fall color – My Chicago Botanic Garden

How a Heat Wave Can Affect Fall Color

When early fall feels like summer, that will going to change how long trees will show off their seasonal colors.

Deciduous trees, explains Boyce Tankersley, director of living plant documentation, respond to environmental conditions when preparing to go dormant for the winter. Just like animals that hibernate, trees slow their processes down in order to conserve energy. What we can see of this process can be beautiful: leaves change from green to vibrant reds, oranges and yellows. Then trees will drop their leaves and wait out the winter.

In a regular year, trees aren’t in a rush to go dormant. The process that we see takes several weeks. The production of chlorophyll, which produces the green color in leaves, fades away, unmasking the beautiful colors we associate with autumn. As the season progresses, the leaves will eventually drop. In Chicago, our trees usually reach peak color in the first two weeks of October, and aren’t usually bare until late October or early November.

But this isn’t a regular year. The heat we’ve been feeling lately is a factor.

Fall leaf color — Expect color, but this year’s display will be shorter than usual.

“The higher the temperature, the faster the processes go,” Tankersley said. And this month’s drought is why we’re also seeing leaves dropping only a few days into fall. Local rain gauges have been virtually dry, with less than 2 inches recorded in the month of September.

“Trees don’t have minds, but they do respond to environmental clues. If there’s been little rain, they will drop their leaves early in order to conserve water and get through the rest of fall and winter,” he said.

If you’re a fan of getting family portraits done with a backdrop of colorful foliage, Tankersley suggests getting those done sooner rather than later.

“This year, we’re going to have to be a little bit more proactive about getting out there and getting photos as the trees come into color. They’re just not going to hold.”

Autumn Scents

“What’s that smell?”

It’s what I’ve been asking myself in recent weeks. Not in a bad way; it’s an entrancing scent that’s been wafting through the air, at the Garden and in gardens I walk by in my neighborhood—but one I couldn’t quite place. I’ve been walking around, nose in the air, happy but perplexed.

Every spring we marvel at the sweet smells in the air. But perfumed breezes in autumn? And what an unusual perfume. Cilantro? With a hint of honey? What could it be?

“You’re smelling something that’s reminiscent of coriander, maybe cilantro?” said Jacob Burns, the Garden’s curator of herbaceous perennial plants. “You’re probably smelling Sporobolus heterolepis. Prairie dropseed.”

Welcome to a signature scent of late summer and early fall: the scent of prairie dropseed, a native grass.

PHOTO: A single panicle of prairie dropseed. — A single panicle of prairie dropseed

Prairie dropseed (Sporobolus heterolepis) — Prairie dropseed (*Sporobolus heterolepis*)

Never mind the sweet scents of spring; this season’s plant aroma is in a class of its own. And it’s almost indescribable. I thought of cilantro partly because of the scent, but also because I couldn’t quite place it or compare it to anything else—like cilantro.

“Some people think it smells like buttered popcorn,” said Garden horticulturist Liz Rex, who cares for the Native Plant Garden.

The scent comes from the flowers, feathery panicles that bloom in late summer. I’ve smelled it walking by gardens where people have planted a few native prairie species.

Rex has been surrounded by it in places where it is planted en masse.

“The first year I was in the Native Plant Garden, it was almost overwhelming,” she said. “But now I really enjoy it and look forward to it.”

You can smell it in various spots in the Garden, Rex said—the Native Plant Garden, the restored prairie, the Kleinman Family Cove near the new Regenstein Learning Campus, the Regenstein Fruit & Vegetable Garden; and the rainwater glen outside the Daniel F. and Ada L. Rice Plant Conservation Science Center.

You can smell it in remnant prairies, said Joan O’Shaughnessy, prairie and river ecologist at the Garden—and if you do, that means the prairie is of high quality.

But you can also smell it in ordinary gardens. Native species are increasingly popular in front and back yards, and prairie dropseed (it gets its common name because of the way its mature seeds drop to the ground in autumn) is a Chicago-area superstar.

“It’s a wonderful garden plant because its growth form is low, which people like; it has this fountain-like look to the vegetation; and you can keep it over winter for appeal,” O’Shaughnessy said.

