Why Leaves Turn Colors
Vermont is famous for it's spectacular autumn foliage. Visitors (aka leaf peepers) to this tiny rural state in the northeastern United States sometimes book a year in advance for the pleasure of viewing this once a year colorful display. Sometimes however, the leaves aren't so spectacular and simply turn brown and fall off the trees.
Unusual? Perhaps, but certainly not unheard of. Leaves contain two different color pigments, green and yellow-orange. Green is caused by the presence of chlorophyll and yellow-orange by the presence of carotenoids (the same pigments that make carrots and pumpkins orange).
During the summer when plants are actively growing, leaves produce chlorophyll (which is needed for plants to make food) and the leaves appear green. Chlorophyll masks the presence of the carotenoid pigments. At the end of the growing season, chlorophyll production slows down and there are fewer chlorophyll pigments. As a result, the carotenoid or yellow-orange pigments in the leaves are revealed.
A third pigment called anthocyanin is responsible for the red color that shows up in autumn leaves. This red pigment may be present naturally or produced when excess sugars (food) remain stored in the leaves.
Shorter days that are warm and sunny combined with longer nights that are cool but not frosty are the ideal conditions for producing a colorful autumn display. So when it rains and is cloudy and gray for days on end, it definitely affects the leaves changing color. Bad news for leef peepers.
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