It's February in Detroit, MI USA and both my compost pile (three, actually) and my soil are still frozen. Nonetheless, it has been my habit to mulch heavily in the fall, dig this in as the weather warms and apply fresh compost (or other mulch, if I am short on compost) as soon as all the seeds have shown themselves. During the growing season, I try to keep a 2-4" layer of mulch at all times. To conserve water, I use a weep irrigation system (Tyvek tubing) and bury it beneath the mulch.