Why do leaves fall in autumn?

In autumn the trees put on a show. Green leaves turn yellow, orange and red, then drift down to the ground for you to crunch through. But why do trees let their leaves go?

Less sunlight in autumn

In summer the days are long and bright. Leaves use sunlight to make food for the tree, a bit like a kitchen full of busy cooks. But in autumn the days get shorter and the sun is weaker. With less light, the leaves can’t make much food anymore.

The green fades away

The green colour in leaves comes from something called chlorophyll. It is the part that catches sunlight to cook food. When the tree stops making food, the green chlorophyll fades away — and other colours that were hiding all along finally show. That is the yellow and red we love in autumn!

Time for the tree to rest

Soon the tree lets its leaves drop. Why? Through cold winter there is little water and light, so the tree takes a long rest, like a deep sleep. Dropping its leaves helps it save water until spring, when warm sunny days return and brand-new green leaves grow.

Wonder fact: Trees that keep their leaves all year, like pine trees, have thin needle-shaped leaves that don’t dry out — so they stay green even in winter!