The weather. What else?
Ah, El Niño, the phenomenon that brought us a winter to remember and perhaps a growing season to try to forget. Remember this past winter? How short our memories are, but if you've forgotten, it was uncharacteristically Minnesota mild. The skiers and snowmobilers were bummed but for the rest of us normal people it was almost heaven.
Sounds like it should have been almost heaven for our trees and shrubs. And yet, sometimes it is not so much how long and cold the winter is but what kind of swings in temperatures we get and how much insulating snow we can maintain. Seems like the winter was still hard on some plants. The warm temperatures, particularly in February which melted most of the minuscule snow we had, coupled with a real Minnesota March when some of our first real sub zero weather showed up may have been the right combination to do some winter damage to our trees and shrubs. Trees and shrubs may have begun to think about breaking dormancy by the end of February. If you remember, during the first week to ten days in March, the swamps froze for the first time allowing loggers to get their wood out. This was not a good time for our trees and shrubs.
Winter damage will show up as top dieback whether it is the entire top or just portions of it. Or, winter injury may show up as tops that are slow to refoliate or refoliate with small and sparse leaves. The rule is to have patience. Don't be out there looking over you trees and shrubs with the pruning shears and saw in hand. WAIT! See what tomorrow brings...If the injury has simply set back the flushing of the buds, pruning out the seemingly dead portions will only result in removing vital leaf producing areas from the trees and shrubs. Plants obviously need leaves to produce food to survive. The more leaves, the better chance the trees and shrubs have to survive and grow. So, leave them alone until July. Then, if things are looking pretty dead, remove the dead portions and work with the live portions that should be flourishing by then.