Sunny days, cool nights bring fall colors

By Eric BARRETT

OSU Extension educator

Now that it’s mid-October, the leaves are covering the ground. The leaf piles are getting bigger. The trees are now showing their true colors. We get lots of questions at the office relating to the conditions of trees and some questions about why they change color.

Four leaf pigments account for leaf color and it changes in the autumn: chlorophylls, carotenoids, tannins and anthocyanins.

Chlorophyll gives leaves and other plant parts their green color. Throughout the growing season in a healthy tree, chlorophyll is continuously being produced and destroyed. Even though light is necessary for the formation of chlorophyll, continued exposure of new chlorophyll to sunlight, with its damaging high-energy ultraviolet wavelengths, will destroy the pigment. Hence, if a leaf is to remain green, new chlorophyll must be made constantly.

Many of you noticed certain tree species lost leaves early this year. Many of these were due to combinations of disease pressure (from our wet June and July) and then the lack of rain in August. The fall color on these trees is limited as well.

Carotenoid pigments, responsible for the yellow and orange colors, are always present in leaves but are not visible for most of the year because there are larger amounts of green chlorophyll. As chlorophyll degrades, the yellowish colors become apparent and give leaves part of their autumn splendor as seen in Norway maple, Ohio buckeye, yellow poplar, sycamore, birch, hickory, ash and many other trees.

Tannins cause the brown hues in leaves of some oaks and other trees. The golden yellow produced in some leaves such as those of beech, result from the presence of tannins along with the yellow carotenoid pigments.

Anthocyanin pigments are responsible for the pink, red, and purple leaves of sugar and red maple, sassafras, sumac, white and scarlet oak, winged euonymus, and many other woody plants. Anthocyanins are usually not present in leaves until they are produced during autumn coloration. A few trees, however, such as “Crimson King” Norway maple and purple European beech have reddish leaves throughout the growing season due to anthocyanins. The production of anthocyanins is favored by warm, bright, sunny days, followed by cool nights with temperatures below 45 degress in fall, but not freezing.

So far, we’ve had some great sunny days with cool nights. These are the perfect conditions for a grand show this fall.

To follow the colors and plan your country drive on the peak day, go to: http://fallcolor.ohiodnr.gov.