Should the plant survive the cold undamaged, I prune it back in spring to encourage fuller growth. It's said that removing spent flower heads helps promote more blooms, but I rarely even do this. And some gardeners prune plants back to 4 to 6 inches above ground after the first wave of flowering. The butterfly weed will regrow and produce flowers again in a couple of months. It wouldn't hurt to fertilize in March, but I don't even fertilize this tough plant.
Butterfly weed likes sun or part sun and any well-draining soil, especially a sandy one.
It is drought-resistant, but I water when we hit long stretches without rain, such as we had this summer. Butterfly weed is a must in a butterfly garden as its nectar attracts throngs of the winged insects, and it is a larval food plant for the monarch and queen butterflies. I have been growing it and eating it for about 40 years. I was recently told it's actually a gourd. Gourd or not, I will keep eating it, for it's delicious.