Can you do sheet mulch over frozen or semi-frozen soil? It would be nice to do it now, while there is more time, and things are not yet a sea of mud. Also, here in Colorado the ground does not freeze deeply, and most of our rain/ snow comes in March, April and May. It would be nice to have the "sponges" of organic matter ready for this.
I could, of course, use a big sheet of builder's plastic to heat the ground.