Pest Alert – Evergreen Tree and Shrub Leaf Drop
Each spring and fall I get questions about rhododendrons, magnolias, hollies, and other broadleaf evergreen plants dropping leaves. Home gardeners get concerned when they see their favorite rhododendron, magnolia, or holly losing leaves. The good news is that leaf drop is not uncommon in evergreen trees and shrubs. I call this phenomena ‘evergreen leaf drop’.
We all know that deciduous plants such as oak trees drop all of their leaves each year all at once. What people do not realize is that evergreen plants such as magnolias drop many of their leaves each year too. Generally, evergreen trees and shrubs drop their leaves a few at the time throughout the year. Sometimes though, evergreens such as magnolias will get stressed by environmental factors and dump many of their leaves all at once. To the avid gardener, this can be disconcerting.
So why do evergreen trees and shrubs sometimes drop copious amounts of leaves? Sometimes trees will drop their last year’s leaves to take advantage of an early spring. Other times, as was the case last year, trees will drop their leaves in the late summer due to a year that has been particularly wet. In wet years leaf spot fungi will infect the leaves and the plant will sense the attack and drop the leaves.
This year we had an early warm period. This sent trees into growth mode and trees started using nutrients to grow 2020’s new leaves, flowers, branches, and wood. However, if a tree is low in nitrogen it will move nitrogen from the older unproductive leaves to the new leaves and flowers. In the absence of adequate nutrients trees sometimes dump older leaves get rid of their old unproductive leaves in favor of their new leaves.
So what does this mean to the longterm health of the plant? Generally, if the tree or shrub in question has live buds at the end of the branches where the leaves are falling then the plant will recover. Look at the image to the left; the new growth looks fine. We generally recommend an annual addition of slow-release fertilizer at the rate recommended on the bag to give the tree a boost.