Mine are in pots and I have a few in the ground. The pots stay outside. I have both Foxtail and regular Asparagus fern. They sure don't mind the cold. But like you say, during a hard freeze, they will die back and come back every spring. Since they are so prickly and leaves get stuck in it and around it, I take those dormant times and clean up the bed so it has a happy clean home to wake up to.
