Don Kinzler, Published October 04 2013
Mother Nature's Masterpiece: Cool nights. sunny days help bring intense colors to autumn foliage
Understanding the cause of fall color adds to the appreciation of the season as trees and shrubs enjoy one last colorful fling before winter. And it makes for good trivia talk. Now you’ll know the answer to the childhood question of “Why do trees change color?”
Fall color and its intensity is based on three factors: day length, leaf pigments contained in different plants and weather. During the growing season, leaves are factories where food necessary for tree growth is manufactured. This food-making is carried out by small cells containing chlorophyll that give leaves their green color.
As autumn approaches, shorter day length signals to plants that winter is coming. The machinery of the leaf factory is dismantled and green chlorophyll breaks down. As green pigments fade, others are uncovered.
Nearly all leaves contain yellow pigments called carotenoids. Trees and shrubs displaying yellow fall color have simply had the pre-existing yellow pigment unmasked by the breakdown of the green chlorophyll. Because these pigments are always present in the leaves, yellow and gold fall colors remain fairly consistent each year because they are triggered by the calendar’s short days.
Some trees and shrubs turn red, orange or scarlet, as determined by the plant type and weather. When night temperatures begin consistently dropping below 45 degrees, the flow of sugar within the plant begins to stop. Sugars are trapped within the leaves. Chemical reactions convert sugars into red and purple pigment called anthocyanin. This process does not occur in all plant types, which explains why sumac turns red but birches turn yellow.
The most spectacular color displays are produced following a succession of warm, sunny days and cool, crisp, non-freezing nights. Lots of sugars are trapped in the leaves, leading to a major conversion to red pigments. Orange and copper tones are created by a blending of the red anthocyanin that has been produced with the yellow carotenoid pigment that is ever-present.
When it comes to autumn’s colorful display, Jack Frost actually does more harm than good. As woody plants are preparing themselves for winter, a layer of cells begins to form at the point where leaf stems (called petioles) are attached to the twigs. This layer allows leaves to fall from the plant before winter.
Think of the mess if all the dead brown leaves clung to the trees all winter. Frost hastens the leaf-drop process. Just when we’re in the middle of a really good autumn color show, too many freezing nights cause leaves to detach from twigs and begin falling.
Landscaping for fall color
To create a picture-postcard scene of autumn, combine yellow, red, gold, and orange highlighted against evergreens. Local nurseries offer a plentiful selection of hardy plant material from which to choose. The following are some of the best hardy trees and shrubs for fall color landscapes.
Fallgold ash (golden yellow), prairie spire ash (yellow), prairie dome ash (yellow), northern treasure ash (yellow), Dakota pinnacle birch (yellow), prairie dawn birch (yellow), northern tribute river birch (yellow), northern acclaim honeylocust (yellow), prairie torch buckeye (orange-red), prairie stature oak (red), prairie expedition elm (yellow), northern flare sugar maple (orange red), autumn blaze maple (red), firefall maple (scarlet), northern red oak (red), prairie sky poplar (yellow), hackberry (light yellow) and larch (yellow).
Flame amur maple (red), prairie horizon alder (yellow), prairie radiance euonymus (red), quaking aspen (yellow), prairie gold aspen (golden yellow), Canada red cherry (purple in summer, red mix in fall), juneberry (gold and scarlet).
Fireworks amur maple (scarlet red), carousel barberry (red), rosy glow barberry (purple in summer, red mix in fall), winged euonymus burning bush (bright scarlet), cotoneaster (orange red), Alaska viburnum (red), gary viburnum (red), sumac (scarlet), gooseberry (copper orange), Siberian pearls dogwood (purple red), summer wine ninebark (purple in summer, red mix in fall), cotton candy smokebush (scarlet).
Isn’t Mother Nature awesome? And nowhere is her hard work more evident than in a brilliant display of autumn color. To avoid hurting Jack Frost’s feelings, I must say I enjoy the swirly ice patterns he sometimes creates on winter windows, but I wish he would leave Mother Nature’s autumn marvel well enough alone.
Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler’s Greenhouse in Fargo. Readers can reach him at email@example.com