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.
This article appears in Oct 16-22, 2008.
