What causes leaves to turn color in the fall? Shorter day lengths and cooler temperatures trigger the leaves to discontinue the production of chlorophyll, allowing other pigments to shine through. Sunny days stimulate the manufacture of carbohydrates and cool (40-45° F) nights allow the carbohydrates to break down into sugars. The more bright sunny days and cool nights we have, the more brilliant the autumn colors. Adequate rainfall is also necessary. In a dry summer and fall, the leaves turn brown instead of red or yellow.
We’ve had exactly that this fall–warm sunny days and cool nights and we are being rewarded with a spectacular show.
Carotenoids color pumpkins, carrots, corn, and sunflowers, and provide yellow and orange pigments to the leaves.
Anthocyanin give apples, cranberries, cardinals, and plums their red or red-violet coloring. These pigments develop in late summer in the sap of the cell as the breakdown of sugar begins. Unlike the carotenoids, anthocyanin varies from year to year, depending on the temperature and amount of sunshine.
Diane Ackerman The Natural History of the Senses
Ed Hedborn Fall Color
In my studio, my drawing table/desk is placed at right angles to the back window that overlooks the patio. Last week, I watched the Redbud and the towering Black Walnut change from just a few yellow leaves to overall dazzlingly bright and clear gold against the sunny blue sky.
Redbud (Cercis canadensis) , last mentioned in May to describe its exquisite bloom, is an understory tree, common in woodlands just south of Chicago, but rare to the north. Its large, heart-shaped leaves turn to a glorious gold early in the fall, as you can see here. A fast grower, Its spreading crown grows wider than tall, creating a delightful umbrella to sit under.
Black Walnut (Juglans nigra) has a bad reputation. Many think that the juglone produced by the roots is poisonous to all other plants, but that’s not true. Members of the rose family–rose, potentilla, spirea, chokeberry–and the nightshade family–tomatoes, eggplant–won’t grow within its root zone. In my experience, Witch Hazel (Hamemelis virginiana) and Wild Ginger (Asarum canadense) are not compatible either. But every other native plant that grows in woodlands will grow under a Black Walnut.
An open-grown Black Walnut is a magnificent tree–it can grow as tall as 100’ with an equal spread. The compound leaves turn a brilliant gold in October, as you can see here, a standout when viewed in relation to the deeply-furrowed, dark brown bark. The nuts are tasty with a unique flavor, but extremely difficult to crack open. Its fine-grained, dark brown wood is in demand for furniture and cabinet making–trees have literally been stolen from rural areas. In the wild it is found in upland savannas and in floodplains.
Don’t plant a lawn under it or build a patio or deck beneath it–it is incredibly messy when the nuts drop. If, however, you underplant it with native woodland sedges and wildflowers, the fallen nuts won’t be noticeable.
I live a few blocks south of Walnut Ave., and, as might be surmised, there are numerous Black Walnut trees in my neighborhood.
Blue-stemmed Goldenrod (Solidago caesia) on the other side of the patio, repeats the gold of the tree leaves. The 1-3’ stem arches prettily; its little golden flower tufts bloom from every leaf axil. It branches at the top and both leaves and blossoms become smaller and closer together.
This plant is always viewed from the top–its flowers face upward bordered by a fringe of leaves that hang down along the edge and give it its other common name–Wreath Goldenrod. In the garden, it grows in full or partial shade. In nature, it is found in woodland and sandy Black Oak savanna. Rare in Illinois, it’s common in Indiana.
As I finish this piece today, Sunday, I’m sitting on the patio and the big heart-shaped leaves of the Redbud begin to fall, while the smaller leaves of the Black Walnut rain down in the slight breeze.
O be less beautiful, or be less brief.
Sir William Watson
Serendipity:The faculty of making fortunate and unexpected discoveries by accident. The American Heritage Dictionary
That would never happen in a formal garden, but it happens all the time in an informal garden where one delights in plants that have found the perfect place to reside.
#1 In England, gardeners are advised to plant a clematis within a spring flowering tree; in effect the tree will seem to bloom twice–the tree’s own spring blossoms and then the blossoms from the entwined clematis later in the season. And here I have the same effect–the honeysuckle bloomed in June and now Short’s Aster has insinuated itself within the trellis for autumn bloom. Self-seeded Giant Purple Agastache and White Snakeroot bloom alongside the trellis, adding more interest.
#2 Virginia Creeper (Parthenocissus quinquefolia) climbs up a drainpipe near the back door.
I didn’t plant the Virginia Creeper–it was on my property when I moved here. A free spirit, it creeps, climbs, and cascades willy-nilly, where it will. In woods it will clamber 35’ up a tree, then turn to flame late in September, often the first sign of fall. It will grow horizontally along a fence, as well.
#3 Virginia Creeper and Riverbank Grape Vine (Vitis riparia) make a colorful swag on my neighbor’s clothesline.