Summer’s extreme heat, drought could diminish fall colors

Joliet — Summer may be in its final days, but the season’s extreme, erratic weather may still have an impact on Illinois’ fall colors.

Spencer Campbell, the plant clinic manager at Morton Arboretum in Lisle, noted 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.

“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.”

While the full spectrum of the summer’s impact has yet to be seen, some, like Autumn Blaze maples, have already been affected and have begun their autumn transformation early at both the Morton Arboretum and in Joliet.

“I saw some of the maples starting to change earlier this week, and it’s because they’re stressed,” said Joliet city arborist Jim Teiber. “When they get too dry from drought conditions, the photosynthesis process slows down and colors come earlier.”

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.

“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.”

—  Christopher Evans, forestry and research specialist with University of Illinois Extension

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 while 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.”

Keeping trees healthy

While fall colors might come early and move fast this year as a result of the hot, dry conditions, Evans said the stress is not something to worry about for most older, well-established trees.

“Trees are more flexible than a lot of other plants because they have bigger, more extensive root systems. Droughts impact them, but not as dramatically, unless you have prolonged stress for more than a year or two,” he said.

The same does not necessarily apply to young trees, or trees that have recently been transplanted, which he notes are more susceptible to stress damage and need more attention and care in drought conditions.

Those conditions often apply to parkway trees, which are smaller and are often planted in dryer soil and harsher conditions. Teiber said that during drought periods it is a good idea to water small trees in yards and parkways to ensure they stay healthy.

“If the trees dry out and drop all their leaves too early, they might not be able to store up enough energy to fully leaf out again in spring, and it can eventually catch up to them and kill them,” Teiber said, while noting that even trees that lose their leaves early can still recover if the tips of the branches retain their greenery into fall.

“We ask residents to water their trees during droughts and heatwaves to prevent that. You don’t need to worry about your lawn because it will bounce back, but you should really let the trees soak,” he said.

While watering during the hot summer months is ideal, Teiber said that even as the trees begin to change colors in September and October, it can still help them to provide extra water.

While the schedule of the fall colors may be different this year, Campbell still suggests visiting neighborhood parks, trails and arboretums throughout the season to make the most of the color we do get.

“Fall leaf season is already underway at the arboretum and really every week is a different color display, from the maples now to the oaks in late October,” he said.

While some trees may already have gone through their metamorphosis, Campbell said that late September and early October around Columbus Day should still be great times to get out and appreciate the colors.

He recommends checking the fall color tracker on the Morton Arboretum website to see which trees and other plants may be changing and worth looking for week to week in northern Illinois.