What’s the issue?
This fall we were getting unseasonably warm temperatures throughout September and early October without our usual frosts. Normally our temperatures begin to drop in September, this combined with the reduced number of sunlight hours helps trigger a seasonal change in trees where they start to prepare for winter by downloading moisture out of the above ground tissues and adding chemicals that act as “anti-freeze” in the winter. Without any real “hard” frosts until recently along with all of the snow, some trees may fail to “harden off” before the deep freeze that can accompany an Alberta winter.
What is “Hardening Off”?
Hardening off is the process that a tree goes through to prepare for the winter. This includes the dropping of leaves, the movement of water out of tender tree tissues and other physiological processes. Missing this important step can cause water to freeze in the above ground portions of the trees which can rupture cells inside the branches and stems of trees which can result in branches failing to survive into the spring. More minor issues would include the death of tender buds that are in place to produce flowers and leaves next spring.
Will my tree be affected?
The short answer is that nobody knows, yet… Most trees have lost all or most of their leaves which is a good sign that your tree was well prepared for this sudden change in temperature, however some trees have retained their leaves later than others. In the Fall of 2022, many mountain ash trees had failed to drop leaves prior to a major temperature drop and we have seen significant die back and tree mortality related to this event through the spring and summer of 2023. Trees that have at least seen some colour change to the leaves will probably fair better than trees that are frozen with green leaves throughout the canopy. The tree in the photo above was damaged by a fall frost. Some trees with severe damage will push up suckers from the base which shows that even with ample energy, the damage to the tree canopies can be so extensive that the energy cannot be pushed back up through the damaged cells and structures.
Now What?
No decisions about whether or not to prune or remove trees should be made yet. Many trees that suffer damage can respond very slowly in the spring and leaf buds can open as late as July after a sudden hard frost. So in short, no need to be overly concerned, you will have to wait until summer to be sure what the long term outcome may be for your trees and shrubs. The good news is that most trees that have thrived in our tough climate up until this Fall are well accustomed to our rapid temperature changes.
