Tag Archives: fall color

The Mysteries of Fall Color

In case you were wondering…
Every autumn in Illinois brings with it a breathtaking change of color in the leaves of our trees, but although it’s late September, temperatures have been steadily topping out in the nineties every day.  Not a traditional sign of Fall, yet the trees are changing color and dropping leaves as if they were not aware of the hot and humid weather.
Aren’t the leaves supposed to change when it gets cooler and we see some frosts overnight?
Do the trees know what time of year it is despite the unusually warm temperatures?
One explanation, according to Native American myth, is that the hunters in the Heavens killed the Great Bear in autumn and its blood dripped over Earth’s forests coloring some of the leaves red.  As the hunters cooked the meat, fat dripped from the Heavens and colored some of the leaves yellow.
Not scientific enough for you? Need a more botanical answer?
In case you were wondering what actually initiates the changing color of the leaves and their eventual fall to the ground, read on…
Most people think that cool weather or frost causes the leaves to change color. It is true that there is usually a correlation between the cooler air and the onset of the autumn show.  However, while temperature may impact the color intensity, it has less impact on the timing of the color transitions we see in the Fall than do other factors.
A quick trip back to high school Botany 101.  During the spring and summer most of the foods necessary for the tree’s growth are manufactured in the leaves.  This food-making process takes place in the numerous cells containing chlorophyll, which gives the leaf its green color. This extraordinary chemical absorbs the energy from sunlight that is used in photosynthesis, the transformation of carbon dioxide and water to carbohydrates, such as sugars and starch.
In late summer or early autumn, the days begin to get shorter, and consequently, the nights are longer. Like most plants, deciduous trees and shrubs are rather sensitive to the length of the dark period each 24-hour cycle. When nights get long enough, the cells of the leaves begin to block transport of materials such as carbohydrates from the leaf to the branch. They also block the flow of minerals from the roots into the leaves. Because the starting time of the whole process is dependent on night length, fall colors appear at about the same time each year in a given location, whether temperatures are cooler or warmer than normal.
The fact is, the vivid yellow and orange colors have actually been there throughout the spring and summer, but we haven’t been able to see them. The deep green color of the chlorophyll, which helps plants absorb life-giving sunlight, hides the other colors.  In the fall, fewer hours and less intense daylight prompt the leaves to stop the food-making process. The chlorophyll breaks down, the green color disappears, and the yellow and orange colors already in the leaf become visible again to the human eye.  As the trees break down the green pigments and nutrients stored in the leaves they are shuttled into the roots for reuse in the spring.
Along with the green pigment of chlorophyll are carotenoids, yellow to orange pigments, which, for example, give the orange color to a carrot. At the same time other chemical changes may occur which produce red anthocyanin pigments resulting in even more variation in the Fall color scheme.  Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange. For most of the growing season these colors are masked by the great amounts of green coloring.
The variations in Fall color are due to the mixing of varying amounts of chlorophyll residue and the other pigments in the leaf combined with a varied response to weather conditions. For instance, as the nights become cooler, the sugars trapped in the leaves of some oaks and maples will often form a red pigment.  The degree of color will also vary from tree to tree.  Leaves directly exposed to the sun may turn red, while those on the shady side of the same tree or other trees may be yellow.
As the fall colors appear, other changes are taking place. At the point where the stem of the leaf is attached to the tree, a special layer of cells develops and gradually severs the tissues that support the leaf. At the same time, the tree seals the cut, so that when the leaf is finally blown off by the wind or falls from its own weight, it leaves behind a leaf scar. Most of the broad-leaved trees in Illinois shed their leaves in the fall. However, the dead brown leaves of the oaks and a few other species may stay on the tree until growth starts again in the spring.
In general, autumn weather conditions favoring the most brilliant colors are warm sunny days and cool, but not freezing, nights. When there is mainly warm, cloudy and rainy weather in the fall, the leaves may have less red coloration.  A few hard frosts can cause the leaves to wither more quickly and drop to the ground.
So, in case you were wondering, with all due respect to the Native American myths, it is a combination of temperature, light, and water supply that have an influence on the onset, the degree, and the duration of fall color.
Enjoy it while you can, because it doesn’t last long!

