Propagation: Cornus controversa 'variegata' cuttings, 0 by Pistil

Pistil wrote:
Hi everyone. I need advice.
I am trying to propagate this beautiful tree by hardwood cuttings. I took them after Christmas, from a healthy specimen at a local nursery-the manager gave permission. I used some vigorous watersprouts, as the regular branches seemed to put about 1/4 inch of growth on per year, and I couldn't figure out how to do the recommended 2-3 bud cuttings. The watersprouts had about a foot between buds, so mostly I did single bud cuttings, 2-4" long. I damaged the bark a bit with a knife, dipped in rooting hormone powder, then sank them in 1:1:1 mix of potting soil:perlite:pumice, in a 6" pot. I put a plastic bag over it, and put it on my open porch (facing north) on a heating mat. Now the buds are swelling!
I think it might be time to fertilize.
It might be time to pot them on.
I think they might need some light now. My choice is to use a plastic cold frame that has an automatic opener so it will not get too hot, with or without the plastic bag, or just put it out in the yard under a tree where it would get more light, but not be protected much. I don't think I can put the heat mat out in the rain. I live in a very mild climate, so if a hard freeze should occur, I can bring them inside, but it should not get much below 32 degrees from now on (crocuses are blooming, perennials are emerging).
What do you think?