Help your trees look spectacular in autumn
The time when trees change color and then drop their leaves is a signpost of the year, a mark of the familiar cycle of the seasons.
Early to mid-October is typically the height of the color in northern Illinois, according to EdHedborn, manager of plant records at TheMorton Arboretum in Lisle. But many factors — especially theweather— affect the timing and whether this year’s range of color will be spectacular or so-so.
Trees change color as they prepare to become dormant. When they sense days growing shorter toward the end of summer, they start to temporarily shut down many of their functions to protect themselves fromthe perils of winter and conserve resources until spring. Plants throughout theworld use dormancy to get through bad times. For example, in equatorial jungles, plants often go dormant during the dry season.
“Whenever trees are under stress, they may cope by going dormant,” Hedborn said. That’s why theweather all through the year can affect the fall color season.
This year, for example, a wet springwas followed by a hot and dry July and August. Some trees reacted to the stress of heat and drought by starting dormancy early, dropping their leaves over the summer. Those treeswon’t be part of the fall color chorus.
It’s not justweather that determines howcolorful fall trees can be. The types of trees in an area make a big difference.
“Each species of tree or shrub is genetically programmed to turn a particular color or range of
colors,” Hedborn said, from the yellowof buckeyes to the orange of serviceberries to the bright red of sumac and the deep burgundy of some kinds of oaks.
In Colorado’s Rocky Mountains, most deciduous trees are aspens, which can only turn a clear yellow. In the Midwest and NewEngland, sugar maples, which can also turn red, mix that color with yellowto produce all the colors of the sunset. At the Arboretum, where trees fromall over the world are planted together, there’s potential for an even wider variety of colors— if theweather cooperates.
In general, the tree color showis most grand when late September and early October bring adequate rain, sunny days and cool nights, Hedborn said. A hot or dry September can make the fall tree color early or muted. A big fall storm can blowmost leaves down and end the showearly.
Why do trees change color at all? It’s basically a byproduct of entering dormancy. As they prepare to shed their leaves, trees stop producing chlorophyll, the chemical that powers photosynthesis and also makes leaves green. As the green chlorophyll drains away fromeach leaf, its underlying color can be seen. In most leaves, those underlying colors are yellowor brown.
The red pigment that