Colors usually peak around the third weekend of October, but Mother Nature is a woman of mystery. “It’s always questionable until the last minute what will happen,” said University of Missouri Extension horticulturist David Trinklein. “Fall color is like Christmas morning. You don’t know if you are going to get an orange or a lump of coal in your stocking.”
Some years are better than others, and about once a decade colors really pop, Trinklein said.
Missouri’s size and diverse landscape make it possible to follow the color from one part of the state to the other. Leaves, shrubs and vines turn colors at different times. Color changes begin in northern Missouri and move south.
Different tree species have starring roles in different parts of the state. Sugar maples are the heavy hitters of fall foliage color. They burst with yellows, golds and reds along limestone bluffs bordering the Missouri River. Other species such as hickories, yellow poplar and persimmon light up the landscape with their lush yellows and golds. Not to be left out of the show, oaks add rustic reddish-browns for contrast.
There is a science to the changing of leaves, Trinklein said. Leaf shedding is part of a dormancy process the trees need to survive the winter.
During the spring and summer, leaves make food for the trees. Chlorophyll, a green pigment in the cells of the leaves, absorbs sunlight to transform carbon dioxide and water into carbohydrates such as sugars and starches through photosynthesis.
The shorter days of late summer trigger dormancy. A layer of cells known as an “abscission layer” forms where the leaf stem, or petiole, attaches to a branch or twig. This blocks metabolites from entering or leaving the leaf.
Two things that greatly influence leaf color happen as a result. Sugars, still manufactured by the leaf but blocked from leaving, turn into colorful pigments, usually red or purple. Additionally, chlorophyll starts to break down. That is when yellow and gold pigments get to shine. These pigments are present throughout the growing season but are masked by chlorophyll’s dark green color.
Leaf color intensity depends upon temperature, light and water supplies throughout the year. Color-watchers favor a steady supply of mild, sunny days and cool but not freezing nights for the best chances for fall brilliance. Leaves also need some moisture for colors to intensify.
Contrary to popular belief, frost is not necessary for trees to begin their color show, Trinklein said. Early frosts may even tarnish leaf color.
The mystery this year is about to unfold as Mother Nature dances across Missouri with her paintbrush. “Whatever the outcome, fall leaf colors are a treat we are privileged to witness only once each year,” Trinklein said. “Therefore, take time to enjoy them.”
For more information, including tips for leaf-watching in Missouri, see the MU Extension guide “Autumn Colors” (G5010), available for free download at http://extension.missouri.edu/p/G5010.
For the Missouri Department of Conservation’s latest report on fall colors, go to http://on.mo.gov/2dhooc2.