We have begun one of the greatest natural shows on earth and it happens every fall. It is never the same from year to year but it happens very near the same time every year when the days get shorter and the nights get longer and cooler. The big show is the symphony of fall color we get to enjoy as our deciduous trees and shrubs prepare to shed or drop their leaves for winter. I’ve often wondered if autumn was named fall because of the falling leaves? Some trees have already started changing colors after our early flirtation with the 32 degree freeze mark a couple of weeks ago. Many other trees are still a vibrant green and even producing new growth but all deciduous trees have started or will soon start the process of sugar storage, shutting down their seasonal food production and shedding their leaves before they freeze as part of the annual ritual of winter survival.
There are 3 main pigments that star in this annual fall color show. They are chlorophyll, which provides the green color we see in leaves most of the year and is the workhorse of photosynthesis that uses sunlight to make sugars which are the food that fuels our plants. Carotenoids produce the yellow, orange and some tones of brown. They are at work in the leaf cells but are “masked” or covered up by the green chlorophyll most of the growing season. Occasionally the carotenoids show through in bananas, daffodils, corn, carrots and others. Anthocyanins produce the reds, oranges and blue or purple colors in red apples, grapes, cherries, strawberries, blueberries and cranberries besides the bright fall leaf colors that take our breath away. The anthocyanins are water soluble and we get the best fall colors when we have warm days and cool but not freezing nights when the leaf is still making sugars in the fall but not removing them all from the leaf. These excess plant sugars give us the bright colors of fall as the chlorophyll production shuts down. Chlorophyll production slows down and then stops at slightly different times in different tree or shrub species based on day length and temperatures. As the green chlorophyll stops production and gets used up or destroyed we can now see the yellow carotenoids that have been in the leaf all the time and the red, orange and purple tinted anthocyanins created by the autumn production of excess sugars. Some trees, like poplars, only show the yellow. Other trees show the yellow carotenoids and then the red or orange anthocyanin. Others like Bradford Pears and many maples seem to go right from green to tinges of red or purple.
Day length and cool weather are the most important triggers for fall color and are pretty much the same year after year but we get big variations in the other factors of light intensity, soil moisture and temperature that affect our deciduous trees and shrubs differently from year to year and assures that the fall color extravaganza is a new and different show each year. Fall is also a great time to plant new trees and shrubs to create shade for future summers and dazzling fall colors in future years
Rodd's Seeds of Wisdom 