Cold Frame in Zone 4-5?

I've been reading up about propagation. Most of the books talk about using cold frames for getting baby plants through the winter before setting them into the garden.
However, we get very cold winters (down to 20 below) and lots of snow where I live (right on the border of zone 5 on a hillside that flowers later than everything in town.) I can build a frame facing south, but heat isn't an option and when the snow is deep I can't get to where the frame is going to be without a lot of hassle. So I'm wondering what kinds of plants would do okay in the cold frame. I'm looking to propagate some ground cover, cranesbill geraniums, and lots of hardy dianthus.
Any tips? Is it worth doing?
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Cold frames are fantastic things to have because they extend the growing season to an extent. But:
- They require attention. They need to be opened and closed. Even on very cold days when there's no snow cover, it can get hot enough inside to hurt the plants, unless you install an automatic opener. (They don't require power, by the way).
- When there's heavy snow cover, the plants are basically in a suspended state. Unless the frames VERY overdesigned (earth & hay bales around the outside, drums of water inside), it's still going to be the same temp inside as out. This doesn't mean the frame is useless, since it provides protection from some of the physical damage winter brings (ground heaving, for instance). But, don't count on much growth, except at the very beginning and end of winter when there's less snow cover.
All in all, I'd say you should do it, but hit the library first and do some research. And, find the automatic openers before you complete your construction plans.
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You can make coldframes for nothing, out of discarded scrap wood for the sides and a double-or triple-glazed window pane for the roof. Why not try one and see?
Janet
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A coldframe will buy you 1.5 zones, but the plants have to be in the ground, if they are in pots they will freeze and die. But a coldframe is mostly used to get an early start in the spring. You know, start lettuce in march, that kind of stuff.
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