Red maple tree with red leaves for fall. Photo by: Lenny Far.ee

The calendar flipping over to October is a reminder the annual Autumn leaf color display is on its way. The perennial question is “how will the color be this year?” Predicting the quality of the fall display requires weighing several factors that may vary over time and across the landscape. In general, Indiana started the growing season wet and is ending it dry. The good growing conditions early this year have produced abundant leaf area on many trees. As we have dried out late in the season, some trees are experiencing stress that may cause leaves to turn color and drop early, or to simply turn brown. Drought may also delay the color change by a week or more in some cases. Leaves that were attacked by insects or disease may also drop early or provide very little color. I noticed Japanese beetles seemed to be more active than normal this year, skeletonizing leaves on preferred plants like linden and Virginia creeper. Local weather patterns can also influence color intensity in a positive way. Sunny days and cool nights late in the summer and early fall can enhance the production of anthocyanin – a pigment produced in some trees that provides bright red, maroon and purple tones to the fall color palate.

This brings us to another variable: different species of trees may produce different colors, timing, and duration of fall color. Some species like sassafras, sumac, black and sweet gum, and sugar and red maple are famous for bright fall color. Some species like elms, buckeye and walnut may simply turn brown or drop early with little color display. Different individual trees may also vary due to genetic differences, growing conditions and tree health. For example, some sugar maple located in open areas or on the edge of a woodlot, receiving lots of sunlight, may regularly produce vibrant oranges and reds, while nearby sugar maple in the shade of the forest will turn a subdued yellow, lacking the sugar reserves produced by their neighbors in the sun.

Leaf color change is also the result of a very predictable process based on the longer night period as summer slips into fall. The production of green chlorophyll pigments slows and finally stops as the nights become longer and cooler, exposing the yellows and oranges of carotenoids and reds and maroons of anthocyanins. This process also starts forming a zone of separation between the leaf and branch that ultimately brings the leaves to the ground, often with the help of wind and rain.

My best answer to those asking for a fall color prediction is another set of questions: how was your weather, what species of trees do you have, and how much sunlight do they receive?

Resources:
Why Leaves Change Color, The Education Store, Purdue Extension
Why Leaves Change Color, USDA Forest Service, Northeastern Area
Fifty Trees of the Midwest App for the iPhone, The Education Store
Native Trees of the Midwest, The Education Store
Shrubs of Indiana CD: Their Identification and Uses, The Education Store
Shrubs and Woody Vines of Indiana and the Midwest: Identification, Wildlife Values and Landscaping Use, The Education Store
Trees of Indiana CD, The Education Store

Lenny Farlee, Sustaining Hardwood Extension Specialist
Purdue Department of Forestry and Natural Resources