Believe it or not (and maybe you don’t believe it), but many horticulturalists believe that the recent dieback on trees and shrubs in the landscape and nursery can be at least partially explained by winter injury.
By winter injury I mean: desiccation from drying winds and exposure, extremely cold temperatures that led to freeze injury of buds and in some cases, conductive tissues.
Here is an extreme example, freeze cracks on an Eastern white cedar where it got so cold that the little free water in the inner xylem expanded into ice crystals and caused all the tissues to pop open:
It happens more often than you think. Not all of the conductive tissue is killed in the process and so often there is enough active tissue to keep the shoots, and new foliage going well into spring. Until it gets HOT and DRY. Once the plant is stressed, it has to sacrifice those damaged branches and soon we see twigs crashing, right about now:
Other deciduous trees and shrubs were also victims this winter, and the results are everywhere. Terminal buds and twigs were the most common victims of extreme temperature warfare:
On several trees, you can see where new leaves emerged but did not have enough functional conductive tissue to supply them with water and they crashed before reaching full size, or a few weeks later:
Here’s a sweet cherry in north Toronto that leafed out but then crashed violently around the third week of June. It almost resembles a really severe leaf blight disease and can be easily misdiagnosed as such:
What can we do? Hope that most trees will recover with proper pruning, fertilizing and root zone aeration and ammendments. We’ll need to remove and replant where others will not. It is going to take years to recover our urban landscapes from the ice storm of 2013 and the extreme winter of 2014.