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The Homeowners Column
Predicting Fall Color Is No Easy Task
Extension Educator, Horticulture
Once a year the trees demand our attention. The trees we barely noticed all summer grab us by the nose in autumn and say "hey look at me!" In the fall the green chlorophyll in the leaves steps aside to let the yellows and reds take center stage. Interestingly unlike the vivid colors of flowers which are necessary to attract pollinators, there seems to be no biological importance to color change. It's just a by-product of a seasonal change from growing season to dormancy. A splash of fall color—what a great way to say goodbye to another growing season.
Each year all kinds of people make predictions as to how good the fall color will be and when the fall color will appear. Predictions are tricky. Good fall color depends on adequate rainfall through the season, a good growing season, fall weather, plant genetics, and changes in day length. The sun and the earth have taken care of the day length issue. Each year after June 22 the length of daylight grows progressively shorter. Plants respond to certain day lengths, but not all species and not even all individuals in the same species will respond the same to day length. There isn't an alarm that goes off in each maple as soon as the day length reaches 12 hours. Plants react on a flexible nature time, not a digital watch human time.
With plant genetics in relation to fall color, some trees are predictable in their color. Ginkgos, redbud, larch, tulip poplars, hickory and birch are always some shade of yellow. Some plants are much less predictable. Maples, sassafras, sweetgums and ash can be yellow, red or combinations.
Fall color is also affected by the weather while the leaves are changing. If we get into a dry spell with hot winds, the leaves may just stay a sort of pale green and then fall off. If we get an early freeze, the leaves may just turn black and fall off.
Sunny days and cool nights intensify red colors. Actually bright sunlight is crucial to the production of red pigments in fall leaves. Sometimes we see this as a two-layer effect where the outer or upper leaves are red and lower, less exposed leaves are yellow.
If you have decided you want a plant with good fall color, it is best to purchase the plant in the fall. There is great variability even in plants such as burning bush. Or select named cultivars. For red fall colors in red maples look for 'Autumn Fantasy‚' 'Red Sunset' or 'October Glory' or with white ashes look for 'Autumn Applause' (maroon), 'Autumn Blaze' (purple), or 'Royal Purple.' Other plants with good fall color include: serviceberry, black gum, bald cypress, Kentucky coffeetree, pagoda dogwood, hackberry, honey locust, larch, or blackhaw viburnum.
One of my favorites is white oak. They aren't the hot sports car red of burning bushes, but a fine aged wine red. I love the clear yellow of a ginkgo whose leaves seem to hold hands and dive off the tree all at once. One of the best and most reliable fall performer is black gum also called sour gum. Its leaves show yellow, orange, scarlet and purple. There are some nice examples of black gums on the U of I campus on Green Street west of the Illini Union.
Stop by our office at 801 North Country Fair Drive in Champaign or the Urbana Public Works building at 706 South Glover in Urbana for the State Street Tree Trail Guide. Spend a pleasant fall day on a walking tour of the older part of Urbana to discover 20 different species of trees. See which ones have nice fall color.