How do trees know when to shed leaves?

From the National Arboretum: As the days get cooler and frost is in the air, deciduous trees and shrubs put on an autumn show in all shades of red, yellow, purple, and brown. read more

Shedding leaves and growing new ones depends not only on temperature but also on how long the days are. Beeches, for example, don’t start growing until it is light for at least thirteen hours a day. That in itself is astounding, because to do this, trees must have some kind of ability to see. It makes sense to look for this ability in the leaves. read more

Many trees and shrubs lose their leaves when they are still very colorful. Some plants retain a great deal of their foliage through much of the winter, but the leaves do not retain their color for long. read more

The connections between cells become weakened, and the leaves break off with time. Many trees and shrubs lose their leaves when they are still very colorful. Some plants retain a great deal of their foliage through much of the winter, but the leaves do not retain their color for long. read more