The Science Behind Fall Color

The brilliant colors of deciduous trees and shrubs display in fall are actually the grande finale of the compliceted process of photosynthesis. That's how plants produce food. It takes place in the leaf cells that contain chlorophyll, the pigment that makes leaves green. Leaves make chlorophyll all through the growing season. But as temperatures get cooler and the days get shorter, chlorophyll production slows down and eventually stops. As the chlorophyll declines, the green starts to fade away, revealing pigments that had been hidden by green. This is when the show begins.

Carotenoids are yellow pigments that turn aspens and ginkgos stunning shades of yellow and gold. Tannins are responsible for the dull browns of some oaks. And since all leaves contain at least some tannin, that's why most of them eventually turn to brown, especially after they fall to the ground.

Anthocyanin turns maples red and dogwoods purple. It's a bit more temperamental than the other two pigments, and needs lots of sunlight to reach its colorful peak. If the leaf doesn't get enough sun, the color stops at yellow, orange or even brown.

Of course temperatures come into play as well. Early freezes reduce colorful foilage because the leaves are killed before they can go through this elaborate process. Long, warm fall days and bright sun will create the most colorful fall show.

Yellow Foliage

Aspens