Master Tips from a Master Gardener (11/16/17)

Bill Koellner · Wednesday, November 15, 2017
As you drive around the countryside in the fall, you are struck by the absolute beauty of beautiful fall leaves. Three sugar maple trees were planted on the entrance driveway at First Church United in honor of Pam Westra by her parents. These trees are a great, extra-reliable tree that makes a big statement in fall, sugar maple offers gorgeous red, orange, or yellow end-of-the-season leaves.

A wonderful shrub in several seasons, chokeberry offers white flowers that look like apple blossoms in spring; rich red fruits in late summer and autumn; and brilliant orange-red fall foliage.

Stewartia is a top-notch tree that looks beautiful throughout the year. Its dark green leaves make a nice foil for the late-summer, white camellia-shape flowers. In fall, the leaves turn festive shades of orange, yellow, and red.

Ginkgo is a slow-growing ginkgo that adds grace to the landscape; its fan-shaped leaves are among the most elegant of any tree. In autumn, they show breathtaking shades of luminous, golden-yellow. After the leaves drop, you'll be waiting for next fall.

Viburnum is a well-rounded shrub that offers beautiful clusters of white flowers in spring, then bright foliage in warm shades of red come autumn. Those eye-catching leaves are accented by ruby-red fruits.

Serviceberry is a plant for season-long beauty, we adore serviceberry for its display of white springtime flowers, delicious summer fruits, and amazing orange and red fall foliage. We have this bush in our yard, and recently have planted two at the north entrance of First Church.

If you want a plant that is unique, plant a Bald Cypress. Bald Cypress is a "fooled-you" plant come autumn; a bald cypress looks like an evergreen conifer. But in fall, the needles turn russet-red before dropping from the tree, revealing the tree's dramatic architectural shape that you can enjoy all winter.

Enjoy the Virginia Sweetspire for months. In summer, it offers fragrant white flowers. Then in autumn, it develops rich purple-red leaf color, plus, it's very easy to grow.

One of our favorite shrubs for shade, oakleaf hydrangea offers beautiful clusters of white blooms in summer, then wonderful burgundy fall foliage.

Sweet Birch is a beautiful tree, we love sweet birch for its cinnamon-colored peeling bark and triangular dark green leaves that turn beautiful golden-yellow in fall.

Smokebush is loved as much for its summer purple or gold foliage and plumes of soft, shimmery flowers, smokebush also offers great fall color --- often in bold shades of orange and pink.

Those of us who live near large timber areas have a visual seasonal barometer to tell us when spring and fall are arriving. The “barometer” is the splash of bright, virgin green in the spring tells us that warm weather is not far away, and the flash of brilliant colors in the early fall signals that cooler weather is on the way.

Why do leaves change color in the fall? Scientists have understood for a long time the reasons why leaves change their colors to yellow and orange in the fall. The pigment that causes the leaves to appear yellow is the same pigment that gives egg yolks their color, xanthophyll.

The orange color comes from a pigment, appropriately known as carotene, which gives carrots their color. These pigments are present in the leaves all summer long and assist in extracting the maximum energy from sunlight, but their colors are masked by the green pigment of chlorophyll. Think of chlorophyll as green paint on a brown or yellow surface. Chlorophyll is the component that allows plants to convert sunlight into the energy used to drive the chemical reactions they need to grow.

During the summer, chlorophyll continually deteriorates and needs to be constantly replaced, in effect “repainting” leaves with green pigment over and over again. But in the fall, as plants prepare to rest for the winter, chlorophyll production slows and finally stops.

As the green “paint” disappears, the yellow and orange shades underneath become visible. The red and purple colors are caused by other pigments called anthocyanins which, unlike the yellow and orange pigments, are not present all summer long but are synthesized in the leaves during the fall. The function of anthocyanins is controversial.

According to the traditional view, anthocyanins are created from sugars that are trapped in the leaves during the fall. Throughout the warm summer months, the sugars move throughout the plant to provide the energy for growth.

When nighttime temperatures drop in the fall, cells in an area called the abscission layer develop at the base of the leaves cutting off circulation to the leaves. Sugars still being produced in the leaves at this time accumulate there and chemically change into anthocyanins, giving the leaves their red and purple colors, or so the story goes.

Some scientists postulate that the anthocyanins are a form of sunscreen for the plant. Others believe they play a role in protecting the leaves from insects. According to yet another theory the anthocyanins are produced to protect the photosynthetic cells as the chlorophyll begins to break down in the cooler weather, thus prolonging their production of sugars and coloring the leaves.

Why are the colors more spectacular in some years than in others? And why are the fall colors in some areas more brilliant than in other areas? According to the US National Arboretum, weather conditions throughout the growing season and especially the fall influence the nature of the fall colors. The amount of sunlight and temperatures during the period when the abscission layer is forming at the base of the leaf petiole control the rate at which chlorophyll is destroyed. Cooler nighttime temperatures combined with abundant sunlight during the days promote the production of anthocyanins. The Arboretum states, “a growing season with ample moisture that is followed by a rather dry, cool, sunny autumn that is marked by warm days and cool but frostless nights provides the best weather conditions for development of the brightest fall colors.” But what about the second question? Why are some areas especially noted for producing brilliant fall colors?

Obviously the types and relative proportions of the different types of trees in an area is the most important variable, but even areas with similar types of trees may differ. Two scientists at the University of North Carolina-Charlotte, Emily Habink and Martha Eppes, suggested the answer in a presentation to the Geological Society of America.

Their explanation nicely dovetails with the sunscreen theory and provides a clue as to why some areas perennially have more brilliant fall colors than others. The authors of the presentation observed that nutrient-poor soils—especially soils low in nitrogen—cause trees to produce more anthocyanins and therefore display more brilliant colors.

Thus the production of anthocyanins would appear to be a survival mechanism designed to extract the maximum nutrition from poor soils as the temperatures drop and the trees prepare for the cold winter ahead.
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