They need good drainage, so maybe a bit of soil preparation first. Plant the mums at the same depth as they were in their pots. Keep the plant mulched. Here is the hard part - once the cold weather arrives in Pennsylavania, cut the plant back to about 3 inches. That's right, just hack it off. Have faith (and good drainage) and you should succeed.
I might add that once the spring arrives and the plant starts to grow, you need to give it a 'haircut' to encourage branching and for more blooms.
