Why do Leaves Change Color?

In the autumn when the weather cools, something amazing happens up in the trees. All the green leaves begin to change colors – yellow, red, orange, and brown – but what makes the leaves change color, and what makes them fall? To answer these questions, we need to learn a little bit about how leaves work. Leaves are the food factory of the plant. Trees take in water through their roots, and sunlight and carbon dioxide through their leaves. They use the energy from the sunlight to turn water and carbon dioxide into oxygen and glucose – a kind of sugar. The oxygen is released back into the atmosphere where it can be used by animals. The glucose is used to feed the plant. The process plants use to make their food is called ‘photosynthesis,’ and it is possible because plants have a bright green chemical inside of them called ‘chlorophyll’ which allows them to absorb the energy from sunlight.

Chlorophyll is what makes leaves look so green! As summer ends and fall begins, the days begin to grow shorter and the nights longer, meaning that less light is available. This is a signal to the tree that the growing season is at an end and that winter is coming. During the winter, there is not enough light or water for the broad-leaved trees to make their food. Instead, they will rest and live off of the food they stored during the summer, so they begin to shut down their food factories. The trees stop sending water to the leaves. All the chlorophyll in the leaves gets used up, and the tree doesn’t make any more. With the chlorophyll gone, the green color fades, and other colors become visible in the leaves. Different types of trees may have different chemicals in their leaves, which is why leaves from different trees may turn different colors in the autumn. Once the leaves have dried up, they begin to drop off, and soon the branches of the tree are bare. Trees that lose their leaves every winter are called deciduous trees. Not all trees lose their leaves, however: evergreen trees keep their leaves all year long. Evergreen leaves, usually called needles, are small and tough. They won’t be damaged by the cold winter weather, and they won’t cause the tree to lose water like bigger leaves do. Because of this, evergreen trees don’t drop their needles in the fall and so can stay green all year round. This helps evergreens to survive in climates that are too cold for deciduous trees. Now that you know why the leaves change color and fall in the autumn, take a look and see if you can find out what kind of trees live near you!