Typically, we get calls asking about brown leaves on trees in September, but here we are in early August and we are starting to see trees begin to drop some of their leaves. Browning leaves on our trees this time of year is usually a sign that your tree is under stress, and with not much rain recently and temperatures approaching 100 degrees for longer that we like to remember, I think we know what is causing the stress. Here’s a couple of reasons we’re starting to see browning leaves.

This first up is something called environmental leaf scorch. You will typically start to see leaf scorch on trees when you notice the edges of the leaves turning brown. They start to turn brown at the edges because the edges are the furthest away from the veins on the leaves making it difficult for the leaf to push scarce water resources out to those edges.

A contributing factor to leaf scorch can be the type of tree and where that tree is located. For example, dogwoods are primarily an understory tree. This means that dogwoods do best when they are planted under the canopy of another larger tree. The shade helps them survive the warm dry season. But sometimes dogwoods have been planted out in the open without any source of shade. When this happens, you will almost always experience leaf scorch on your dogwood tree. Dogwoods planted on the west side of the house can also experience more leaf scorch due to little protection from that cooking afternoon August sun. This would also be true of dogwoods that are planted close to the home, sidewalk, or driveway since they not only get reflected sun, but their roots are somewhat restricted when planted in these locations.

It’s also possible that your tree’s roots may have been damaged during the winter from under-watering. While it’s not something that every gardener does, your trees and shrubs need water during the winter too. Even though they may have lost all their leaves and appear somewhat dormant, they are still alive and have water requirements that need to be met. Because of that, it’s a good idea to give them a good soaking at least once a month throughout the winter by watering the root zone. For most trees, the root zone extends out at least to the edge of the tree canopy.

Another thing that can happen is that our trees can start dropping leaves when under stress. This is another defense mechanism against the heat and lack of water. They are dropping their leaves because they can’t keep up with providing nourishment to the existing leaves, so they drop some leaves to better care for the ones that remain.

Typically, leaf scorch or pre-mature leaf drop are not cause for concern, because at this point in the year, most trees have already stored up enough energy for the winter and are going to begin dropping their leaves anyway in the not too distant future. If you have questions about a specific tree, take a photo and email it to us. We’ll take a look. Good luck.

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