By Judy Kunz, Colorado Master Gardener

Why Some Leaves Don’t Drop in the Fall

Most deciduous trees lose their leaves in autumn. The word deciduous comes from the Latin word “decider,” which means to fall down. Signaled by shorter days and a subsequent drop in temperature, trees stop making chlorophyll, the chemical that gives leaves a green color and provides energy for the plant. As a result, an abscission layer forms between the leaf stem (petiole) and the branch. This cuts off water and nutrients to the leaves, and they react by drying out and eventually falling off the tree. The leaves are no longer of use to the tree as the tree enters dormancy for the winter.

However, some trees such as oak, beech, witch hazel and hornbeam don’t completely form an abscission layer in the fall. They hold on to most of their leaves until the leaves succumb to wind, and eventually drop, or remain in place until the following spring when new, emerging buds push them out. This phenomenon is referred to as marcescence, which is rooted in the Latin word “marcescere,” meaning “to fade.”