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Finally Fall Color

University of Minnesota Extension, Stearns County News
September 30, 2015

Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns, Benton & Morrison Counties

Finally Fall Color
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (9/30/15) — Compared to previous years, this year it seems the leaves changing to their beautiful fall color is a bit delayed.  What causes the leaves to change colors? When can we anticipate the color change? How long will the colors last? There are so many questions that can be asked about fall foliage, some we can answer, and others don’t have such a clear answer.

The change in leave’s color is triggered by the decrease in daylight hours. As the amount of daylight decreases in the late summer and early fall, leaves form an abscission layer at the base of the leaf. This layer slowly reduces the amount of water and mineral supply to the leaf, reducing the amount of chlorophyll that is manufactured. The vibrant color pigments that were always there for most trees become unmasked as the more dominant chlorophyll decreases.

The colors we see come from the cells called pigments. Chlorophyll is the green pigment, and is critical in leaves for photosynthesis, the process of converting sunlight and water into sugars.  The red and purple pigments some plants produce are called anthocyanins, while the group of pigments called carotenoids produce the yellow colors. Anthocyanins aren’t always present in the leaves throughout the entire summer; many trees do not start producing these pigments until fall through a result of a complex interaction. A combination of both anthocyanins and carotenoids results in the deep oranges, bronzes, and fire reds.

The brilliance of colors each fall will vary depending on the temperatures and the moisture as the main influences. Adequate moisture throughout this growing season should contribute to good color, but abnormally warm temperatures without cool nights in September might have thrown off what the tree needs to produce spectacular color. A succession of dry warm, sunny days with cool, crisp nights seem to contribute to the intense colors. Freezing temperatures or frost unfortunately kill the leaf cells and this will prevent the colors from developing. Another contributing factor is the health of the tree, pest-free, and water and nutrient supply result in better color. It appears that a warm, wet spring, followed by favorable summer weather and the combination of warm sunny days and cool nights in the fall produces the best autumn colors.

The autumn color season in parts of Minnesota can experience two waves of color blasts. The sumacs typically start the fall color off as early as late August, while the maples, birch, basswood, dogwoods, and many other shrubs will peak near the last week of September. The second wave of color comes from the oaks and aspen.  We also shouldn’t forget about the only deciduous conifer in Minnesota, the tamarack or larch.  This species will add a sea of golden yellow to many low land areas in middle to late October.

Although the autumn season indicates shorter days and longer nights, cooler temperatures, and the upcoming winter, it packs a punch of gorgeous interest to our landscape that makes it all worthwhile. For an update about current fall color throughout Minnesota, visit


Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
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