As autumn approaches, the Morton Arboretum in the Chicago region is keeping a close eye on weather patterns that could shape the timing and intensity of fall foliage. Senior forest ecologist Christy Rollinson, Ph.D., explained that the unusually strong El Niño this year is expected to bring warmer temperatures through October, November and December, potentially delaying the peak of color change.
Weather extremes and their effects
Rollinson noted that the summer saw a swing from severe drought to heavy rainfall, creating “high‑light and high‑stress environments” where some trees have already begun to turn. Early‑changing species such as the autumn blaze maple have shown color in late August and early September, but most maples typically reach their brightest hues in mid‑October, with oaks following in late October. In the Chicago area, leaves generally remain on trees through early to mid‑November.
El Niño’s role in the season
The warming influence of El Niño can compress the color window, causing many species to change simultaneously rather than gradually. Rollinson said, “If this holds, we expect El Niño to delay autumn color in general, but once we see several nights of freezing temperatures that leaves can’t survive for long, their colors will begin to change quickly.” Historical data show that warmer autumns tend to push back the onset of color, while daylight length remains a key cue for different species.
What visitors can expect
The Arboretum, home to nearly 4,100 plant varieties across 1,700 acres, will continue to update a weekly Fall Color Report on its website, helping guests track the progression of hues. The annual Fall Color Festival runs throughout October, offering family‑friendly events such as the Walking Plays series, a Cider and Ale Festival, the 16th annual Glass Pumpkin Patch, a new Autumn Reserve Wine Experience, Plant Bingo, and a 5K Run and Walk.
Additional programming includes Oak Awareness Month (OAKtober) with talks, guided walks, and a special “In Trees” conversation with author Robert Moor. Seasonal concessions featuring apple cider doughnuts, taffy apples, warm kettle corn, pretzels, chili, craft beers and other warm beverages will be available on weekends and on Indigenous Peoples’ Day, Oct. 12, in the Arbor Court area.
Looking ahead
While scientists acknowledge that the exact impact of El Niño on the timing of color change remains uncertain, the Arboretum’s monitoring efforts aim to provide both visitors and researchers with real‑time insight into how climate variability influences one of the region’s most beloved seasonal displays.
Original reporting: Positively Naperville (Aurora area) — read the source article.
