What Happened to Fall?

It’s officially Fall and the trees seem to have gotten the message, with leaves quickly changing and the sound of leaf blowers filling the air. Pumpkins and Mums are everywhere, and cooler temperatures have us getting ready for the upcoming holidays. While the temperatures have swung wildly in the past month, it is nothing unusual for Richmond – and with dormancy right around the corner, the trees and shrubs haven’t minded too much. These crisp days are wonderful and make it easy to work outside. It’s almost been too nice.

With normal Fall weather comes rain, and it is certain this has not been a normal Fall in that sense. We are extremely dry right now in Central Virginia, with uncommon wildfires popping up and spreading quickly to the west of us. This will mean that our autumn campfires in the backyard will have to wait, and that foliage color change will likely not be as showy this year. It also means we have a greater risk of losing even more trees next year, and here is why:

In the Spring, mature trees are pushing most of their energy upward to put on new leaves and expand shoots with some root growth when soils are warm enough (but not hot). Next comes Summer, when most mature trees go into a pseudo-dormancy with less growth as they weather the heat and dry periods. Then comes Fall, when the trees have an opportunity to focus on root growth as the general flow of energy is now downward. Fall is a very important time for mature trees to prepare themselves for the dormancy of Winter and the coming push of Spring. Without enough water, trees will have a hard time doing that this year.

During the Summer, it is common for trees to have annual root death on many of the fine root hairs, and even small fibrous roots, due to higher soil temperatures and low soil moisture. This is something that trees have adapted to, and as long as woody roots do not begin to dieback, the trees can recover these losses. As soil temperatures cool and soil moisture increases in the Fall, trees are able to make up this dieback and typically develop stronger, more expansive root systems each year. Unfortunately, while soil temperatures are cooling, soil moisture is extremely low right now, which means that root growth is likely greatly reduced.

If trees are not able to make up for losses experienced this Summer, they will start off at a deficit next year. I would guarantee that losses occurred with some of the extreme heat we experienced this year. While smaller and more juvenile trees will likely be unaffected, larger and more mature trees will have to start off next Spring a little less prepared for another (likely) hot Summer. It’s not really possible to water enough to make up for the rain deficit we are experiencing, but mulching can greatly help hold what moisture is available in the soil. The most important thing to remember is that large trees will likely show stress next Spring with late leaf development and/or smaller, less healthy leaves. If a mature tree shows such symptoms next year, it would be beneficial to remember the dry Fall, and have the tree assessed before the gauntlet of Summer 2024 is upon us.