by Lis Friemoth
Enjoy show while it lasts
Living in the northern part of the United States is always interesting. The winters are cold, and if we’re lucky, full of snow; spring is often cool, wet and muddy; summers are oh so hot and muggy; but the autumns, ah, the autumns are glorious.
The colors, the nutty scent to the air, the end of lawn mowing — all are good reasons to get out of bed in the morning.
It’s the time of year to walk, to ponder, to plan for making up lost time or completing forgotten tasks. Oh, let’s be honest; on a glorious fall day, the work can wait. Go for a walk and look at the colors.
Did you ever wonder where the colors come from and why they vary year to year? Although science has a good handle on some of the factors affecting the color-change process in leaves, there are still components out there that are not well completely. We do know that leaf color depends primarily on the factors of heredity working in conjunction with environmental conditions, like air temperatures, water, sunlight and composition of the soil.
Let’s start with what to expect out of tree species. Each species and its heredity play a huge role in what pigments are present in the leaves and what colors they show in the fall. Most — but not all — trees will exhibit fall color in shades from within one palette.
Trees in the Acer family (maple) nicely represent the bright reds; Betula family (birch, poplar) turn yellow; Carya (hickory) and Corylus (hazelnut) will both burnish to a nice golden brown; Cornus (dogwood) leaves are reliably reddish-purple; Fagus (beech) are light brown; Quercus (oak) range between brown and red; and Sumac gives us those beautiful and very brilliant reds. (OK, this one is a shrub but it’s so pretty!)
There are a handful of other shrubs that will produce multiple colors on each leaf. Fothergilla and Disanthus are two to consider adding to the landscape.
Normally, during the growing season when day and evening temperatures are warm, sugars and proteins move freely from the leaves to the rest of the tree system. As evenings cool and daylight lessens, the leaves begin the process of closing off the veins in the area between the leaf stem and the tree branch, as preparation for leaf drop. Nutrient production declines and as the veins close, excess sugars and protein are trapped in the leaf tissue. This results in a lesser amount of green and an increased visibility of those comforting yellows, browns, and oranges or invigorating purples and reds. And boy, is this leaf coloration interesting to look at.
There are three main pigments present in leaves at various times of the growing season: chlorophyll, carotene, and anthocyanin. The colors that show as visible to our eyes are the result of the combination of these pigments and the reflected and absorbed light.
Chlorophyll is produced during the growing season through sunlight interacting with the carbon dioxide and water in the leaf tissue. This pigment absorbs blue and red light, showing green in the sunlight in such large amounts that it masks the underlying leaf pigments.
Carotene absorbs blue and blue-green light, reflecting as a yellow color later in the growing season (after the production of chlorophyll has begun to reduce). Carotene pigment will be present in leaf tissue throughout the growing season but may be masked by the chlorophyll or enhanced during the late-season anthocyanin.
Anthocyanin is the third pigment present and is produced from the excess sugars and proteins in the leaf tissue. This pigment absorbs blue, blue-green, and green light, meaning that the remaining visible color (after chlorophyll production ceases) will be red or purple depending on the leaf sap pH. A high pH will result in purple colors; low pH results in reds.
When trying to gauge how much color will be visible (given the species limitations), we look at air temperatures, soil moisture, and overall tree health at various times of the year.
For optimal colors, a slightly health-stressed tree, a wet spring, moderately moist summer, and a dry, sunny fall are about perfect for optimal leaf viewing. So what did we have?
Plenty of environmental stressors, not much moisture in the spring, too much rain for a time during the summer, and a fall that appears to be going nicely so far. We are already seeing some early leaf drop as a result of the water and temperature extremes throughout the growing season — and that wicked early frost didn’t help either.
Honestly, the weather conditions are not textbook for the most optimal color show, but really, when has a tree read a book? No matter the conditions leading up to fall, our woodlands provide such a varied and beautiful show every year, that it would be a shame to miss any of it.
— Lis Friemoth is a horticulture diagnostician. Contact her at (262) 745-2904, P.O. Box 58, Springfield, WI 53176, visit online at www.thegardenhoe.com or e-mail her at gardenhoe@tds.net. Listen to Liz from 9 a.m. to 10 a.m. every third Saturday on WISN AM1130 radio. |
