As sure as the days are getting shorter, the leaves on the trees are changing colors.
Green leaves give way to a bright painter's palette of red, purple, yellow, orange and brown. It is this time of year when everyone wonders why leaves change colors.
Specific colors are caused by specific plant pigments. The normal green color of foliage is from chlorophyll, the chemical substance that captures energy from the sun and converts it to sugar. Fall colors are caused by other pigments. The reds and purples are caused by anthocyanins, yellows are due to the presence of xanthophylls, oranges are caused by a combination of carotenes and xanthophylls and browns are the result of tannins present in the leaf. Most of these substances are present throughout the growing season, but are masked by the green chlorophyll.
As summer days get shorter, chlorophyll begins to break down and these pigments emerge. However, changing colors is not simple -- weather conditions play an important part in the process. Warm, bright, sunny fall days and cool nights are ideal for good color. The sunny days encourage photosynthesis and sugar accumulation in the leaves. The more sugar in the leaves the brighter and more impressive the fall display. Cloudy days and warm nights prevent sugar accumulation so colors are less vibrant.
This year's display is not as spectacular as in past years. Heavy rains in the early spring followed by hot, dry weather during the summer have made it difficult for trees to produce the energy they need for a stunning display.
-- The Garden Calendar is sponsored by K-State Research and Extension-Douglas County and written this week by horticulture agent Bruce Chladney. For more information, call 843-7058, between 8 a.m. and 5 p.m. Monday through Friday.