Question of the Week Number 1: November 29, 2018

This unusually brilliant fall color a few years ago showed the bright red of Shumard red oaks. But while the elms quickly lost their yellow leaves, the red leaves turned brown and held well into the winter.

“Why do the leaves on my Shumard red oak not fall like leaves on other trees?”

This is an interesting phenomenon. It involves something called the “abscission layer.” That’s the tissue at the very base end of the leaf petiole (the little stem that attaches the leaf to the branch or twig).

Still with me?

The abscission layer forms as temperatures drop and days grow shorter. With some species it happens fairly quickly. Leaves are green. Weather turns cool. Leaves turn color. Leaves fall to the ground.

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In fact, with some Shumard red oaks it happens fairly quickly as well. It seems to vary from one tree to the next.

But with some Shumard red oaks the abscission layer doesn’t follow those rules. In fact, it develops very slowly. You almost get the feeling that the layer is not going to develop at all. The leaves turn brown and hang on the tree. You go out after dark to get the mail or walk the dog and the winter wind whistles through them sending a chill down your britches.

Most of the leaves of this large red oak in the Sperry landscape will rustle all winter long until they finally drop in February and March.

We Sperrys live beneath a forest of pecan trees with a few red oaks sprinkled among them. Pecans start dropping leaves about the end of July. The big massive drop happens in late October into mid-November. The red oaks keep dropping their leaves clear through the winter. Which means we never really put up our leaf blower. It has consistent employment six or seven months of the year.

So have I answered the question of why the red oaks don’t lose their leaves like other trees? Not at all. But if it helps to know that your tree isn’t acting abnormally, then I’ve accomplished my goal.

I’d invite you to Google “why Shumard red oaks don’t form an abscission layer” and see the dozens of other comments and matches. They don’t explain it, either. Some questions just defy easy answers.

Posted by Neil Sperry
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