Are mums hardy?
The mums we carry are hardy to zone 5 and should return every year in all but the coldest zones. Winter wet will cause more losses than the cold, typically. Planting mums in a place that drains well will help a lot, and avoid heavy think mulch—especially mulch that gets soggy or matted.
How do I pinch back mums?
As the mum begins to grow straight up, remove (or 'pinch') the center growing tip when the mum is 6-10" tall. This will cause new branches to form. Those branches can also be 'pinched' when they get some length to them, causing a full lush plant that will flower abundantly. Pinching is best accomplished before flower buds start to develop - the Fourth of July is a good approximate date to stop pinching.
Should I cut back mums after they bloom?
You can certainly remove unsightly flowers at any time. Wait to cut back foliage until it yellows or turns crispy. The new plant will come from the roots in the spring so the tops are not needed, but we prefer leave some of the main stem behind as a marker while the plant sleeps.
How often should mums be divided?
Mums do not need to be divided unless, after a few years, you notice they've begun to 'center out' (die out in the center). At that point, dividing and replanting will yield a more compact and attractive plant (and more mums!). Directions are here