“In the garden the superb color effects from August to November make autumn the crowning glory of the year.” I could not agree more with Rose G. Kingsley, The Autumn Garden, 1905. In our eastern area of North America, it is truly an awesome sight when the foliage from countless deciduous trees, shrubs, and vines dramatically change from a consistent green to vivid yellows, fiery reds, or glowing oranges. This phenomenon is actually quite rare occurring in only three regions of the world: sections of Eastern Asia in China and Japan; a small part of Central South America; and, lucky for us, a large portion of North America. Each area is splendid and unique baring a color intensity, scale, or length of season that significantly varies. Undoubtedly, the most brilliant colors are found in North America’s deciduous forests enchanting artists or tourists alike in hues of orange, purple, yellow, or red. To catch a glimpse of autumn splendor many people travel to the states along the Appalachian Mountain chain or to other prominent mountain destinations. So, you might wonder: What makes leaves that had been green on the trees for so many months change so dramatically?
Leaves turn color and eventually drop in response to a number of factors working together. These include moisture, day length, temperature and sometimes even the plant species. The shortening length of daylight is what initiates biochemical changes within a leaf. Three primary pigments, chlorophyll, carotene, and anthocyanin are all present in the leaf as it gathers sunlight producing the sugars needed by the plant for food. Chlorophyll makes the leaf appear green while masking the two other pigments. It can only be manufactured when day length is longer and the weather is warm. Carotenes are yellow pigments that help protect the leaf from the by-products of photosynthesis. Anthocyanins are red pigments that act like a sunscreen protecting the leaf from sunlight. As the weather cools, plants stop producing chlorophyll as a corky layer develops at the base of the leaf stalks. Then masked carotene and anthocyanin pigments increase in intensity. This coloring process is similar to the changes that occur with ripening fruit. For example, carotene gives orange color to a pumpkin or transforms a ginkgo tree or summer sweet shrub into a bright yellow. Anthocyanin gives red color to apples or strawberries besides producing the bright scarlets and purples of Japanese maple (Acer palmatum), burning bush (Euonymus alata), or Boston Ivy (Parthenocissus tricuspadata). Different plant species can cause fluctuations in the timing for color change. For instance, Black gum begins to show brilliant scarlet branches in late August; dogwood turns into red by mid-September. Maples become red and orange in late September and early October. Since no two autumns are exactly alike, even plants best known for their outstanding fall color, can differ in intensity from year to year. The weather and growing conditions are what impacts the color intensity most and how long it will last. A succession of warm, sunny days with cool, crisp above freezing nights seems to bring about the most spectacular color displays. But, conditions such as these will affect the spectacle: An early killing frost can wither leaves before they color; strong winds may blow them away; very warm autumn temperatures or severe drought stress can accelerate color change and leaf drop; soil that is too wet works the opposite way by delaying color development. In many locations drought is quite common. In fact, moderate drought actually intensifies the quality of fall leaf colors while too much drought can hasten leaf browning, causing them to fall earlier than usual. In most years, Northern PA counties reach their best autumn color October 1-10. Now, let’s enjoy the show before we “fall back.”