Remember, fall is for planting

This is a great time to select and plant your pansies, spring flowering bulbs and new trees and shrubs. “Fall is for Planting” was a major promotion of the American nursery industry for many years back in the days of my youth. They haven’t promoted that phrase for a couple of decades but it still applies. We have had such significant tree and shrub damage from the drought this summer that you may want to replace trees or shrubs you know are dead or add new trees and shrubs to your landscape. As long as you water them periodically this winter they will begin to grow roots and will start to adapt to their new environment. Fall planted trees and shrubs get a head start on spring plantings and are usually better prepared to handle their first hot summer.

Fall color is great garden art and leads to many questions. Temperature, soil moisture, sunlight and day length all influence the intensity and quality of the fall tree color. Night length is the biggest factor in this amazing process. Plants use the chlorophyll, which appears as green in the leaves to manufacture carbohydrates which are stored each growing season in the tree branches, buds and roots to support the next year’s growth. As the days get shorter and the nights longer the cells at the base of the leaf where it meets the stem or branch divide rapidly but do not expand. This makes an abscission layer of corky cells that begin to block carbohydrates going from the leaf to the branch and new minerals from the roots going to the leaf.

Fall color occurs at the same time each year since it is based on day length regardless of whether we are warm or cold. During the growing season chlorophyll is constantly being replaced as the sun breaks it down. As the flow of minerals from the roots is stopped, the leaves cannot make new chlorophyll and this process is slowed down and then stops. As the chlorophyll disappears we begin to see the other colors that have been in the leaves all the time but were covered up by the green chlorophyll including the yellow pigments of xanthophylls and the orange pigments which are carotenoids.

The red and purple pigments are anthocyanins and are manufactured each fall from the sugars that are trapped in the leaf as the process of abscission progresses. As the abscission cells become more dry and corky the leaf/stem connection cells are weakened and the leaves will drop from the tree. Some trees will hang onto their old leaves all winter but the other pigments like chlorophyll will fade out in the sunlight or when the leaf cells freeze and die. The only pigments left in the end will be the brown of the tannins.

Please spend some time outside to enjoy the beautiful and ever changing symphony of fall colors and consider doing your part of “Fall is for Planting” to add more trees and shrubs to your yard.

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