Plant Exchange Blog

Transitions can be a challenge when we adjust our clocks in fall. Deciduous trees have fall adjustments too, and the fall color that we enjoy, is one of them.

Trees and shrubs that die back in fall usually have green leaves into Fall. Then, while days are warm, the evenings become cool, sometimes with light frosts. Foliage can’t take a heavy frost, so the plants cut their losses, by dropping leaves.  Before they do, we notice leaves change color. This cottonwood tree by the Missouri River in Lewis & Clark Recreation Area is just beginning to change to its golden yellow.

What is happening? Plants need to carry on photosynthesis that uses green chlorophyl as long as possible. Plants also need to shuttle nutrients such as sugar from the leaves to winter storage in woody branches and roots before a killing frost kills the leaves. Red-orange-yellow anthocyanins and carotenoids help move the sugar, help leaves hold on to water in this fragile time, and protect leaves in early frost. 

This native gray twig dogwood has produced white berries for wildlife to help plant seeds and the leaves are changing color day by day as the energy is being transported for storage until next year. It’s happening now with deciduous trees and shrubs outdoors.

Once transport of nutrients out of the leaf is done, a layer of cells between the leaf and the stem is sealed off, and the leaf dies and falls to the ground.

Some years the colors of fall are more or less bright. Dr. John Ball, tree specialist and professor at South Dakota State University, said that it takes a healthy maple to turn from green to red in fall. The drought in our region is stressing trees and may impact leaf colors this fall. Watering all trees and shrubs before winter may help plants under the stress of the exceptional drought we experience this season.

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