Fall Colors

While researching our trip to Boston, Massachusetts and Vermont last year, I came upon a clear and concise description of how leaves turn colors in the fall, posted on the Stowe Fall Foliage web site. It is simplified, without bringing in the intricate interplay of plant hormones and environmental conditions that you might read about in a botany book. Here is the simplified version, with full credit going to the Stowe Fall Foliage site.

Yellow, orange, and red leaves in mid-Vermont

On the longest day of the year, June 21, chemical changes begin in the tree that later produces the fall foliage colors. As the days grow shorter and temperatures drop, green chlorophyll moves from the leaf to the branch, revealing the yellow and orange pigment that was always in the leaf. Warm fall days produce sugar, which is trapped in the leaf when the temperature drops at night. The leaves turn hues of red as the sugar accumulates. The article then describes the colors you can expect to be produced by leaf type in Vermont:

• Red (and some yellow) – sugar maple, red maple, red oak, sweet gum, black gum and sourwood
• Gold and yellow – birch, elm, poplar, redbud and hickory
• Maroon – sumac

Gold and yellow leaves near Hildene House in southern Vermont

If you want a little more information about the interplay between plant hormones and environmental conditions needed to produce fall colors, I recommend Botany for Gardeners by Brian Capon. He describes the processes and conditions at work to produce fall leaf colors, prepare for leaf drop, drop the leaves (the leaf scar prevents sap from bleeding out), and go dormant.