Our 20 year old dogwood did not drop all its leaves in the fall. Many are a dried up brown now. What is this tree telling us?
Your tree is exhibiting leaf marcescence, where leaves wither and die but don’t fall off. In order for leaves to drop in the autumn, deciduous trees develop a separation layer (called the abscission zone) between leaf stalks and tree branches, so that leaves can break off without harming branches.
It is most likely that when your garden was hit early and suddenly with abnormally early freezing conditions early this past autumn, your tree had not yet finished the process of developing that separation layer, and many of the leaves died while still attached to the tree. In other words, the abscission process was stopped in its tracks, resulting in dead, crispy leaves remaining on the branches.
It’s not clear why leaf marcescence occurs – one theory holds that this helps prevent leaf buds from drying out over winter. And, as the leaves will eventually fall off and decompose come spring, this process could also be helpful for the tree, by providing a source of nutrients or acting as a mulch to prevents moisture from evaporating.
Be vigilant come spring. Watch for diseases, e.g., the dead tissues at the tips of new shoots can be a breeding ground for fungi. It is possible that you may not see flowers on the affected branches this year, although your tree may bloom as usual. The dogwood has been stressed, and may appreciate extra watering and fertilizing, to help speed its growth and make it more resistant to infections.
All the best in tending to your lovely tree. We would appreciate an update from you in the late spring on whether your dogwood bloomed as usual or whether some of the blooms were indeed affected.