Gardening Tips and Highlights

Why leaves shed in fall

Wouldn’t it be nice to enjoy those brilliant autumn colors all year-rather than for a few short weeks? Maybe so, but the changing leaf color each fall is part of an important and complicated process that ends in their being shed at the end of each growing season. 

The actual term used to describe this process of leaf drop is known as “abscission”. Although some parts of trees like stems and buds can handle freezing temperatures, most leaves cannot. So, in order to protect themselves, trees and plants shed diseased, damaged or dead tissue (namely leaves), while simultaneously sealing the point where the leaf petiole connects to it.  

Known as the abscission layer, it consists of unique cells that can separate from each other based on certain physiological occurrences. As changing climate and light conditions of autumn evolve, hormones within trees change too. 

The most notable is “auxin”, which is produced in the leaves and body of trees and plants. This balance of auxin levels between leaves and branches is key to determining if and when leaf drop occurs. During the active growing season, production rates of auxin in leaves are consistent with other parts of the plant or tree.  

As long as these rates are steady, the cells of the abscission layer remain connected, which in turn, keeps leaves attached. However, as days shorten and temperatures cool, auxin production in leaves starts to decrease in response to changing conditions. As a result, fracture lines develop at the base of the leaf petioles and scarring builds up at the same point to form a protective barrier. Eventually, it’s just a matter of time before wind or rain provides that last nudge and the leaves are released, at least for most trees.  

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