Fall colors in Chicago area expected to peak in mid-October, experts say

After a summer of basking in the sun, Illinois’ foliage is expected to begin swapping its green hues for warmer tones of yellow, red and brown as early as late September. The flamboyant display is expected to reach its peak in mid-October.

With sunlight thinning in the Northern Hemisphere, trees produce less sugar, which causes their leaves to change to their traditional autumn shades before falling to the ground.

Nick Kuhn of Cook County’s Forest Preserve said tree leaves actually bear those colors year-round, but their tones are masked by the green pigment of chlorophyll, a chemical by which the trees convert sunlight into food and energy.

In a way, Kuhn said, the color change is how leaves say, “We’ve had enough, here’s who we really are.”

Sunny days, crisp evenings and a generous amount of rainfall help create lavish displays of fall color, Kuhn said. Luckily, one of the driest Illinois Aprils on record in more than three decades was followed by sustained rainfall throughout the tail end of summer, he said. But that early dry spell still elevated the stress levels of some trees — putting them at greater risk of early leaf-shedding.

Chicago Botanic Garden plant curator Jessica Goehler has been watching some leaves of the maples and honeylocusts on their grounds change colors. She noted some trees in the garden are showing signs of residual stress from dry spells over the last several years, which can potentially contribute to premature leaf-dropping in the future.

But since trees store nutrients and reserves of water, Goehler said the effects of this year’s extreme weather won’t be visible until a couple of years from now.

Tree experts concur that this year’s fall holds promise, so long as parts of Chicago don’t freeze prematurely.

Goehler recommends looking out for different maple trees throughout the city and suburban Chicago “which pull off that bright red foliage.” Maggie Daley Park is an urban observation staple, she said.

Red and black oaks are another classic, which can be found throughout Cook County’s Forest Preserves, Kuhn said.

Some recommended fall color observation spots:

• The River Trail Nature Center near Des Plaines
• Deer Grove Forest Preserve near Palatine
• The Morton Arboretum in Lisle
• The Swallow Cliff Stairs near Palos Heights

Kuhn also recommends looking out for katsura trees. Originally from Japan and China, these trees can be found in the Chicago Botanic Garden. The katsura’s heart-shaped leaves take on an apricot-yellow shade this time of year and produce a scent reminiscent of cotton candy or caramelized sugar.

Goehler calls hickory and walnut trees the season showstoppers, which are expected to blaze golden toward the tail end of the fall color season.

Anna Savchenko is a reporter for WBEZ.