Forty-four years ago when I was only 18 years old, my first job was to grow 350-6” potted “florist-quality” chrysanthemums each week, 52 weeks out of the year. The difference between a florist-quality mum and a hardy-garden mum is that the hardy mum is a cold weather perennial that should come back year after year and the florist-quality one is not. So why would anyone want the non-hardy mum? The answer is that florist-quality mums have larger and much deeper colored blossoms, which in turn makes them less hardy and more likely to freeze out during the cold winter weather in our area. If you receive one, it’s always worth the chance to plant it in the ground in August or September and hope that it might come back again next spring.
As a rule-of-thumb, if you receive or buy a mum any time other than during the fall season, it is probably not a hardy perennial. On the other hand, if you buy a mum plant from a nursery or landscape company, it will most likely be a hardy perennial. Most of the time your typical florist only deal in the florist quality mums. You can always ask the clerk but try to get a sense of whether or not he/she knows what they are talking about because so many clerks base their knowledge on what grandma taught them. And no, not all mums are perennial in our area-zone 5.
One of the problems of the “so-called” hardy perennial mum not surviving the winter is that this is one plant that really benefits from getting it into the ground as early as possible to ensure that a deep root system is established. Another problem with hardy mums (not unlike the florist quality mums) is that the breeders are working so hard at making their new varieties look better that some of the hardiness is lost in the process. This problem is felt throughout the entire plant industry and with almost every type of plant imaginable. Best advice…make sure that you really buy perennials when you want perennials and hope for the great results.