I have overwintered late purchased mums in the garage, and then planted them in the spring. I left them in the pots and watered them periodically, so they didn't dry out, but that they weren't soggy either. Then, in the spring, I divided them and planted them.

My humble experience in CT was that putting them in the ground this late in the season was very iffy. Most of them died. Spring planted mums overwintered fine...I suppose if you mulched the living daylights out of them and made sure that they were in well draining places, you could make a go of it, but I just found it safer/easier to shove the pots on racks in the garage, in very cold situations, they went next to the house side, rather then the outside wall....

I occasionally pick up a discounted mum if there's new growth at the base - either to overwinter in a cool spot indoors or plant out. A minority of fall-purchased hybrid mums will dependably overwinter here in any case, but the odds of survival decrease if new basal shoots are absent.

sheesh...I just went to Lowe's and found lots of nice healthy ones for 25 cents....it's worth a try. Cover them with straw or pine boughs to mulch them and protect their crowns once the ground freezes, or store in the garage or other cool place for the winter, and plant in the spring, using Eric's suggestion of looking for ones with strong basal shoots below the current foliage.