Fall Tree Color: What, How, Why, and When?

During the fall, the local (and nationwide)tree canopy becomes a beautiful array of colors. The greens of spring and summer leaves are now turning into yellows, oranges, and reds of autumn. This change occurs because of cooling temperatures, as trees prepare for winter dormancy by resorbing and storing precious nutrients. The most vivid displays are produced when the weather has been warm, but not hot, and soil moist. Unseasonably high temperatures and drought will cause dull colors and early leaf drop.

Changes in leaf color are the result of biochemical processes where shorter days, lower temperatures, moisture levels, and the overall health of trees interact. The pigments expressed in this interplay of changing fall color are chlorophyll (green), carotenoids (yellow), and anthocyanins (red and purple). Orange foliage is created by a combination of carotenoids and anthocyanin.

These photosynthetic pigments utilize different wavelengths of sunlight, and convert water and carbon dioxide into glucose (sugar) and oxygen through photosynthesis.

Trees produce and use sugars and other nutrients for growth in spring and summer and store these energy reserves for use during the winter, when they are dormant and need them to survive. Changing leaf color indicate that trees are preparing for winter dormancy, conserving energy, and storing nutrients in their limbs; leaves gradually die, forming an abscission zone at the stem and then drop off. The leaves of some trees, such as oaks, beeches, witch hazels and hornbeams, turn brown but remain attached to the tree until spring, a phenomenon called marcescence.

Chlorophyll is the primary photosynthetic pigment that helps trees convert sunlight and carbon dioxide into sugar (glucose), and makes leaves appear green. As temperatures decrease and the days become shorter, nitrogen-rich chlorophyll is broken down and resorbed into storage proteins in the bark which causes the green in leaves to fade. . From the fading green, yellow emerges as carotenoid pigments are no longer masked by chlorphyll. Shades of reds and purples will also appear; developing during the late summer months in leaf cells. Anthocyanin is produced slowly, so some tree leaves show a mixture of green, yellow, red, and orange dependent on how temperatures and moisture change during various fall seasons.

Fall color varies by location and type of tree. In Maryland, native maples are particularly showy, red maples turn red - scarlet; and sugar maples yellow – orange. Native oaks turn red, brown, and russet; hickories golden bronze; dogwoods and sweet gums display reddish purple color. While it’s difficult to predict peak fall foliage colors, College Park typically hits its peak in lake October. Unfortunately, this year’s intensity may be diminished due to the past hot and dry weather we experienced this autumn.

Provided by the City's Tree and Landscape Board