Trees for Tennessee Landscapes - Choosing the Right Tree
Differing shades of red, yellow, orange and purple. Autumn in full color. What triggers the color change? What color or colors do each species of trees turn? What causes the variations in color?
The factors that influence autumn leaf color are shorter day lengths, weather (primarily cooler temperatures and less moisture) and changing levels of leaf pigments. The only constant factor from year to year is the shortening day length. As days become shorter and nights grow longer, biochemical processes in the leaf initiate changing leaf color. All the other factors vary annually, making the prediction of autumn color unreliable.
"SP529 Changing Colors of Leaves," The University of Tennessee Agricultural Extension Service, SP 529-15M-3/99 R12-4910-17-001-00, http://trace.tennessee.edu/utk_agexfores/52