Today we break with protocol and rather that answer one of your questions we are going to answer one of mine… yes, I still have questions… lots of them. Here’s the deal.

I, like many of you have noticed the leaves from our deciduous trees are not falling like they usually do each fall. In my experience, the leaves from the trees in our yard are mostly on the ground by Thanksgiving. However, this year it appears that 1/3 to 1/2 of the leaves are still up in the tree.

On my walks around the neighborhood, I discovered it is not just us, trees all over seem to be clinging to their leaves and some of the leaves that would normally be brown and down are still green. Things like this make me curious.

As most of you know, our normal first freeze is typically around November 15^th give or take. My suspicion was that this change in the leaf drop pattern might be related to that early freeze, so I decided to check with David Hillock. David is the Extension Specialist for Consumer Horticulture and the Master Gardener Program at Oklahoma State University. David confirmed the early freeze was at least one of the contributing factors for our late leaf drop and provided me with information explaining how leaf drop happens. I figured since I was curious about this, some of you might be also, so here goes.

Leaf drop is triggered in the fall by the shortening day length, frost, or even drought. All of these come together to tell the trees that it’s time to start preparing for leaf drop. These preparations involve the abscission or separation zone found at the base of the leaf’s petiole. Petiole is another word for the leaf stalk. It is the petiole that attaches the bigger part of the leaf to the tree.

Normal conditions in the fall of cooling temperatures and shorter days cause the cell wall in this zone to essentially dissolve, leaving the leaves barely attached and ready to drop. While this is process is happening, a different group of cells at the base of the petiole begins to form a protective layer of cells to seal the wound after the leaf falls to the ground. Now some trees like oaks tend to be reluctant to give up all their leaves anyway, but this isn’t a normal year.

This year the early freeze left many leaves on our trees essentially “flash frozen” nipping this process in the bud so to speak leaving many “marcescent” leaves on the tree. Marcescent means that the leaves are ready to drop but remain attached.

While this is an interesting consequence to this year’s early freeze, there is no cause for concern. It does however mean that we won’t be done with our leaves until the spring when new leaf buds push those marcescent leaves off the branch and down to the ground. See you in the garden!

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. Photo: Tom Ingram