Most East Texans take fall color for granted. I’ll admit that we aren’t New England, but having lived in San Antonio, College Station and Dallas where brown leaves are the norm, we are very blessed when it comes to autumn foliage.
As the days get cooler and frost is in the air, deciduous trees like blackgums, maples, sassafras, sweetgums and sumac put on an autumn show in all shades of yellow, orange, red and purple. In many parts of the country, autumn leaves are an important factor in tourism. I think they should be here as well, since our neighbors to the west are starved for fall color.
Many think that cool weather or frost causes the leaves to change color. While temperature may dictate the color and its intensity, it is only one of many environmental factors that play a part in painting deciduous trees in beautiful fall colors. To understand the whole process, it is important to understand the growth cycle of deciduous trees. During the growing season, trees store up carbohydrates to support next year’s growth.
The process that starts the cascade of events that result in fall color begins in late summer or early autumn when the days begin to get shorter and nights are longer. When nights reach a certain length, the cells near the leaf petiole form an abscission layer and slowly begin to block the transport of carbohydrates from the leaf to the branch.
During the growing season, chlorophyll is replaced constantly in the leaves. Chlorophyll breaks down with exposure to light, so the leaves must constantly manufacture new chlorophyll to replace that lost. In autumn, when the connection between the leaf and the rest of the plant begins to be blocked off, the production of chlorophyll slows and then stops. In a relatively short time period, the chlorophyll disappears completely.
This is when autumn colors are revealed. Chlorophyll normally masks the yellow pigments known as xanthophylls and the orange pigments called carotenoids. Both then become visible when the green chlorophyll is gone. These colors are present in the leaf throughout the growing season. Red and purple pigments come from anthocyanins. In the fall, anthocyanins are manufactured from the sugars that are trapped in the leaf. Some years more are produced and in some years less.
Temperature, sunlight and soil moisture greatly influence the quality of the fall foliage display. A growing season with ample moisture that is followed by a rather dry, cool, sunny autumn marked by warm days and cool frostless nights provides the best weather conditions for development of the brightest fall colors. Early hard freezes, heavy rain and high wind can put an end to the party. Naturally there’s no guarantee to what we will get. But the unexpected, fleeting beauty of it all is part of its magic.
MASTER GARDENER ORIENTATION THURSDAY
If you’d like to learn more about colorful plants and horticulture in general, consider becoming a member of our Smith County Master Gardener volunteer team. We are having an orientation from 1 to 3 p.m. Thursday for those who are interested in applying, in Room 116 of the Cotton Belt Building. For more information, call 903-590-2980.
Greg Grant is the Smith County horticulturist with the Texas A&M AgriLife Extension Service. You can follow him on Facebook at “Greg Grant Gardens.” He writes a monthly blog titled “Greg’s Ramblings” at arborgate.com and writes “In Greg’s Garden” for Texas Gardener magazine (texasgardener.com).