Fall forecast: Will it be a bright year or are trees in KC area destined to be blah?
As cool temperatures make an appearance in the Kansas City area, the leaves also begin to show signs of changing. Will this season be filled with color? The wide swing in weather patterns makes it difficult to predict the intensity of fall color in the metro.
Steady rainfall occurred throughout the summer months, nourishing the trees and shrubs. However, the warm and dry September and early October are not favorable conditions for a brilliant fall season. Why some leaves become brilliant with fall color is determined by science and the environment.
The presence of chlorophyll in the leaves produces natural sugars required for plant growth and gives leaves their green appearance. Other pigments contained in the foliage include carotenoids and anthocyanins. All trees contain chlorophyll, but whether a tree possesses carotenoids or anthocyanins depends on plant genetics.
Carotenoids are responsible for yellow and orange pigments in the changing leaves. These colors reveal themselves when chlorophyll production stops in the fall. Anthocyanin pigments result in the development of purple and red fall colors. These pigments form when sugars become trapped in the leaf.
Long nights and cooler temperatures result in two changes in the leaf; chlorophyll production stops and an abscission layer develops. This layer seals off the nutrient flow from the leaf to the branch, trapping sugars and causing the leaf to drop.
This natural process is impaired by cloudy, rainy days and rapid temperature changes. Freezing conditions halt the process, resulting in a lack of pigment development and an improper abscission layer. If this layer does not form, the leaves wither without falling and hang on the trees long into winter with a dull, brown color. This phenomenon is referred to as a marcescent autumn.
Fall color is determined by environmental conditions not only in fall but all summer long. The best fall color begins during the summer months with ample rainfall. Late summer and fall rain are accompanied by cloudy weather, reducing pigment development. Cool temperatures and bright sunny days in September and October are the ideal combinations for stunning fall color.
Environmental conditions are one part of the equation. Genetics or tree species is the other factor. The Kansas City area is not known for native species that develop anthocyanins. Native species like elm, oak, hickory, hackberry, redbud and sycamore found in our woodlands genetically produce more carotenoids. This results in shades of yellow. A few native species like sumac, vining Virginia creeper and poison ivy tend to develop shades of purple and red.
Introduced non-native species are striking in the landscape as they produce more anthocyanins resulting in the desired purples and reds. These species include red maple, sugar maples, sweetgum and black gum. Many shrubs like burning bush, viburnums, spirea and fothergilla are planted for fall color.
It is challenging to predict peak fall color in Kansas City as weather patterns play a large role. Typically, color develops in the third or fourth week of October and continues into early November. Time will tell if the trees will be an impressive show or a bust.
Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Have a question for him or other university extension experts? Email them to garden.help@jocogov.org.
