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Autumn’s Sublime Display of Color

Sometimes Mother Nature puts on quite a show, and I think Autumn color is some of her best work. The science behind the color is a fascinating study.

The display of color we enjoy each fall is explained by understanding plant pigments, the physiology and anatomy of leaves, and the influence of climate and seasonal weather conditions, according to a timeless Purdue Extension publication, FNR-FAQ-5, "Why Leaves Change Color – The Physiological Basis," authored by William R. Chaney, professor emeritus (former professor of tree physiology) at Purdue University. Much of what follows is excerpted from that resource.

Four leaf pigments account for leaf color and its changes in the autumn: chlorophyll (green), carotenoids (yellow to orange), anthocyanins (red to purple), and tannins (brown).

Chlorophyll, essential for photosynthesis, is responsible for the green color in leaves and other plant parts. Chlorophyll is continuously being produced and destroyed throughout the growing season within tiny organelles called chloroplasts in plant cells. In the fall, nitrogen and phosphorus are slowly withdrawn from leaves for storage in twigs and branches during the dormant winter period. Gradually, production of chlorophyll fades, leading to other colors being seen.

Carotenoid pigments are responsible for yellow and orange pigments. These pigments are also in the chloroplasts and assist chlorophyll in the capture of sunlight for photosynthesis. Although these pigments are always present in the leaves, they are not visible for most of the year because larger amounts of green chlorophyll make leaves appear green. As production of chlorophyll declines, these yellowish colors become “unmasked” and give leaves part of their autumn splendor. Nutrient deficiencies, diseases or other stressors throughout the year can produce the same visual effect on leaves by reducing the normal production of chlorophyll. Maples, buckeyes, tuliptrees, sycamore, birches, ashes and many other trees display yellow coloration in the fall.

Anthocyanins are responsible for pinks, reds, and purples in leaves, and their color is influenced by cell pH. As days shorten, complex biochemical processes involving plant hormones trigger the formation of an abscission layer at the base of leaves and trap sugars produced by photosynthesis (still happening, but at a reduced rate). These sugars are available for anthocyanin production. Anthocyanins are usually not present in leaves until produced from sugars during autumn coloration. Trees that may turn red or purplish in the fall include flowering dogwood, red maple, sassafras, sumac, white oak, and others.

A few trees, such as some cultivars of Japanese maple, purple-leaf plum, and purple-leaf European beech have reddish leaves throughout the growing season due to anthocyanins in them. Chlorophyll is still there doing its work in photosynthesis, but the higher quantities of anthocyanins in these “purple-leaved” varieties mask the green chlorophyll. Not all trees have the genes required for the production of anthocyanin pigments, and therefore only turn yellow and brown.

Tannins, the waste products of cell processes, cause the brown hues in leaves, which persist following leaf drop. In some trees (beech is an example), the presence of tannins combined with carotenoids produce a golden yellow color. Tannins are bitter substances that color and flavor tea and cause unripe persimmons to pucker our mouth. These pigments are always present in leaves, but only become visible when chlorophyll and carotenoids disappear.

Hardwood trees generally display the most spectacular autumn color, but larches and baldcypress are two conifers grown in Indiana that drop all their needles each fall, and they offer autumn color in the process.

Trees of the same species may vary in color due to differences in amounts of soluble sugars available for anthocyanin production, and due to the effects of available sunlight and shading on leaves. A single tree may even have branches with different colored leaves due to one leaf shading another.

When can we expect the best fall color? That answer will vary each year depending on the weather, but fall colors typically begin in early October and may peak near mid-October in northern Indiana, and a little later in southern Indiana. A warmer fall so far this year may push peak fall color later than usual.

What about the best weather for fall colors? Fall weather will affect anthocyanins the most. Warm sunny days followed by cool, but not freezing, nights produce the brightest red autumn colors. Rain does not wash color away, but overcast conditions do reduce light intensity and rains and winds can sweep leaves off trees early. Freezing temperatures kill or severely injure the leaves, preventing physiological processes before pigments reach their maximum development.

Access the above-mentioned publication at Also find Purdue Extension Forester Lenny Farlee’s short video in which he explains fall color at


Above image by John Woodmansee

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