I was wondering something similar, I did find this article
http://ohioline.osu.edu/hyg-fact/1000/1219.html
I have always considered hardy & garden mums to be the same, with annual mums referred to as florist mums.
At the end of the article it also states that garden mums should be considered an annual. I have lost some mums in the past few years, but some of those I think were actually florist mums & purely annual. I have 4 or 5 that have persisted about 4 years & look great each year.

Someone told me that the ones with larger leaves are florist mums and the ones with smaller leaves are the hardier, garden mums. For best results I think you need to plant them in Spring, however. But fall ones do often make it.

The huge double mums, the spiders and florist types are not really hardy up here but I have several small flowered (cushion) ones that I've wintered over outside for years. I think the distinction should be between florist and garden mums. Most of those sold potted in the fall would be hardy if they were planted out in spring.
One option is to cut back the potted ones after the first frost and bring them inside to a sunny window. That would mean using an all purpose garden spray to avoid bringing in spider mite and other beasties. If wintered inside, they could then be divided and set out in spring.

Spring seems to be the consensus. I must have gotten lucky because I bought those smallish 'colored pot' cheapies from Wal-Mart (or was it HD?) last year, and although the pinks didn't come back, the yellows are HUGE and beautiful this year. I planted them in the ground as soon as I brought them home. Only one is showing signs of deadening in the middle.

I'll make an attempt at dividing them in the early spring before they come out of dormancy, yes? Or are you actually waiting til like April?

Though the common practice is to plant mums in the spring I always plant them in the fall as have no room to overwinter them, too many other plants brought inside. :-)

Most have survived and continue to bloom, some more than ten years old. I can't bear to toss them into the compost pile so pop them in the ground. The biggest problem I have is finding space in my gardens, some are culled to make room for a differnt color or flower shape.

Bobbie

I love my mums! They still look beautiful after the last two nights of frost.

I have mixed success, usually buying in the early fall: I never see them much earlier. Mine are all the small flowered cushion ones. I've been planting them yearly but not spending much since they are iffy on return. I'd say about 30% have come back, as long as I don't plant them too late. I've bought big potted ones and tiny 88 cent ones, makes no difference in survival. The big ones bought this summer were inhaled by slugs before I could turn around and put bait out. Actually disappeared almost overnight, eaten down to tiny short twigs. They are coming up from the base but I sure won't see flowers on those anymore this year. Since there's almost nothing exposed to cold and wind above ground, maybe those will live! The little 88 cent cheapies are doing fine.

When they emerge in spring (those that live...) I nip them constantly to make them bushy.

if you see mums that you like, ask for a cutting. they root incredibly easily. and then the mother plant recovers beautifully. try asking around early may....you will have flowers in the fall from a plant that you can ask about. there are a few methods of starting the cuttings, but if you trim most of the leaves off, and cut in half the remain 2-3 larger leaves, then sick in good potting soil, and keep moist, you will get roots. florist foam (oasis) also works. you will see roots coming out the bottom of the foam, or your pot, and then you know to plant it.

I too, pinch my Mums from early spring thru July, but I use these pinching to start new plants. They are very easy to start and this keeps my supply going form year to year. About once every 5 years, I replace a lot of them with new stock/varities and colors.