Mums root very easily from soft wood cuttings.
You may be able to divide them in the spring, but you will fors ure be able to start new plants ...if they live over the winter.
Linda c

Soft wood cuttings in the spring? If so, how large would they be by the fall (compared to, say, a new one you'd buy at the store), and would they bloom in the fall already? Don't know how fast growing they are.

MANY commercial mums are NOT hardy .... ergo .. as Linda noted ... they do NOT come back after winter ...

if you cut a piece of mum .. with two sets of leaves .... and strip the bottom set .... and put them in a glass of water ... or in damp potting media.. and cover with a baggie .... they will root relatively fast ... i am sure if you put PROPAGATING MUMS into a search engine.. you will get millions of hits ...

proper pruning of a single stalk plant ... requires that you shear it back about 3 times a season ... to create the bush we all love ... rather than a one flower stalk ... every time you do this... you can root what you cut off ... YOU SHOULD TRY THIS RIGHT NOW WITH ANY MUMS YOU HAVE.. JUST TO EXPERIMENT .... but you might not know if yours is hardy ...

many years back ... i MAIL ORDERED about 25 varieties for spring delivery ..... they were under a buck each ... YOU MIGHT WANT TO TRY THIS ... but i cant remember the name of the place ... maybe Huff's .... but they appear to be out of business ...

good luck

ken