Do you have a tree that is displaying fall color right now? Although it may be beautiful, this may be a sign of health issues. In our area, most trees do not begin to change colors for the season until October. A branch or two here and there or some yellow leaves in the canopy are not cause for alarm, but if the majority of your tree is changing color now, it may be a cry for help.
Trees that change color early are exhibiting a plant response to some kind of environmental stress. The first step to helping your tree is to identify the problem. Begin by considering any recent changes to the tree’s growing space. Has there been any soil disturbance such as construction? Do you know of any other recent major disturbances? Next, inspect the base of the tree. Do you see any visible damage from animals or machinery? Is there a ‘girdling root’ encircling the trunk and strangling the root system? Finally, inspect the canopy of the tree for any clues. Does the tree have unusually small or deformed leaves? Is the annual growth from last year (identifiable on the twigs) significantly less than past years?
I have most commonly observed this issue in newly planted trees, which are under transplant stress for several growing seasons. It is a tough time in a tree’s life and some added stress this time year, in the form of hot dry weather, can be the impetus for your tree’s call for help. The red maple pictured here is newly planted, in the last 2-3 years. It has substantial trunk damage, most likely from a mower or other mowing equipment. This damage has disabled a significant proportion of the trunk’s conductive tissue which has limited its ability to transfer water and nutrients. The resulting stress has caused early fall color as the tree attempts to go into dormancy prematurely this year to conserve energy.
In some cases, the damage a tree has experienced may be irreversible. Unfortunately, extensive trunk damage cannot be repaired. In many urban settings, soil compaction or poor drainage have a major impact on tree health and correcting soil issues can be quite difficult. Therefore, many times I find that the only practical way to mitigate the damage is to follow some general recommendations for boosting tree health. Any bit of help you can provide may be enough to get your tree through these tough times.
Often, the best recommendation for a tree showing signs of stress this time of year is watering. Trees need more water than you might expect. Although 90% of tree roots are located in the top 12-15 inches of soil, turfgrass (which is most often a tree’s biggest competitor) often steals the rainfall during smaller rain events. Since turfgrass has a dense root system concentrated in the upper 2-6 inches of soil, it is able to outcompete trees when the rainstorm does not thoroughly saturate the soil profile.
To effectively water a tree, the soil needs to be saturated beyond the tree’s dripline. Concentrate the watering closer to the dripline and further from the trunk on large trees. In order to achieve saturation and avoid runoff, water slowly over a long period of time. If you are using a typical garden sprinkler, I recommend allowing it to water for at least 2 hours in order to saturate the soil enough to successfully reach tree roots of a large mature tree. Smaller, younger trees may take less time. In general, you should plan to provide the equivalent of a 1-2 inch rainstorm every 2 weeks during the hot, dry part of late summer and early fall.
Another factor that can vastly improve the water holding capacity of the soil, and eliminate competition from turfgrass is mulch. If possible mulch your tree out to the dripline of the canopy. Apply mulch that is 4-6 inches deep as it will settle dramatically over the next several months. This protective layer will help retain soil moisture, reduce or eliminate weed and grass competition and, over time, will add organic matter to the soil. In addition, it may help protect your tree from future mower damage by leaving a buffer between it and the mower deck.
For more information on tree care, tree selection and tree pests, please visit the University of Illinois Extension’s Selecting Trees for your Home website at: http://extension.illinois.edu/treeselector/search.cfm. Or you can contact the Champaign County Master Gardener’s Horticulture Hotline at 217-333-7672.
Ryan Pankau is Horticulture Extension Educator with University of Illinois Extension serving Champaign, Ford, Iroquois, and Vermilion Counties.