well i dont know about florida but here in chilly Pa the first frost will kill my 160 plants and and they will turn black (so i hear) and then i'll cut them down to a couple of inches above the tuber and then dig the tuber and store them over the winter and plant them again in the spring. i asked that question too and it was interesting to find this out. :o)

Well, if Corralitos Gardens sells dahlia plants that they take cuttings from, they must have year-round bushes. Right?

No- cuttings are taken in late winter or early spring from either tubers or pot tubers that have been started early. See the Colorado Dahlia site for info on cuttings.

If the plant is young I don't see why you can't just leave it as is, although the brown stems might not be attractive in the spring. Of course as fast as dahlias multiply you might want to divid after 1st year. Leaving stms on might be good though to know where it is so you wouldn't dig there. I have read somewhere in our zones where we have to dig each year that you cut back the foliage but don't leave it in the ground too long because water can seep thru the stems & rot the tuber. That would make it seem better to leave stems on.