Hi Ellise
Once the Mums have died from a frost you can cut them to the ground and protect the area from the Winter with some Mulch, As far as Dividing them they say every 3 to 5 years in the Spring. Hope that Helps.

That's what I would do too, Ellise, but I have read that some people reckon keeping the top growth on the plant til spring protects it from frost during the winter. As with so many things there's more than one opinion.

I leave the stems in place until spring and then cut them down when I see new growth. I divide them about every 4 yrs or when they outgrow their space.