September 26, 2001
Stillwater Gazette
Betsy Halden

With the recent events in our country, many Americans are more than ever appreciative of comfort and stability. I have always found comfort in things of beauty, including the Minnesota outdoors. In a few short weeks the fall leaf color will be at its peak in our area. Each year Minnesotans and many visitors enjoy the dazzling color display in the St. Croix Valley. Scenes of stately maples turning shades of orange and red, and of red oaks ablaze with crimson leaves accented by a bright blue autumn sky appear like calendar pictures. These are scenes that may come to thought when we think of fall colors. Have you ever wondered how the leaves of trees and shrubs are able to create such a colorful display? Why is fall color better in some years than in others? There is no simple formula to predict color for a given area of the state. Intensity, type and duration of color, and date of peak color are determined by complex environmental factors and the genetic makeup of the plants themselves.

A summer leaf is green because of the presence of a group of pigments known as chlorophylls. Chlorophyll pigments help the plant manufacture food. They are plentiful in leaf cells during the growing season, and their green color masks the colors of other pigments present in the leaf. As autumn approaches, shortening day length causes the supply of chlorophylls to dwindle, and their ability to mask other pigments is diminished. Then other pigments like the carotenoids, which actually have been present in the leaf all summer, begin to show through.

Carotenoids are responsible for the colorations of yellow, brown, orange, and many intermediate hues, give characteristic color to carrots, corn, daffodils and bananas. They also give color to the fall leaves of deciduous trees like ash, aspen, birch, ginkgo, hickory and honey locust.

Reds and purples, and their blended combinations that color the autumn leaves of red maple, white ash and red oak come from another group of pigments called anthocyanins. Unlike the carotenoids, anthocyanins are not present in the leaf during the growing season. Instead, the anthocyanins develop in late summer in the say of leaf cells. Not all trees are capable of producing anthocyanin pigments, and even those that are, depend on the breakdown of sugars in the leaf in the presence of bright light. In fact, when the days of autumn are bright and cool, and the nights are chilly but not freezing, the most brilliant colorations usually develop. Wet, cloudy warm weather or exceptionally low temperatures in early fall tend to mute the anticipated fall leaf color display. Finally, trees growing in dense shade usually do not develop the vibrant colors that trees of the same species produce in full sun.

Visit “Explore Minnesota” www.exploreminnesota.com for additional tourist information. Click on the underlined text “Rainbow Routes: 10 Fall Color Drives” for specific scenic routes.

I also encourage you to visit Carpenter Nature Center. Enjoy the hiking trails, the beautiful vistas and the fall colors. Sunday, September 30 is their Fall Festival.

Special Note and Congratulations: The Washington County Fairgrounds Master Gardener demonstration garden recently received a “Search for Excellence” award at the Master Gardener State Conference in St. Paul. Our thanks to all who visited the garden during the Washington County Fair and throughout the season. Congratulations to Kent Mitchell, garden coordinator, and to the Washington County Master Gardeners who worked to provide and maintain the garden’s beauty.

Other Washington County Master Gardener garden projects are the Wilder Forest Butterfly Garden, the landscaping project at the Historic Courthouse in Stillwater, and The Carpenter Nature Center garden.

Betsy Halden is a Master Gardener with the University of Minnesota Extension Service. University of Minnesota Extension Service materials were consulted in the preparation of this column. You can reach Betsy Halden at eahalden@comcast.net