LISLE, Ill. (March 11, 2025)—Despite the drought conditions in much of Illinois, including abnormally low winter snowfall in Chicago, scientists from The Morton Arboretum say that weather permitting, trees and plants in the Chicagoland region are generally still on track to experience peak spring blooms around a normal time this year of mid-April to May.

“The current dry conditions don’t necessarily spell doom for this year’s blooms,” said Arboretum Forest Ecology Research Scientist Christy Rollinson, Ph.D. “Because plants are dormant and aren’t expected to emerge en masse for several more weeks, any rain or snow we do get in the coming weeks will have a big impact on water in the soil available to plants. Because plants aren’t active yet, steady rains on thawed soil will soak in and recharge soil moisture quickly. If that happens, trees and plants will have ample water available for when they start actively growing.”

Overall, Chicagoland has had fewer warm spells this winter compared to last year, when spring blooms and leaf out occurred unseasonably early for some trees and plants.

“Last year, we had a very warm winter that caused some plants like many maple trees to bloom and leaf out early, but we then had a cool early spring, causing other species like many of our oak trees to be normal,” she said. “Because we didn’t have many extreme warm spells this winter, we aren’t currently expecting a wave of very early leaf out, but it’s too early to tell what will happen for plants that typically emerge in late April through May.”

Spring bloom timing is mainly influenced by temperature. However, some early-blooming and hardier plants that can withstand a higher risk of being exposed to a deep freeze, such as common witch-hazel shrubs and the skunk cabbage plant, rely on their internal clocks instead and have consistent blooming times each year. Generally, plants that bloom later in spring, like magnolias and Japanese cherry trees, are more affected by temperature fluctuations.

Although almost all modeling and predictions of spring bloom timing tend to be based on air temperature, scientists at the Arboretum and elsewhere are increasingly looking into the role of soil temperature and moisture on leaf out, Rollinson said. Water is needed to allow the cells in flowers and leaves to expand and soil temperatures are important for the timing of spring understory plant emergence, she said.

“Soil-related datasets are much harder to find,” Rollinson said. “However, drought-focused research at the Arboretum has shown that in 2023, which had a very dry spring, plants did not get as green as normal until we had ample rain in July. It is far too early to say whether we’re on this same course, but it’s something for which we’re developing near real-time monitoring infrastructure.”

Spring showstoppers

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.

For Rollinson, nothing says spring like the magenta blooms of Eastern redbud trees, expected to bloom around the Arboretum’s Meadow Lake and Lake Marmo in mid-April to mid-May. “Redbuds have really neat, vibrant flowers that lie all along the branches, instead of just the tips,” she said.

Throughout the Arboretum’s East Woods, Rollinson recommends watching for spring blooms starting in late March. A range of ephemeral wildflowers like Dutchman’s breeches, spring beauty and white and yellow trout lily will mark the onset of spring. “As the name indicates, spring ephemerals emerge and bloom early, but then disappear by early summer when tree leaves fully emerge and there is stiffer competition for light and water,” Rollinson said. “That means you might only have a few days to a week to see these blooms in any given location. But small changes in topography can create different light, temperature and moisture conditions, resulting in various areas of the East Woods flowering weeks apart.”

The Arboretum is expected to resume its weekly Spring Bloom Report on the mortonarb.org website in mid- to late-March with information on the spring flowering underway.

When to prune trees

According to experts at the Arboretum’s Plant Clinic, which offers free tree and plant advice for the public, the best time to prune most trees in the Chicagoland region is from mid-February to early May, as they heal more efficiently during this period.

However, there are a few notable exceptions, said Plant Clinic Manager Spencer Campbell.

“We have traditionally recommended pruning oaks and elms between Oct. 15 and April 15 to avoid overlapping with bark beetles that spread diseases like oak wilt and Dutch elm disease,” Campbell said. “However, in years with warmer-than-average spring temperatures, these pests may become active earlier, making it necessary to stop pruning even before April 15. It’s best to plan your pruning for these species now, or you may need to wait until fall to complete it.”

Meanwhile, maples, walnuts, birches, beeches, hornbeams and yellowwood produce heavy sap flow when pruned in early spring. “While this ‘bleeding’ is not harmful, it can be avoided by waiting until after leaves have fully emerged later in the spring,” Campbell said.

Spring-flowering shrubs such as viburnums and lilacs should be pruned after their blooms fade and the flowers drop. Storm-damaged and dead branches always should be removed promptly to prevent hazards and encourage proper wound closure.

For more information, visit the Arboretum’s webpage about pruning trees. The Plant Clinic is available to provide tree pruning and other plant care advice by phone at 630-719-2424, email at plantclinic@mortonarb.org or walk-ins at the Arboretum (with paid admission).