Regular readers of this column may recall the enthusiasm with which I embrace autumn. I just delight in the smell of wood fires at dusk; leaves turning and twirling on their way to the ground; and the chill in the air that urges us to start baking again and makes us reach for an extra blanket and add another log to the fire.
The same short days and cool temperatures that drive us to various acts of domesticity induce our gardens to get ready for the coming months as well, and as the trees prepare for their long winter’s nap, they put on a dazzling show.
All perennial plants, including trees, take precautions to help them survive the freezing temperatures and harsh winds of our long, cold northern winters. Some parts of a plant (stems, trunks, twigs) are equipped to survive these conditions, while other parts (tender leaves) are not.
Unlike evergreens, whose tough needles can withstand freezing, broadleaved plants and trees are not able to protect their leaves from the elements, so they lose them.
Preparations for this eventuality begin in early autumn, with the gradual closing off of veins bringing water and other nutrients into and out of the leaves. This affects the production of the pigment chlorophyll, which makes plants green.
Chlorophyll, essential to photosynthesis – the chemical process by which plants convert sunlight to food – is constantly produced and broken down during the growing season.
But the arrival of shorter days and chilly nights signals a tree to slow its manufacture of chlorophyll in advance of winter dormancy, and what remains in the leaf is eventually broken down, leaving other pigments that were always there to take center stage.
The reds, yellows, purples, and golds that dominate the autumn landscape are due to the presence of these other pigments found in leaf cells.
Carotenoids, the group of pigments that give daffodils, carrots, and bananas their yellow and orange colors, are revealed once the chlorophyll disappears.
No longer relegated to the shadows, they show up in the spectacular yellows and golds of the gingko, witch hazel, hickory and redbud in fall.
Anthocyanins, the red and purple pigments that color fruits we love, like strawberries, cranberries, red apples and plums, are produced by some plants in the fall as a result of bright light and high sugar content in leaves.
When present, these pigments can mask the yellows and result in the purples and fiery reds of some maples, oaks, serviceberry and dogwoods come October.
While there is no real way to accurately predict fall color, warm, sunny days, followed by cool, but not freezing, nights seem to result in the most spectacular displays.
The sunny days cause increased sugar production in the leaves, and the chilly nights and closing veins trap the sugars there, where they trigger anthocyanin production, making the reds more vibrant.
Soil moisture is also a factor in the brilliance of fall color, which means that inadequate rainfall during spring and summer can alter the timing and intensity of color change.
So, as we bustle about preserving peaches and canning tomatoes, unearthing flannels, and bringing out our warm woolen mittens this fall, the garden is hard at work, too, even if we can’t always see it. When we finally do, though, it’s magnificent.
• Sarah Marcheschi is a University of Illinois Extension Master Gardener for Kane County. Call the extension office at 630-584-6166 for more information.