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The Homeowners Column
Colorful Autumn Leaves - Predicting and Planning
State Master Gardener Coordinator
Passionate gardeners possess a perpetual bend at the waist. We look, we weed, we plant. We don't stand erect until autumn. The trees we barely noticed all summer grab us by the nose in fall and say "hey look at me!" As winter approaches the green chlorophyll in leaves steps aside to let the yellows and reds take center stage. Unlike the vivid colors of flowers that attract pollinators, changes in leaf color appear to have no biological importance. It's just a happy by-product of seasonal shift. I think it's a consolation prize for us plant geeks who are reluctant to say goodbye to another growing season.
People, also known as "leaf peepers," plan vacations around the best fall color. Luckily we don't have to travel far for a good show. Fall color does vary depending on plant genetics, health of the tree during the growing season, weather, and changes in daylight. The sun and the earth have taken care of the daylight length issue. Each year after June 22 the length of daylight grows progressively shorter. Plants respond to certain daylight lengths, but not all species and not even all individuals in the same species respond exactly the same.
A plant's genetics trumps all the other factors for predictable fall color. Ginkgos, larch, tulip poplars, hickory, and birch are always some shade of yellow. Their yellow colors don't vary much from year to year but the hot dry summer pushes leaves to be more of a sickly yellow/brown. The yellow, orange, and brown colors of the carotenoid pigments are already present in the leaves, but go unnoticed until the green chlorophyll is no longer produced.
Red colors tend to be less predictable than yellows. Sunny days and cool nights intensify red colors. Bright sunlight is crucial for production of red pigments. Often this creates a magnificent halo of red where the outer or upper leaves are red and lower, less exposed leaves are yellow.
Our hot dry summer turned many leaves a crispy brown so bright colors may be ringed in brown. The worst condition for good fall color is a severe cold snap before leaves have a chance to turn colors.
If you want a plant with good fall color, purchase the plant in the fall when the plants are showing off. Great variability exists in many plants traditionally known for fall color. For instance red and sugar maples may be a brilliant clear yellow or multi-shades of red and yellow. Burning bush may be pink or red. Or select named cultivars. Look for names such as 'Autumn Blaze', or 'Red Sunset' red maples.
Our native white oak is a gem with its maroon color of fine aged wine. Ginkgo leaves turn a clear yellow then hold hands and dive off the tree all at once. Blackgum is one of the best and most reliable fall performers with its leaves of yellow, orange, scarlet, and purple in a tangled collage of color.
For red/purple/orange fall color - White Ash (some cultivars); Sugar Maple (variable); Black, Red, White, and Scarlet Oaks; Dogwoods; Hawthorns; Sassafras (variable); Serviceberry; and Sweetgum.
For yellow fall color – Beech; Birch; Magnolia; Norway Maple; Red Maple (variable); Sugar Maple(variable); Silver Maple; Buckeyes; Catalpa; Hackberry; Persimmon; Kentucky Coffeetree; Willow; Linden; Elms; Honeylocust; Tuliptree; Bur Oak; Sassafras (variable). Perennial flowers of willow leaf amsonia and balloon flower.
If a pile of colorful leaves produces only visions of work for you, than you need to take a walk. Join me along with Bill VanderWeit and John Karduck, the previous and present city arborists with the city of Champaign, on Saturday October 20, 2012 from 9 am-noon for the University Avenue Tree Walk in Champaign. Meet on the corner of University Avenue and Victor, just one block east of Mattis Avenue.