Fall color displayed in flowers, leaves

Fall is a great time to visit the colorful hardy mum gardens on the oval at the University of Oklahoma in Norman or to plant and enjoy hardy mums in your own yard. As your summer annuals start to wither with the cooler temperatures it is time to add spunky pansies to your sunny flowerbeds to enjoy all winter. It is time to plant flowering kale and cabbage, trees, shrubs and to sow tall fescue grass seed.

One of the best shows on earth is the changing fall colors on our deciduous trees and shrubs every autumn. Our trees have been cloaked in different tones of green leaves all summer. These leaves are literally millions of cells using natural sunlight to convert water and carbon dioxide into sugars in an amazing process called photosynthesis.

Every leaf contains three natural substances which are the pigments that determine leaf color. Chlorophyll   provides the green color, carotenoids provide yellow, orange and brown tones and anthocyanins provide the red tones. Chlorophyll and carotenoids are in all leaf cells, all the time, during the growing season but the chlorophyll covers up or overpowers the carotenoids so that we see green leaves during the growing season. Most anthocyanins are produced only in the fall and then only in certain conditions and not in all trees.

Chlorophyll is the most important as it enables the plant to use sunlight to produce food. Carotenoids produce the bright yellows and oranges we see in many fruits and vegetables like corn, carrots and bananas. Anthocyanins add the red we see in apples, cherries, strawberries and cranberries.

As the days get shorter, the sunlight is less intense and the temperatures cool, trees and other plants produce less and less chlorophyll. They reach a point when chlorophyll production stops and then the green of chlorophyll disappears to unmask the yellows and oranges of the carotenoids that have been in the leaves all the time. In effect, fall color is the absence of chlorophyll that had provided the green pigment throughout the growing season.

Temperature, moisture and cloud cover all have a big effect on how much red color we get from year to year even on the species of trees most likely to redden up. Warm sunny autumn days with cool but not freezing nights, day after day, produce the best years for red colors. In the daytime the leaves still produce sugars as the chlorophyll decreases but cool nights keep the sap from flowing back to the trunk and roots. When these sugars are trapped in the leaves, anthocyanins are produced to recover valuable nitrogen, sulphur and phosphorus from the leaves before they abscess or drop. Saving these last nutrients helps prepare the tree for winter and will give it more energy next spring. This anthocyanin rescue effort, in the right conditions, adds the exciting red, purple and crimson tones to our trees’ fall colors.

Plant more trees to enjoy these fall colors in your yard.


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