Fall is a beautiful time of year in Illinois. Leaves change color from green to red, yellow, purple, brown and orange. Do you know why leaves change color?
In the fall, with each passing day the amount of sunlight is less. The sun is not as high in the sky as it is in summer, either. There is a chemical in leaves that makes food for the tree. The chemical is called chlorophyll. It gives leaves their green appearance. As the amount of daylight gets shorter in fall, chlorophyll starts to disappear. Other chemicals in the leaves now show up. All leaves have some yellow pigment in them, and many have red tones as well. But these colors cannot be seen in the spring and summer because there is so much chlorophyll.
In some tree leaves, food is produced on bright, sunny fall days. The food may not be moved out of the leaves to the other parts of the plant as fast as it is in summer. The more food trapped in the leaves, the more colorful they are. Bright red and purple colors are the result. The sugar maple (Acer saccharum), for example, is one of the most colorful fall trees. Its leaves are full of sugars that have been produced by the chlorophyll but that haven't been moved to the rest of the tree. The sugars react to the sunlight and to the cooler weather by turning bright colors.
Weather helps to determine how colorful leaves will be. Plenty of rainfall in the summer helps trees to have healthy leaves. Healthy leaves have beautiful fall colors. Bright, sunny skies in late summer and early fall help to make red, yellow and orange leaf shades. Having many cloudy days in late summer and early fall may lead to more gold and yellow fall colors.
Leaf color can also be affected by the type of soil the tree is growing in. If there is not much rain in the fall, the leaves may drop from the trees without changing color. If temperatures get too cold, leaves may die without changing color.
Trees in Illinois that have red, orange and red-brown leaves in fall include red oak (Quercus rubra), sugar maple, flowering dogwood (Cornus florida), persimmon (Diospyros virginiana) and sweetgum (Liquidambar styraciflua).
Trees with leaves that turn bright orange and yellow include sugar maple, cottonwood (Populus
deltoides), black cherry (Prunus serotina), ash (Fraxinus spp.), buckeye (Aesculus spp.), birch (Betula spp.), hickory (Carya spp.), sassafras (Sassafras albidum) and yellow poplar (Liriodendron tulipifera).
Get outside this fall and enjoy the beautiful Illinois landscape!