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AUBURN UNIVERSITY, Ala.—Now that fall has arrived in Alabama, temperatures are dropping and leaves are changing colors. Vibrant red, sunny yellow and bright orange leaves are falling. The colors should peak in early or mid-November, depending on the amount of cool weather between now and then.

Why does leaf color change in the fall?

Green and Yellow Leaves

“The green color of leaves is caused by a pigment called chlorophyll, which helps trees make food,” said Mallory Kelley, a regional horticulture agent with the Alabama Cooperative Extension System.

During the fall, the leaf will begin to separate from the branch. This happens as less sunlight and cooler temperatures gradually cut off water and nutrients. At this point, leaves stop manufacturing chlorophyll and the leaf begins to break down. This process begins the color changes. 

Some trees like hickories and ginkgo trees will only make yellow foliage and don’t have the ability to produce reds and oranges.

“Fall colors are always present in leaves but the green of the chlorophyll covers them,” Kelley said.

Red Leaves

The pigment carotin causes the yellow-orange color and exanthophyll causes the golden yellow. The pigment anthocyanin produces the red in leaves. It results from the accumulation of sugars and tannins in the leaf.  Red leaves are visible on the sunny side of the tree and yellow leaves appear on the shady side.

Reds and oranges will only appear when there are cool nights in conjunction with warm sunny days; otherwise, all of the foliage will be yellow and brown.

Color is a byproduct of chemicals produced by sugar formation in the leaf. Temperature and the amount of sunshine the plant gets are also important factors. Good growing conditions help produce more sugars, which results in richer leaf colors.

More Information

Find more information by visiting www.aces.edu.

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