It can grow in both wettish and dry soil. Like many native plants of this region, it can tolerate drought. It can grow in that bane of the Chicago gardener’s existence, heavy clay soil. “It’s just a great plant,” she said.

It isn’t the only source of fall fragrance in the Garden. There is also the katsura tree (Cercidiphyllum japonicum).

PHOTO: In early fall, the gold outline of katsura tree leaves is particularly visible as they begin to change color. — In early fall, the gold outline of katsura tree leaves is particularly visible as they begin to change color.

PHOTO: The late fall foliage of the katsura tree. — The late fall foliage of the katsura tree
Photo by Amy Campion

“The leaves turn a really pretty fall yellow, and once they drop, they release a sugary aroma that smells like cotton candy,” Burns said. “Some liken it to caramel or even brown sugar.”

You can find a katsura on Evening Island by the trellis bridge, he said, and also in the Krasberg Rose Garden.

So while fall’s colors are rightfully beloved, it turns out that the season appeals to another sense, too. Go ahead and enjoy looking at the annual show of autumn colors—but don’t forget the autumn scents.

5 Perennials for Spectacular Fall Color

As fall approaches and the leaves begin to change, the Chicago Botanic Garden bids adieu to our beautiful summer blooms until next year. The air starts to get crisper (and your summer plants will too), but September isn’t the expiration date for color and excitement at the Chicago Botanic Garden—and it shouldn’t be in your garden either.

We asked Tim Pollak, outdoor floriculturist, and Cindy Baker, manager of horticultural services, for their favorite fall-blooming perennials that will make your landscape pop this season.

PHOTO: Phlox paniculata 'Barfourteen' Purple Flame® garden phlox. — Purple Flame® garden phlox *(Phlox paniculata* ‘Barfourteen’)

Phlox paniculata
Garden phlox

Look no further for a long-blooming and beautiful native perennial that provides a whole palette of color options for your garden. Phlox cultivars add shades of showy pink, lavender, or white in clusters of delicate-looking flowers. Their sweet fragrance will attract late-season butterflies and hummingbirds to your own backyard. Garden phlox are generally hardy plants and will grow well in sun or shade. Plant in midspring with a layer of mulch to retain soil moisture for maximum flower production.

PHOTO: Panicum virgatum 'Dallas Blues' switchgrass. — Switchgrass *(Panicum virgatum* ‘Dallas Blues’)

Panicum sp.
Switchgrass

Ornamental grasses may not seem like an obvious choice for garden excitement but they can help to create texture and movement. Switchgrasses are an environmentally smart choice as they are native to tallgrass prairies in the United States. Cultivars are variable in color with red to light golden blooms and deep green to blue blades. Switchgrasses are low maintenance and will tolerate nutrient-poor soils, but plant in full sun to keep plants upright and blooming all fall. Because they can grow up to 8 feet in height, consider planting toward the back of your beds and place smaller plants in front.

PHOTO: Callicarpa japonica 'Leucocarpa' (Japanese beautyberry). — Japanese beautyberry *(Callicarpa japonica* ‘Leucocarpa’)

Callicarpa sp.
Beautyberry

This small shrub has something to offer year-round; it blooms in the summer, then its flowers are replaced by small berries that last until winter. Depending on the species, Callicarpa can have shiny white or bright purple berries—both are a big hit with birds. All species have long, arching branches that cascade outward but with pruning, the shape is variable. Beautyberry should be planted in rich soil and pruned in early spring but otherwise requires little attention throughout the year. Ensure your shrub receives adequate moisture for maximum fruit production all fall long.

PHOTO: Rudbeckia hirta 'Autumn Colors'. — Black-eyed Susan *(Rudbeckia hirta* ‘Autumn Colors’)

Rudbeckia cultivars
Black-eyed Susans and coneflowers

With familiar daisy-like flowers that will bloom through all of fall, it is no wonder that species of Rudbeckia are a fall favorite. Petal colors can range from shades of bright yellow to orange-gold, and some cultivars have flushes of red on the petals. Rudbeckia will respond well to deadheading or alternatively, leave the dried flower heads on the plant to attract migrating birds to your garden. This will also allow the flowers to reseed because not all cultivars of Rudbeckia will act as perennials in colder climates. These flowers are low maintenance if planted in well-drained soil.

