Q.Frost damage
How do we trim plants that have been damaged by frost?
In most cases, it's best to avoid pruning frost-damaged plants during the winter, because the cut areas could allow more frost damage to happen. Wait until after the last chance of frost in the spring, then evaluate which parts of each plant are dead and prune off the dead areas.
This article will help you with pruning in the spring:
http://osceola.ifas.ufl.edu/mg/mg_faq_12.shtml#Freeze.18
Here is more about protecting plants from future freeze damage:
http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/protecting-from-winter-damage/