The temps dropped very low over night. Now my beautiful, big ferns are dark brown. I am sure they were frozen. Is there anything to do for them? I have them inside right now, but now that winter is here, can I save them or should I just discard them?
It does appear the entire plant was effected. Frost damage can continue for a few days or even longer. I would trim away the damaged fronds and wait and see if the plant will send up any new growth.
The roots may still be alive.
Here are some articles with more information.