Fall Foliage Explained!

by Thayer Nursery

We all know that New England has great autumn color, but did you know that we have the most spectacular display in the world? It’s because of the wide variety of deciduous trees and the climate here, with each autumn bringing bright, sunny days and cool nights. To understand why leaves change color this time of year, we have to start at the beginning…

Through a process called photosynthesis, plants absorb energy from light to convert water and carbon dioxide into glucose and oxygen. It’s a green molecule, chlorophyll, which enables this reaction and gives leaves their summer color. Autumn’s shorter days trigger a layer of cells at the base of each leaf to swell and separate it from the tree. Without a steady flow of water from the tree to replenish it, the chlorophyll disappears, revealing xanthophyll (yellow) and carotene (orange) pigments that have been there all along!

You may be thinking “yellow and orange, sure, but what about red?” Well, red is a different story. In some trees, like a variety of maples, glucose is trapped in the leaves when the separation layer swells. This trapped glucose is then used to produce anthocyanin, a red pigment. Scientists believe that anthocyanin helps trees retain their leaves longer by acting like antifreeze and lowering their freezing point!

It’s the combination of all these biological processes and different pigments that produce our enviable autumn color display!

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