Why Fall Colors?

Nature

Leaves change from green to spectacular yellows, oranges and reds because of a chemical process that takes place in the tree as the seasons change from summer to winter.

In spring and summer, the leaves serve as factories that manufacture most of the foods necessary for the tree’s growth.

Numerous cells in each leaf contain the pigment chlorophyll, which gives the leaf its green color. Along with the green pigment, leaves also contain yellow or orange carotenoids, the same chemical that gives the carrot its orange color.

Most of the year, these yellowish colors are masked by the greater amount of green coloring.

But in the fall, partly because of changes in the period of daylight and changes in temperature, the leaves stop their food-making. The chlorophyll breaks down, the green color disappears and the yellowish colors become visible.

Chemical changes form additional pigments to create the reddish and purplish fall colors of dogwoods, vine maples and sumacs and the orange and fiery red of sugar maples.

Warm sunny days followed by cool nights with temperatures below 45 degrees are perfect conditions to produce red fall displays.

Sugar is made in the leaves during daytime, but cool nights prevent movement of sugar from the leaves. Sugars trapped in the leaves form the red pigment called anthocyanin.

The degree of color may vary from tree to tree. For example, leaves directly exposed to the sun may turn red, while those on the shady side of the same tree or on other trees in the shade may be yellow.

Also, the colors on the same tree may vary from year to year, depending on the combination of weather conditions. Less red coloration occurs in periods of warm, cloudy or rainy fall weather.