"Overwintering Mums" by Rita Rover November 2009
If you want to try to save your garden varieties, you might try the following: After the blooms fade and new growth appears around the crown, cut off the old stems with the faded blooms. Mulch with evergreen boughs or oak leaves until next March. Timing of mulching is controversial. Some recommend mulching before the ground freezes. Others suggest waiting until the ground is frozen and then mulch. Last winter I didn’t mulch the mums in my raised bed at all and had more survivors than ever!
Keep in mind that mums are not called “garden hardies” anymore. They’re not as hardy as they used to be. I’m guessing that possible reasons might be: breeders are selecting for other qualities, perhaps making it easier for the wholesale growers to get them to market and/or there’ll be more of a demand next season if they don’t overwinter.