One of the most frequent questions during this season is  "Are your garden mums the winter hardy variety?"
Speaking from my years of gardening experience, I can say YES  IF you plant them before mid-September.  I have mums growing in my perennial gardens that were planted in late August two years ago.  They have had absolutely no special treatment to face the frigid January & February temperatures of 2014 & 2015 and they are doing fabulous.
Mums that are used to decorate your porch in their pots until Thanksgiving, and then popped into the ground before it freezes will not likely survive.  They need time for their roots to grow well out into their surroundings before the first frosts.