B&Q chrysanthemum
 

Got some of these today but, of course, no mention of the variety.

http://i34.tinypic.com/42vjo.jpg

The label says they grow to 18"-24" but, as they're in flower now at a
height of about 9", do I assume they'll flower again or what? It also
says they last one season, but I thought spray chrysanths were
perennial. Maybe they'll revert to something else next year.

Assuming they survive in some form, when should I think about dividing
or propagating them? I don't have a good record in this area, having
somehow managed to kill most of last year's.

Thanks for any advice

Chrysanthemums are forced to flower as nice tight little clumps. We had them bedded out and they survived for a couple of years, usually not growing much more than 12"-15" but flowering well. I think they are weakened by the original process as they all collapsed at the same time.