Most Minnesota hardy perennials tolerate unseasonable weather conditions.  Because late winter and early spring cold damage is usually superficial, affected plants recover and grow when the weather moderates. 

Although it's usually unnecessary, a light winter cover of marsh hay or evergreen boughs can be beneficial, especially when there has been little or no snow. The cover can be set aside as  the plants emerge and replaced temporarily during cold snaps.

If dry conditions persist, water as needed as soon as conditions allow.

Learn more here:

https://hortnews.extension.iastate.edu/how-protect-plants-frost-and-freeze