One of the most obvious impacts of this winter’s winter is rapidly becoming apparent in Michigan and other parts of the Midwest: winter burn on conifers. The primary symptom of winter burn is needle browning, especially on evergreen conifers in exposed locations. Needles may be damaged by extreme cold or the browning may be associated with winter desiccation as needles lose moisture during brief warm-ups. Winter burn is one of those situations that draws a lot of attention because it can look devastating; yet it often has relatively little long-term impact on plants.
The key to the lasting effects of winter damage on evergreens is the extent to which buds are damaged.
With a little practice it is relatively easy to determine the state of conifers buds. With your thumb and forefinger pull the bud scales from the top of the bud. With a good hand lens or dissecting scope you will be able to see the bud primordia. On healthy buds this will be bright green; on damaged buds the primordia with be brown or black.
I recently examined buds from Douglas-fir trees on campus that had severe needle browning this winter. In several cases, trees had severe needle browning but the buds were fine. These trees will likely put on a normal growth flush this spring and in a year or two it may be difficult to tell they were ever damaged – assuming we don’t have a repeat of this winter’s severe weather.
On some other trees, however, the buds had been killed by this winter extreme cold. This doesn’t mean these trees are dead – they may still form adventitious buds along the stems – but it will certainly set them back and will likely impact their form and symmetry.