Favorite plant series: Amsonia tabernaemontana ‘Blue Ice’

During a meeting discussing seasonal color displays, when phones were set on vibrate and the focus of our discussions was solely about plants, I was reminded how passionate and opinionated our staff is when it comes to what they love the most.

I decided it was important to celebrate that our employees each have their favorite species and that those favorites tend to change and evolve.  Hence our favorite plant series.  First up might as well be me, Donna Vignocchi Zych.

Easy and carefree, ‘Blue Star’ is an outstanding long blooming selection. I look forward to several weeks of deep, glacial blue blooms on this compact, shrubby-like plant. It forms a mound of green, willow-like leaves, bearing clusters of interesting dark blue buds that open into dainty, star-shaped, medium blue flowers from late spring into early summer. The dark green, compact foliage remains attractive all summer and forms the perfect backdrop, for colorful annuals and bold perennials. In fall, the willowy foliage turns a rich shade of yellow complementing my favorite fall blooming perennials: sedum, hardy mums and purpled-leaved heuchera, to name a few.

Light: Full sun to part shade

Soil: Well-Drained

Height: 12-18”

Spread: 12-18”

Growth Habit: Dense, Mound, Shrub-like

Uses: Specimen, edging, or massed in perennial or mixed shrub borders

Problems: No serious insect or disease problems.

Companion Plants: Sedum, Allium, Blue Hosta, Purple-leaved Heucheras

Dark blue buds open to ice blue blooms

Dark blue buds open to ice blue blooms

Amsonia spring blooms

Spring blooms and neat dark green foliage

Amsonia fall foliage

Dark green foliage turns to golden yellow in fall


Geranium ‘Rozanne’

Tried and Trouble-free!

Year-after-year, ‘Rozanne’ continues to be a “rock star” in my garden!

I highly recommended ‘Rozanne’ for larger flowers than others of its type along with an extended bloom period and vigorous, yet dense, habit. The lovely saucer-shaped flowers are deep violet-blue with a white throat and darker venation. Attractive, faintly marbled, deep green leaves change to a brownish red in late fall for added interest. With a semi-vining habit, ‘Rozanne’ weaves gracefully through my garden, filling in any gaps along the way, allowing for its companion plants (see below) to flow together in a stunning blend of colors and textures.The non-stop show begins in June and lasts till frost.

Light: Full Sun to Part Shade

Soil: Well-Drained

Height: 1 to 3 ft.

Spread: 1 to 3 ft.

Growth Habit: Clumps, Spreads

Uses: Perennial beds, borders, also excellent for massing or in mixed containers.

Companion Plants: Coreopsis, Asclepias, Calamintha, Salvia, to name a few.  For more information about other fun geraniums, click here.

Semi-vining habit

Semi-vining habit

Close up of flower

Close up of flower

Fall color

Fall color


Why Leaves Change Color

fall maple

During the growing season, chlorophyll, essential for photosynthesis, is continually being produced and broken down and leaves appear green. As night length increases in the autumn, chlorophyll production slows down and then stops and eventually all the chlorophyll is destroyed. The carotenoids (responsible for orange, yellows and browns in things like bananas and clementines) and anthocyanins (responsible for reds and purples in items like cherries and berries) that are present in the leaf are then unmasked and show their colors.

Both chlorophyll and carotenoids are present in the chloroplasts of leaf cells throughout the growing season. Most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells.

A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions-lots of sugar and lots of light-spur production of the brilliant anthocyanin pigments, which tint reds, purples, and crimson. Because carotenoids are always present in leaves, the yellow and gold colors remain fairly constant from year to year.

The amount of moisture in the soil also affects autumn colors. A late spring, or a severe summer drought, can delay the onset of fall color by a few weeks. A warm period during fall will also lower the intensity of autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors.

Some of my favorite places to enjoy the onslaught of fall color?  Visit now and often over the next few weeks and watch the marvelous display.

Independence Grove (shown in photo above)

The Morton Arboretum