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Fall Color

University of Minnesota Extension, Stearns County News
September 24, 2014        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns & Benton Counties


Fall Color
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (09/24/14) — The leaves have started to change colors already, and the peak will soon be upon us.  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 is called anthocyanins, while the group of pigments called carotenoids produces 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 fiery reds.

The brilliance of colors each fall will vary depending on the temperatures and the moisture as the main influences. A succession of dry warm, sunny days with cool, crisp nights seem to contribute to the intense colors. More anthocyanin production (reds and purples) occurs with increased sugars in the leaves; the sunny, warm days with cool nights trigger an increase in sugar content in the leaves. 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 plants, 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 the 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.  So get outdoors and take in the colorful palette nature paints us this time of year.

For an update about current fall color throughout Minnesota, visit   


Photo credit: Karl Foord, Autumn Blaze Maple (Acer x freemanii 'Jeffersred')


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