Garden Column for the Salisbury Post Darrell Blackwelder October 20, 2005      "Autumn is a second spring when every leaf is a flower" an eloquent quote from the French novelist and Nobel Prize winner Albert Camus eloquently describes the burst of fall color that will soon be upon us. It is often assumed that colder fall temperatures are responsible for leaf color; however the change in coloring is often the result of chemical processes which take place in the tree as the season changes.      During the summer leaves have served as factories where most of the foods necessary for the trees' growth are manufactured. Along with the green pigment leaves also contain yellow or orange carotenoids which, for example, give the carrot its familiar color. The yellow pigment is present but is masked by predominant green pigment from chlorophyll. But in the fall, partly because of changes in the period of daylight and changes in temperature, the leaves stop their food-making process. Chlorophyll breaks down and the green color disappears allowing yellowish colors become more visible.      At the same time other chemical changes may occur and cause the formation of additional pigments that vary from yellow to red to blue. Some of them give rise to the reddish and purplish fall colors of leaves of trees such as dogwoods and sumacs. Others give the sugar maple its brilliant orange or fiery red and yellow. The autumn foliage of some trees, such as birch and hickory, shows only yellow colors. Many oaks and others are mostly brownish, while beech turns golden bronze. These colors are due to the mixing of varying amounts of the chlorophyll and other pigments in the leaf during the fall season.      Fall weather conditions favoring formation of brilliant red autumn color are warm sunny days followed by cool, nights with temperatures below 45° F.  Sugar is made in the leaves during the daytime; however, cool nights prevent movement of sugar from the leaves. From the sugars trapped in the leaves the red pigment called anthocyanin is formed.      The degree of color may vary from tree to tree. For example, leaves directly exposed to the sun may turn red, while those on the shady side of the same tree or on other trees in the shade may be yellow. The foliage of some tree species just turns dull brown from death and decay and never shows bright colors.      Also, the colors on the same tree may vary from year to year, depending upon the combination of weather conditions. The most vivid colors appear after a warm dry summer and early autumn rains which prevent early leaf fall. Long periods of wet weather in late fall produces a rather drab coloration. Droughts favor anthocyanin formation principally due to the indirect effects of soil water deficiency upon the metabolism of the plants. Drought conditions also favor red pigment formation due to the reduction of nitrate absorption.      Some of the most startling color combinations are to be found in the leaves of red and sugar maples, sassafras, sumac, blackgum, sweetgum, Northern red oak, scarlet oak, sour-wood, and dogwood. Gingko, hickory, and yellow poplar produce few if any anthocyanins and usually just display a golden yellow. Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension Service in Rowan County. For archived garden columns or other information, visit the Rowan County Master Gardener web site at www.rowanmastergardener.com , e-mail Darrell_Blackwelder@ncsu.edu