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Drought and Fall Colors
by Yvonne Woulfe, Little Red Schoolhouse
October 21, 2012

The high temperatures and drought of the summer of 2012 set records and took a toll on the trees of northeastern Illinois. As a result, some trees suffered leaf scorch and dropped their leaves early.

Trees require enormous amounts of water to survive. A large tree absorbs about 95 gallons from the soil each day, or five bathtubs full of water. If you could look inside a tree on a hot summer day, you would observe water moving at a speed of three feet per minute up through the trunk.

Trees in garden landscapes should be kept well watered during hot, dry summers. Water once a week to a depth of several inches to keep the tree adequately hydrated. Check soil moisture by inserting a long screwdriver into the ground over several test areas around the tree. If the inserted screwdriver comes up dry, the tree is experiencing stress. Avoid watering too close to the trunk. Instead concentrate watering around the circumference of the tree to the drip line (edge of branches) to thoroughly hydrate outlying root systems.

Cottonwoods need the most water of local trees. They can be found growing in lowlands or along flood plains. There are 60 varieties of oaks in Illinois. Oaks are better adapted to survive drought conditions than other trees.

Yvonne brought leaf samples to pass around. Some showed evidence of leaf scorch. Maples were hit hard this summer because of high temperatures, high winds and drought. Damage showed up at tree tops as high branches died back. Root systems were also experiencing stress to match above ground damage.

Drab and disappointing fall colors were predicted as a consequence of the summer's stressful June, July and August. Then the September rains came, bringing cooler temperatures and drenching moisture. As September came to a close, trees began to put on their golden and crimson colors, almost overnight.

Trees turn color from the top down. Most of the world does not experience fall colors as we do in the Midwest. It is the shorter daylight hours and frost that trigger the autumnal display. Surprisingly enough, autumn begins for trees on June 21st when daylight and evening hours are equal. Then as daylight hours grow shorter and nights grow longer, there is less time for tress to absorb sunlight and synthesize energy. The preparation for fall and winter begins. At night, trees take in carbon dioxide and leaf production goes down.

By contrast, in spring, a green pigment called chlorophyll gives the leaf its color. During photosynthesis, chlorophyll captures energy from the sun to produce food sugars. In fall, as chlorophyll production drops off, the leaf loses green color. Depending on the tree species and the weather, most leaves turn yellow, orange, red or purple. As the growing season draws to a close, trees put their energy into next year's leaf buds.

Yvonne passed around sample branches of a variety of trees with their dried brown leaves still attached already showing well established leaf buds in place. .

The Midwestern hardwoods display some of the most brilliant and stunning colors to be seen anywhere in October. Leaves of sugar maples turn fiery orange and red. Basswood leaves turn butter yellow and are exceptionally brilliant and glowing when sunlight streams through their branches. But even on cloudy, rainy days, their golden leaves light up the woods. Oaks are the stalwarts of the autumn. Pin oaks are lovely in scarlet. The magentas of red oaks, the golden/browns of bur oaks and the wine colors of white oaks can last well into November. But even after the colors are over, some oaks hold their dried drab leaves into spring. They rustle in the wind and are sometimes frosted with snow, even as the buds of next year's leaves begin to swell beneath.

In conclusion, Yvonne passed around a bowl of about a dozen bumpy lime green fruits of the Osage orange tree. The gnarly wood of Osage orange is one of the hardest known. Osage orange trees were used by early settlers to mark property boundaries and were easier to maintain than wooden fences. Today, Osage orange trees can still be seen along country roads, their green fruits scattered on the ground beneath in fall. Yvonne told us that the Osage orange tree is one of the oldest on Earth. It was known to exist millions of years ago at the time when dinosaurs roamed the earth.

Photos by Valerie Spale

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