We love our trees, and we should. They take in carbon dioxide and in return release oxygen into the atmosphere. They essentially help provide us with the air we breathe.

In the fall, the leaves on our deciduous trees turn beautiful colors and the drop to the ground. This is all part of nature’s plan to put nutrients and organic matter back into the soil. It’s kind of a self-sustaining system that works really well.

However, many homeowners with a lot of trees endure leaf season with a certain amount of dread since they know their weekends are going to be occupied with leaf duty for a while. Previously we’ve talked about mowing the leaves with a mulching mower to help keep those nutrients and organic matter in your yard.

However, sometimes this process can be extended because not all leaves fall at the same time. Some trees seem to drop their leaves all at once while others hang on for a while. Let’s talk about that process and what’s going on.

To help understand the process of leaf drop, we need to talk about the abscission zone. The abscission zone is located at the base of the leaf, near the stem. To the naked eye, we don’t see anything different about that part of the leaf, but in reality, they are fibreless cells that are smaller than surrounding cells.

As the number of daylight hours decrease daily in the fall, a variety of chemical changes happen in this zone. The first layer of cells in this zone is known as the separation layer. The changing chemistry causes this layer to get weak, letting the weight of the leaf, sometimes encouraged by a breeze or rain, to cause the leaf to fall from the tree,

The second layer is known as the protective layer which helps protect the fresh wound to the tree where the leaf used to be attached. If you look at these “leaf-scars” you can sometimes see small dots. These show you the ends of the veins that previously carried nutrients to the living leaf.

Last year it seems like this was a bigger issue than this year, but an early freeze can disrupt this process. When we get a freeze early in the season, many of the leaves haven’t worked their way through this process and are essentially “flash frozen” in place. We call these leaves, “marcescent” leaves as they are ready to drop but remain attached. Marcescent leaves that make it through the winter will get pushed off by new growth in the spring.

On top of all this, you can factor in different varieties of trees tending to drop their leaves at differing times so some of us are done with leaves for the season while others still have leaves to clean up. Either way, we still love our trees.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org.