After the ground freezes, remember to add mulch for your perennials. Those that have been recently planted need mulch.
Mulch serves as an insulator. It keeps the soil uniformly cold. This insulation prevents the soil from shifting during alternating freezing and thawing. That shifting can damage exposed roots.
Choose a loose mulch like composted leaves, straw, or evergreen. Put 3 to 4 inches of mulch around each plant. Be cautious to not mulch the crown.