When the weather gets cold plants can desiccate due to freezing temperatures and drying winds. Broadleaf evergreens are most susceptible to this. The best way to protect them is to make sure the root ball is damp and then tuck them in at night with an old sheet or burlap sack. I do this for my Daphne odora and Clematis armandii on especially cold nights that are accompanied by heavy north winds. A small amount of protection goes a long way in saving those special plants during a cold snap.