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The chemistry behind fall color
The Coast Gardener Newspaper and Web Column - October 27, 2001

Every fall we hope for beautiful shades of oranges, yellows, reds and purples to send ripples of color through the landscape. Some years we have a great show of fall colors, but other years we do not. The intensity of fall color can vary quite a bit from year to year. We are the last folks to usually enjoy the fall colors. Our growing season is longer than most areas; therefore, we have to wait a bit longer for the colors to burst onto the scene.

Have you ever wondered exactly what happens to cause these beautiful colors? Chemical processes in trees that occur this time of the year cause the leaves to change color. Let's first take a look at what happens in the leaf structure during the spring and summer.

Leaves manufacture their own food by a process called photosynthesis. Leaves produce this food in cells that contain chlorophyll. Chlorophyll is the green pigment that masks other colors during the growing season. Chlorophyll is a remarkable chemical that absorbs energy from the sun and uses it to manufacture sugar from carbon dioxide and water. The oxygen that we breathe is a by-product of this food-making process.

Remember I mentioned that chlorophyll masks other pigments? Xanthophyll is a yellow pigment and carotene is an orange pigment. For example, squash have yellow xanthophyll pigments and carrots have orange carotene pigments. You don't see these colors during the spring and summer because chlorophyll hides them.

As the days get shorter and temperatures cool off, leaves stop making food. Since the chlorophyll is no longer needed, it breaks down leaving the other colors visible. The yellows and the oranges that you see were really present in the leaves all along. Other chemical changes occur and produce even more colors that are so vivid in the fall. Anthocyanin is another pigment that produces the reds and purples in dogwoods, sumac, black gums and Chinese tallow trees.

Several factors affect the intensity of fall color. Temperature, water, light and chlorophyll residue all determine just how bright and striking the colors will be. These factors also determine how long the color will hang around, too.

Low temperatures above freezing favor anthocyanin formation. If your maple turns bright red, it is

likely that temperatures have dipped into the thirties or lower forties for a few nights already. An early frost is not good, as the colors will be less intense and frost damage can cause leaf drop.

Sunny warm days, cool nights and occasional rains produce the best fall colors. Unfortunately, some areas are a little dry, and this may hamper some fall color development.

I suspect the peak of our fall color is one or two weeks away, depending on what the weather does. Fall is a truly beautiful time of the year. Please take a few moments to enjoy the spectacular shades of color that will set the landscape ablaze this year. After all, here along the Coast we are only briefly visited by falls' wondrous color&emdash;even on good years.

These archived gardening columns were written by Chance McDavid, former Harrison County Extension Agent.