Fall leaf colors, pumpkins and cool temperatures are all signs of fall. As the temperatures become cooler, leaf color changes will become more dynamic. So, why do leaves turn from green to vibrant red, orange, yellow or purple?
Leaf color comes from pigments. There are three pigments that color leaves: Chlorophyll are green pigments. Carotenoids are yellow, orange and brown pigments. Anthocyanins are red and purple pigments.
During the spring and summer, chlorophyll is produced inside leaves. Carotenoids are also present during the growing season but are not visible during the tree's growing season because they are masked by chlorophyll.
As days grow shorter (amount of sunlight decreases) and temperatures become cooler, the production of chlorophyll decreases and eventually stops. As the amount of chlorophyll decreases, the carotenoid pigments become visible.
In the fall, some trees also produce a group of pigments called anthocyanins. These pigments will mask the yellow pigments.
The amount of yellow in the fall was determined during the growing season and will not be affected much by changes in weather. Red pigments are in the process of forming in the fall and will be affected by the weather. Bright sunlight, cool temperatures and excess plant sugars within leaf cells are needed for the production of anthocyanins. So, the more warm, sunny days in the fall, and the cooler the nights (but not freezing), generally the more brilliant the red and purple fall colors.
Tan and brown fall colors are caused by tannins, which accumulate as the chlorophyll disappears.
The timing of color change varies by species. As well certain colors are characteristic of particular species.
Fall temperatures, wind and precipitation will have an effect on how long the leaves are on display. A severe frost will kill the leaves, turning them brown and causing early drop.
"The Miracle of Fall", http: //www.urbanext.uiuc.edu/fallcolor, is a University of Illinois Extension Web site that has links to live foliage cameras showing fall color at various stages. The site also includes information on dates and locations of fall festivals and events, plus suggestions for the best places in the Illinois, Indiana, Michigan and Wisconsin to visit to find fall color.
If you are planning to take a walk in the woods to observe fall color, another Extension Web site, "A Walk in the Woods," http://www.urbanext.uiuc.edu/woods, is designed to provide an interactive way to enjoy a visit to the woods. This site is designed for children, but adults will also enjoy the information.
If you plan to take an all-day trip, visit "Illinois Mile after Magnificent Mile" Web site http: //www.enjoyillinois.com. The site provides weekly updates of fall color in Illinois.
Now, get out and enjoy nature's autumn farewell.
Master Gardener training to be offered
If you want to learn more about gardening and share your knowledge with others, the University of Illinois Extension Master Gardener volunteer program may be for you.
Master Gardeners are adults interested in learning more about lawns, trees, shrubs, flowers, vegetables, the environment and much more. Master Gardener trainees receive 60 hours of in-depth unbiased, research-based horticulture training from University of Illinois Extension educators and specialists. A Master Gardener Intern is expected to return 60 hours of volunteer service in the year following their graduation. Classes will be offered on Thursdays from 9am to 4pm, starting January 22 and ending April 2, 2008.
Applications are available through Nov. 7. If you would like an application or more information about the Sangamon-Menard unit program, phone 782-4617.