I constructed a simple cold frame last fall and was very pleased to be able to harvest leaf lettuce, spinach and cilantro all winter long. I used an old double paned patio door for the glazing and I covered the whole thing with old blankets when the temps dropped into the teens. Temps in the cold frame never got much below 30 even when the outside temps dropped to 10 degrees. I was really impressed with the cilantro which really seemed to respond well to the fluctuating temperatures and was very quick to put out new leaves as I cut them to eat. BTW, I'm in the same zone as the original poster. I'm in the Shenandoah Valley of Virginia and we get a lot of sunny days most winters.

The lettuces, spinach, kale and cabbage would be fine out in a coldframe. I've been growing all 4 of those all winter long. The spinach has been doing quite nice. The warm season stuff cucumbers, tomato, squash and melons are okay in the coldframe but not until 2-4 weeks before your last frost date. If you put them out earlier than that they may get too cold at night and become stunted. Unless maybe you want to have a heated coldframe which is them called a hotbed. I use Christmas lights for extra heat. I thought about the buried cable option but I have a way of accidentally digging up things that are buried. As digdirt said coldframes/hotbeds are something that one needs to monitor every day. I use 4 different methods. The frames wide open for days above 40F, cracked open about 3 inched for days 30 to 40, cracked open 1/2 inch for days 25 to 30F and closed fully below 25F. Just harvested a bunch from this frame. :-)

the requirements will difffer depending on Genus.. 1) rooting hormone speeds up the rooting process many cuttings will root without it BUT many others will only root with a hormone. 2) depends on cutting but many will root when and only when the soil warms up. 3 it is important that the soil be damp when it freezes * if thawing occures then soil MAY need reqatering so it will be damp when it freezes again.

I plan on building a cold frame this spring, late March. I have all the materials on hand, old (30-40 yrs) 2 x 4's, and stiff plastic for the window. The 6'x12' garden plot has a fence and is full of leaves from last fall. I'll clear a 4'x 8' space and mound up the leave around the sides of the frame for some added insulation. Earlyon I plan to bring out warm water-filled 1 and 2 liter bottles before sundown to place in the frame for added warmth during the night, then late April leave them in the frame on sunny days to warm up. I have black cloth to put on the leaves around the frame to further add warmth to the area (I hope this will also speed up the leaf composting.) I have to figure out a cover for the frame for cold nights. I have extra house insulation and may devise a blanket of insulation in garbage bags glued together, hopefully well enough so that moisture cannot get in. I'll put six of the tomato plants in place permanently so that when I take the frame apart (or not) in the spring they will already be in place. The rest of the space will be for tomato transplants, lettuce, etc.I'll put a thermomoter in there first to see what the night time temps are before I put the seedlings in. Everyone need a hobby :-)