Fall leaves’ colors depend on weather, experts say

Conditions over the summer, and fall rain and temps, will factor into how vibrant the tree canopy gets in the next few weeks

A few leaves on a Maple tree near Harvard start turn yellow on Thursday, Sept. 7, 2023. Fall colors are just starting to show up in McHenry County.

Arborists said this year’s unpredictable weather patterns in Illinois are having an effect on leaves’ colors this fall, causing earlier changes that may not be as vibrant.

Spencer Campbell, the plant clinic manager at Morton Arboretum in Lisle, noted that this summer had a lot of extreme weather, swinging between drought conditions early and then heavy rains.

April, May and June reportedly only saw half of their usual annual rainfall, while July received twice its annual average and August came in below average while accompanied by extreme heat, Campbell said.

“These sorts of stress events can definitely impact fall color,” said Campbell, “though it remains to be seen how the 2023 drought will impact the fall colors. Last year we had beautiful color at the arboretum because there was a lot of predictable, typical weather. This year was much less predictable. The next few weeks will be important. If we get mild weather, it should give us some good fall color.”

The next few weeks will be important.”

—  Spencer Campbell, plant clinic manager at Morton Arboretum in Lisle

In McHenry County, Wendy Kummerer, director of marketing and education with the McHenry County Conservation District, said week-by-week color changes will depend on evening low temperatures and the amount of precipitation.

Less rain typically means “brown and down,” she said.

Usually, full color in McHenry County arrives during the second to third week in October.

“Peak leaf color depends upon many factors, and some years color is less brilliant and for a shorter period of time than in previous years,” Kim Compton, education and visitor services coordinator at the district, said in an article found at Landscapes, an online and hard copy magazine produced by the district. ”Drought, flooding, hot temperatures and cold can all affect the intensity of the colors. Usually in McHenry County we begin to see the reds in September, the orange and some of the yellow in October, and then the peak of the oaks happens in mid- to late October. You are likely to see beautiful color throughout the fall.”

Compton recommends that people make trips out to local wooded areas often during this season.

As trees reduce their photosynthesis for the season, the amount of green chlorophyll in the leaves is reduced, revealing the dramatic array of reds, yellows, oranges and browns seen in fall leaves, a sign that the tree is going dormant for the season.

University of Illinois Extension forestry and research specialist Christopher Evans said this effect is “basically the trees just giving up for the year,” and noted that although some will begin to show their color early after a stressful summer, it also means that the overall fall color season could be shorter and less vibrant.

“Early color won’t be fantastic color,” Evans said. “The stress will sometimes just make them brown faster and then drop their leaves. A little drought stress through a season can lead to really nice color, but I think there was so much stress this year that I’m not expecting the best season.”

The conservation district compiled a list of areas to visit this fall to enjoy the colors of fall at MCCD.me/FallFrolics.

A national fall foliage map is located at smokeymountains.com/fall-foliage-map.