Here are a few things you can do after extreme weather conditions. Plants, especially conifers, may not show winter damage right away, so keep an eye on them as temperatures warm and plants come out of dormancy.
If an evergreen has suffered winter injury, wait until mid-spring before pruning out injured foliage. Brown foliage is most likely dead and will not green up, but buds, which are more cold hardy than foliage, will often grow and fill in areas where brown foliage was removed.
If in spring the buds have not survived, prune dead branches back to living tissue. Fertilize injured plants in early spring and water them well throughout the season. Provide appropriate protection the following winter.
Broken limbs or branches should be pruned back to the branch collar so they can heal without leaving any wood to decay. Cuts do not need to be sealed in the Northwest, but making clean cuts is important. If you have cracking in forking areas you should consider removing the more stressed out section and possibly strengthening the area around the crack with tree wrap.
Trees or shrubs that have bent under the weight of snow and ice should be propped up and supported while branches are still pliable. Hedge plants like arborvitae can be encircled with twine to prop splayed branches during the next growing season.
If a whole plant has turned black and you are unsure about the amount of life left in it you can scratch the bark with you finger nail or a knife to determine if it is still living. A viable plant will have green tissue in the cambium layer (the layer under the bark). If your plant shows no green then it is possible that it is a goner.
If your plant shows green or has healthy looking buds under the black leaves there is a very good chance of it returning in the spring.
Be sure to check plants at the base and in several parts around the structure. Remove dead plants and replace with new in spring.
Deciduous trees and shrubs can incur shoot dieback and bud death during the winter. Flower buds are more susceptible to injury than vegetative buds. A good example of this is Forsythia shrubs. Plant stems and leaf buds are hardy, but flower buds can be very susceptible to cold temperature injury.
Little can be done to protect trees and shrubs from winter dieback. Plants that are marginally hardy should be planted in sheltered locations (microclimates).
Plants in a vigorous growing condition late in the fall are most likely to suffer winter dieback, so avoid late summer pruning, fertilizing, and over watering. Plants growing in heavy clay soils should be fertilized after plants lose leaves and enter dormancy in autumn, and plants growing in sandy soils should be fertilized in spring.