In Minnesota, autumn offers a brilliant, fleeting transition between the sweltering days of summer and the long, cold nights of winter. For a few magical weeks each year, crisp air carries the scent of fallen leaves across the state, with maples ablaze with crimson and oaks radiating a golden hue. As both a scenic escape and a hub of horticultural research, the Arboretum offers the perfect vantage point to explore what makes Minnesota’s array of fall colors so dazzling and dynamic. So, why do leaves change color in the fall? And why are some years more spectacular than others?
Minnesota’s Autumn Palette
“Shorter days and cooler temperatures signal trees to prepare for winter by conserving energy and water,” explained Eli Sagor, Extension Forestry Specialist and Professor at the University of Minnesota’s Cloquet Forestry Center. And according to Jessica Savage, Associate Professor and Plant Physiologist at the University of Minnesota Duluth, this process leads chlorophyll, the culprit behind the green hue of deciduous plants, to break down. In many species, leaf color change is due to the loss of chlorophyll, which reveals colors that were previously masked by the green, such as yellow, brown or orange. Yellow and orange leaf colors come from carotenoid pigments, which are always present in leaves and break down more slowly than chlorophyll, said Laura Irish-Hanson, an Extension Horticulture Educator based at the Arboretum.
But some species accumulate anthocyanins, pigments that produce red or purplish hues. Their production depends on high sugar levels in the leaves, which are boosted by sunny, warm days and retained by cool nights that slow down sugar transport. This sugar buildup triggers anthocyanin formation. When this ideal weather combination occurs, trees are more likely to show vivid reds. Without it, red pigments may not develop.
According to Irish-Hanson, the two biggest factors influencing a tree’s autumn color scheme are shortening day length and declining temperatures. But the process begins long before the leaves start to change. “A warm, wet spring sets the stage for a brilliant fall,” said Sagor. Adequate rainfall throughout the summer, especially late in the season, keeps leaves healthy, supporting brighter yellows, oranges and reds.
Arboretum staff recommend a trip to the Farm at the Arb to view the rick red autumn foliage of the ‘Brandywine’ red maple trees, located along Peter C. Moe Drve and behind the Red Barn. Photo by Nick Kreevich
Climate change is already reshaping this delicate process, however. According to Brandon Miller, Assistant Professor of Horticultural Science and Curator of Plant Collections at the Arboretum, the unpredictable and extreme weather caused by climate change can delay and dull the intensity of fall leaf color. Sagor confirmed that warmer weather can delay the start of color changes, making leaves stay green longer, shortening the timing window for vibrant foliage, and dulling its intensity. Sagor also said drought-stressed trees often produce fewer pigments, even when a drought hits early in the growing season. On the other hand, he noted that excessive rainfall can cause early leaf drop or even kill sensitive species. Overly warm fall nights can also interfere with anthocyanin production, resulting in less vivid reds and purples. As a result, autumnal colors may arrive later, fade faster and lose some of their brilliance.
Still, nature keeps us on our toes. “Some plants may exhibit more intense color changes when stressed,” said Irish-Hanson. But the most reliable recipe for spectacular fall foliage remains the same: a healthy growing season followed by sunny days and crisp autumn nights.
Where to See the Show
Although maples, oaks and serviceberries certainly put on a show at the Arboretum, fall color isn’t just about the forest canopy. Shrubs add rich reds and purples to the landscape, with some showcasing vibrant stems as well as leaves. “Often trees get more attention, but sumac, dogwood and Virginia creeper are some of my favorites,” said Savage.
For a few standout specimens at the Arboretum, Irish-Hanson and Miller both recommend the ‘Brandywine’ red maples located near the Farm at the Arb and the colorful trees in the Oak and Nut Collection. Miller also called out the longstanding black tupelo trees in the Pillsbury Shade Tree Exhibit, known for their fiery red leaves, as a highlight. Arboretum staff also encourage visitors to explore the Ornamental Grass Collection in the fall, where color and texture combine to create an enchanted seasonal landscape.
The Arboretum’s Ornamental Grass Collection comes alive with color and texture in the fall. Photo by Natalia Ungashick
Although unpredictable weather makes it difficult to pinpoint when peak leaf color will strike, Miller said, “I recommend visitors follow the Arboretum on social media and subscribe to our communication channels to receive the most up-to-date information on the best times to visit.” Miller also highlighted the Minnesota DNR’s Fall Color Finder, which provides weekly updates on the progression of fall color throughout the state.
So on your next visit to the Arboretum this autumn, take a moment to observe and appreciate the science behind the ephemeral transformation of our trees.
Cover photo by Nick Kreevich
This story was originally published in Arboretum Magazine, a quarterly magazine for members of the University of Minnesota Landscape Arboretum.