The Colors of Fall
BY: Colby Griffin
NC Cooperative Extension
Horticulture Extension Agent
Reds and oranges and yellows, Oh my! Have you ever wondered what causes many of our deciduous trees and shrubs to give us the array of colors we enjoy viewing this time of year? It is a slow chemical process within the leaves that’s triggered by cooler temperatures and the gradual decrease in day length.
However, the shorter day length contributes the most to the emergence of colors. Leaves serve as factories throughout the spring and summer to make the carbohydrates and sugars necessary for plant growth. This takes places in leaf cells containing the pigment chlorophyll, which give leaves their green color. Carotenoids are also produced throughout the year and these are pigments that we see as yellows, oranges, and browns. These are also the pigments that we see reflected in the vegetables of carrots and squash. Anthocyanin pigments produce the reds, blues, and purple colors. Blueberries, beets, and certain apples produce these pigments in abundance. You’ll notice these red pigments in dogwoods and maples. These pigments are produced mostly in the fall in response to the increased amount of sugar within the leaf from the growing season. For most of the year these colors are masked by the greater amount of chlorophyll within the leaf. As autumn progresses the chlorophyll breaks down and the yellows and reds begin to shine through. Warm, sunny days followed by cool, crisp autumn nights are ideal for adequate color display. The most vivid of colors tend to appear after a warm and dry summer with early autumn rains which prevent early leaf fall. Long periods of wet weather in late fall can produce a dull coloration.
As the season progresses further there are continued changes happening at the base of the leaf as well. A special layer of cells begins to form where the leaf attaches to the tree. As this layer of cells grows and thickens it weakens the bond between the leaf and tree, thus enabling the leaf to eventually separate and fall. During this process, the tree also heals itself after the leaf has fallen and forms a visible leaf scar. Once leaves have fallen they become valuable in the form of mulch and organic matter as they decompose. Leaves are an abundant source of nutrients, specifically calcium and potassium which were once part of the soil. As you enjoy the colors of fall consider this quote by French author Albert Camus, “Autumn is a second spring where leaf is a flower.”
Colby Griffin is the horticulture agent for NC Cooperative Extension in Franklin County. If you have any questions about this article or other gardening issues, he can be reached at firstname.lastname@example.org or 919-496-3344.