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Press Release: Understanding the science of spring

When plants will reach their peak bloom varies year to year, depending on the weather

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LISLE, Ill. (March 28, 2023) — Longer days, warmer weather and flowers in bloom mean more time spent outdoors enjoying the natural world. But knowing when plants will reach their peak bloom varies year to year, depending on the weather, according to scientists at The Morton Arboretum.

“Right now, we’re on track for earlier spring bloom times than is typical for the Chicago region,” said Christy Rollinson, Ph.D., forest ecologist at the Arboretum. “We’re entering a critical window where a couple of warm or cold days could create the difference between a truly early bloom season or not.” She added that spring leaf-out is being reported as weeks early for central Illinois, Indiana and Ohio—and in many cases, the earliest on record in those areas.

Because the Arboretum has such a rich diversity of trees and plants across its 1,700 acres, it is a unique place to experience showstopping springtime blooms throughout the season. “Various species of trees and plants bloom at different points in the spring season, so while you may not see blooms in one area, others may already be showing colors,” Rollinson said.

To help Arboretum visitors know what to expect as they explore, the outdoor tree museum publishes a weekly Spring Bloom Report from early March through mid-June, which also gives clues to what may be blooming around the region.

The timing of a particular plant’s blooms can vary by weeks from year to year, in response to the weather, Rollinson explained. For example, Arboretum records show that in 2012—when it was extremely warm early in the spring—daffodils were all in bloom by March 22. Despite some blooms’ possible early arrival this year, daffodils are not expected to flower for another week or so.

Rollinson said that trees and other plants know spring has arrived through a combination of signals—day length, warm temperatures, sunlight and moisture—that trigger hormones and cause changes to occur, such as green sprouts poking up from seeds, buds swelling and, eventually, flowers opening. “Every spring is a different experience for plants since the triggering factors can change every year and even every day during the season,” Rollinson said. “Even plants of the same species may not bloom at the same time if they’re in different locations.”

So, when’s the best time to visit the Arboretum to see the most blooms? “Whenever you can,” Rollinson said. “There’s always something different blooming along the trails and in the gardens, and it’s always beautiful.”

Spring Showstoppers

While the exact timing of spring blooms may be a challenge to precisely predict, here’s a list of what Rollinson suggests to watch for at the Arboretum as spring progresses in the Chicagoland region.

  • Mid-season blooms (usually April) will include various spring wildflowers found in the East Woods, the popular daffodils (Narcissus) in Daffodil Glade, and redbuds (Cercis canadensis) lining the edges of Lake Marmo. It will be the first spring in The Grand Garden, and the Centennial Plaza display promises to be fragrant and showy beginning in mid-April, and will include a mixture of pink and purple tulips, pink muscari and yellow hyacinths.
  • Late-season blooms (usually May) include the must-see Crabapple and Magnolia Collections, which are accredited by the American Public Garden Association’s Plant Collection Network.

Guided Tours

To see the best of spring at the Arboretum, leave the wayfinding to the naturalists during guided spring hikes for all ages.

Enjoy the ephemeral beauty of the season during family-paced Woodland Family Hikes, featuring Trees in Bloom on April 29 and May 6, and Spring Wildflowers on May 20 or 27.

Join two scientific researchers for Spring Flowering Trees Walking Tour on April 28 or May 6 as they discuss the seasonal changes of trees and what the timing of spring buds, leaves and blooms can tell us about the bigger picture of climate and the local environment.

For more information about Arboretum programs and special events, visit