Good garden center friend Hammon Buck owns and operates a fine garden center in Rockport ME called Plants Unlimited. Hammon quite often sends out some quality gardening advice to his customer list and I wanted to share this with you as a good reminder:
"Mulching is one of the best lines of defense for perennial plants against chilling temperatures. Mulching also can prevent the repeated freezing and thawing of soil that causes plants to "heave" out of the ground.
But the trick is not to mulch too soon. Mulching needs to be done after the ground starts to freeze but before the first significant snowfall of the year. If you mulch sooner, mice and other rodents may nest in the mulch, and plants may not be completely dormant. In general, the end of November is a good time to apply mulch in Maine although if an early snowstorm is predicted, you may want to apply mulch before it hits.
You can use pine needles, straw, leaves, or shredded bark. Straw is the best mulch because it is hollow and that provides good insulation. If you use leaves, make sure they are finely chopped to prevent them from matting down. (Another good reason to wait a few more weeks before mulching is that mice and other rodents will use these loose mulches--all of which I prefer--as a winter nest if they are laid down as mulch too early).
Apply a layer at least three to four inches thick around each plant. After you've laid it down, gently pull it away from the trunks and stems to give plants room to breathe. This helps prevent disease problems. Deeper mulching may be necessary in especially cold or windy sites. "