Photoperiodism

The response of an organism (in this case plants) to seasonal changes in day length. Flowering and other developmental processes are regulated in response to the photoperiod (day length).

For example, the most important factor initiating leaf color change is photoperiodism. As the photoperiod (day length) decreases, some of the water and nutrients are drawn into the stems away from the leaves and eventually back to the plant for its benefit in preparation for winter.