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. But early cold snaps or extra-long warm spells can throw off a tree’s rhythm and prevent leaf drop. Why didn’t my tree lose its leaves this year? That’s a good question. Read on for an explanation of why your tree hasn’t lost its leaves on schedule.
Why Didn’t My Tree Lose its Leaves?
Deciduous trees lose their leaves every fall and grow new leaves each spring. Some usher out the summer with fiery fall displays as the leaves turns yellow, scarlet, orange and purple. Other leaves simply brown and fall to the ground.
Particular types of trees sometimes lose their trees at the same time. For example, once a hard frost sweeps through New England, all the ginkgo trees in the region promptly drop their fan-shaped leaves. But what if one day you look out the window and realize that it’s mid-winter and your tree hasn’t lost its leaves. The tree leaves didn’t drop in winter.
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. These include trees like oak, beech, hornbeam, and witch hazel shrubs.
To understand why leaves did not fall off a tree, it helps to know why they usually fall in the first place. It’s a complex procedure that few people truly comprehend.
As winter approaches, tree leaves stop producing chlorophyll. That exposes other colors of pigment, like reds and oranges. At that point, the branches also begin to develop their “abscission” cells. These are cells that scissor off the dying leaves and seal up the stem attachments.
But if the weather drops early in a sudden cold snap, it can kill the leaves immediately. This takes the leaf color directly from green to brown. It also prevents the development of the abscission tissue. This essentially means the leaves are not scissored off the branches but instead remain attached. Don’t worry, your tree will be fine. The leaves will fall at some point, and new leaves will grow in normally the following spring.
A second possible reason that your tree didn’t lose its leaves in fall or winter is the warming global climate. It’s the dropping temperatures in autumn and early winter that cause the leaves to slow the manufacture of chlorophyll. If temperatures stay warm well into winter, the tree never starts making abscission cells. That means that the scissor mechanism isn’t developed in the leaves. Rather than dropping with a cold snap, they simply hang on the tree until they die.
Excess nitrogen fertilizer can have the same result. The tree is so focused on growing that it fails to prepare for winter.