As I look out on the many trees and shrubs in my landscape, I can’t help but take notice of how many of them continue to retain their foliage. Even a couple of my maple trees still have green leaves, but also yellow ones, that are holding fast to the branches. Literally all of my hydrangeas, ninebarks and weigelas are filled with their abundant, yet dried, brown foliage.
There are some key similarities between this year and the fall of 2018 that pertain to these early cold snaps we’re getting and how they affect our landscape plants. Whether or not your deciduous tree leaves turn brilliant colors at summer’s end, their complex mechanism to drop those leaves in autumn is truly amazing.
So why didn’t my tree lose its leaves, you ask? There are a few possible explanations for why a tree didn’t lose its leaves, and both involve the weather. Some trees are more prone to leave their foliage attached than others, which is referred to as marcescence. Marcescence is the retention of dead plant organs that normally are shed, and marcescence is most obvious in deciduous trees that retain leaves through the winter.
Unlike a typical deciduous leaf, a marcescent leaf doesn’t develop an abscission zone, an area at the base of the petiole containing a separation layer (thin-walled cells that break readily, allowing leaf drop) and, on the twig side, a protective layer of corky cells. Many oak tree species retain their leaves through marcescence, but drop those leaves when the new season’s leaves develop. But for those trees and other deciduous plants who retain their leaves when they typically would drop, the causes could be due to atypical weather changes.
For more information go to: https://hgic.clemson.edu/winter-leaf-marcescence.
And this year’s early cold, as with the fall of 2018, could well be the reason we are seeing so many trees and shrubs holding tight to their brown but tenacious foliage. The plant wasn’t able to form the abscission layer, thus allowing the leaves to remain attached through the winter.
On the upside, if you listen closely, you can hear those noisy, rattling leaves on a cold and windy winter day.
Donna Tatting is a Chisago County Master Gardener.