LISLE, Ill. (March 14, 2024)— February’s record high temperatures and the overall warm winter spurred unseasonably early spring blooms in the Chicago region, with some trees and plants flowering more than a month ahead of schedule, according to scientists at The Morton Arboretum.

“If a late freeze hits, trees and plants that flowered too early have a higher risk of damage,” said Christy Rollinson, Ph.D., forest ecologist at the Arboretum. “Some elm and maple trees flowered in late February. These trees typically bloom in April across the Chicago area, so this is very early.”

The timing of blooms and leaf out is one of the most consistent indicators of climate change locally and globally, Rollinson said. While El Niño helped accelerate the arrival of this year’s spring blooms, she credits climate change with generally causing progressively earlier spring blooms and leaf out.

“This variability among species—both plant and animal—is one of our greatest concerns about climate change impacts on ecosystems,” Rollinson said. “Because species may have different sensitivities to temperature, there’s the potential for climate change to shift bloom time disproportionately with pollinator or bird migration timing, among other concerns.”

If trees, shrubs or perennials that bloomed early experience winter injury or frost damage, they are unlikely to die completely and will come back from the roots, said Spencer Campbell, the Arboretum’s Plant Clinic manager. Trees and shrubs are likely to lose some flowers, but leaves should emerge without an issue, he said.

“If leaves become damaged by frost, they will try to refoliate,” Campbell said. “They will need plenty of water to do that. By the end of the season, if there are enough water resources, you should not be able to notice any difference.”

To help protect small plants from frost damage when below average temperatures are predicted, consider covering them with a tarp or sheet that touches the ground in order to trap the heat, he said. Remove the tarp or sheet the next day once temperatures rise. Those with questions or concerns about freeze damage and how to care for trees and plants can contact the Arboretum’s free Plant Clinic for advice by phone or email.

Spring showstoppers

Timing of spring blooms is largely controlled by temperature, meaning the weather over the coming weeks will more clearly show exactly how early the region’s blooms are, Rollinson said. In April to mid-May, woodland wildflowers and the majority of flowering shrubs, as well as crabapple, cherry, magnolia and serviceberry trees, are expected to be blooming throughout the area. The Arboretum offers a weekly Spring Bloom Report with information about the spring flowering already underway.

Cicadas

The warmer temperatures may also impact when the 17-year periodical cicadas emerge, according to Stephanie Adams, the Arboretum’s plant health care leader. Cicadas emerge when the temperature at 8 inches below the soil line is above 64 degrees Fahrenheit. In the Chicago area, 17-year cicadas typically surface in May, but with warmer temperatures, they could emerge sooner.

Cicadas are not a threat to people, animals or healthy mature trees and shrubs. However, they can harm young and other vulnerable trees and shrubs when female cicadas cut slits into twigs to lay their eggs.

“We recommend homeowners plan ahead for the cicadas by identifying preferred host plants and making a protection plan for susceptible trees and shrubs,” Adams said. Protection measures include ensuring that vulnerable trees and shrubs are healthy in the spring and covering small trees and shrubs, including those with few developed branches, with a fine protective netting, such as tulle fabric. According to the Arboretum, it’s best to apply the netting after leaves emerge, when they are fully expanded and hardened off, and before the cicadas emerge.

For more expert tips about trees and cicadas, visit mortonarb.org/cicadas.