PHOTO: Imperata cylindrica 'Rubra', or Japanese blood grass. — Japanese blood grass *(Imperata cylindrica* ‘Rubra’)
Photo by Jim Hood, via Wikimedia Commons

Imperata cylindrica ‘Rubra’
Japanese blood grass

Japanese blood grass is another low maintenance ornamental grass. Usually smaller in stature than switchgrass, it introduces a dramatic splash of deep red into your landscape. Although nonnative and normally a fiercely invasive plant, this cultivar does not produce seed and spreads slowly. This grass is best used as a border plant in well-drained soils.

Color the leaves to understand the shades of fall

Fall is a wonderful time to take a guided or self-field trip to the Chicago Botanic Garden. Children will love to learn about the many shades of fall leaves.

During the summer, tree leaves produce all the pigments we see in fall, but they make so much chlorophyll that the green masks the underlying reds, oranges, and yellows.

In fall, days get shorter and cooler, and trees stop producing chlorophyll. As a result, the green color fades, revealing the vibrant colors we love. Eventually, these colors also fade, and the leaves turn brown, wither, and drop. Then the trees become dormant for winter.

Download a coloring activity.

There are four pigments responsible for leaf colors:

Chlorophyll (pronounced KLOR-a-fill) – green
Xanthophyll (pronounced ZAN-tho-fill) – yellow
Carotene (pronounced CARE-a-teen) – gold, orange
Anthocyanin (pronounced an-tho-SIGH-a-nin) – red, violet, can also be bluish

Leaves are brown when there are no more photo-sensitive pigments; only the tannins are left.

Color these leaves according to the pigments they produce:

Honey locust

Leaves turn color early in the season; the lighter carotenes glow warmly against the blue sky and green grass.

Sugar maple

The fading chlorophyll, combined with xanthophyll, carotene, and anthocyanin, produce the spectacular show we anticipate every year. Leaves change slowly and over time may be any combination of the four pigments, ending in a brilliant flame of anthocyanin.

Japanese maple

The darker anthocyanin hues turn these feathery leaves the color of shadows—fitting for the spooky month of Halloween.

Sweetgum

Like the maple, this tree puts on an awe-inspiring display of xanthophyll, carotene, and anthocyanin all together.

Ginkgo

Light filtering through the xanthophyll and lighter carotene of these leaves creates an ethereal glow. The ginkgo drops all of its leaves in a day or two.

Sumac

The anthocyanin in these leaves makes them the color and shape of flames, and appears as fire against the duller colors of the surrounding landscape.

Buckeye

Carotenes recede quickly around the edges of the leaves as they prepare to parachute to the ground.

Tulip tree

A pale hint of chlorophyll mixes with xanthophyll and a touch of carotene as this tree shuts down for winter.

Pin oak

This stately tree holds its anthocyanin-rich leaves through the fall. The color eventually fades, but the tree holds its pigment-less leaves through the winter.

Download a coloring activity.

Facts about fall leaf colors:

Trees use the sugars they produce through photosynthesis to make all of the pigments we see.
The best fall color display comes in years when there has been a warm, wet spring; a summer without drought or excessive heat; and a fall with warm, sunny days and cool nights.
Chlorophyll, carotene, xanthophyll, and anthocyanin are also responsible for the coloring of all fruits and vegetables, including corn, pumpkins, beans, peppers, tomatoes, and berries.
Peak fall color comes earlier in northern latitudes than southern latitudes, so if you miss the best of the sugar maples in Chicago, take a trip south to get your color fix.
You can preserve a leaf by ironing it between sheets of wax paper.

Fall color(ing) activity correct colors:

Fall Color Infographic

If days stay cool and sunny, fall color will continue, peaking this next week. Here’s how it works:

Want to share our infographic? Download a print version here.