning up and gathering seeds this fall, and haven't had time to get together the materials to do this yet.