Never try rooting or any other form of propagating in the winter. There is so little cell activity in a dormant or semi-dormant plant that it will just sit there....
I have an interesting point to illustrate this. In the fall last year I had to cut down a tree; the cuttings have been lying in my garage in a tub doing nothing for about 4 months. Suddenly (and nothing about their environment has changed except of course the temperature) they are starting to want to grow. So I think I'll pot them up tomorrow!
But it's just to illustrate nothing much happens over the winter months.
