Cold damage is inevitable if you live anywhere that cold weather can creep in. Here in South Georgia, we love our perennials, but the first freeze can turn them into balls of straw. The first inclination is to go and trim them, but before you grab the clippers, you may be causing more harm than necessary.
The Mexican Heather we have planted in our flower beds and pictured right always takes a hard hit with freezing temperatures. Each year I try to resist the urge to clip them before spring so the bed won't look so messy.
The reality is that even though the tops of this plant are damaged beyond repair, the roots are still good and have a great shot of regenerating in the spring into healthy beautiful plants. The damaged plant, although unsightly is working to act as shelter for the roots below. If you were to remove the top growth and another freeze sets in, there's nothing to protect the roots and frost or freeze could damage it to the point it may not come back.
Evergreens that are damaged by cold
You want to hold off with any major or severe pruning of evergreens until at least mid-February. Pruning evergreens too early in the year may encourage them to put on new growth, which can be damaged by any late season or spring freezes.
So think before you clip! If you can't stand the look and have to trim, apply a good layer of leaves or straw on top of the plants to protect them from further winter injury.