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?