Why Leaves Change Color

If you live in certain parts of the world (especially the middle and eastern parts of the United States) you will see something happen each fall (autumn) that is almost magical. What is it? It is the changing colors of the leaves on many different types of trees. Some of the prettiest fall trees are:

  • Maple trees
  • Walnut trees
  • Sassafras trees
  • Sweet gum trees
  • Aspen trees
  • Oak trees
  • Gingko trees
  • Redbud trees
  • Dogwood trees
  • Pear trees

These trees (and every other tree that loses its leaves) are called deciduous trees.

A deciduous tree is a tree that loses its leaves every fall and grows new leaves each spring. Each year deciduous trees go through a process in which their green leaves become bright yellow, gold, orange and red for a few weeks before turning brown and falling to the ground.

The purpose of a leaf

During the months of September, October, and November, the changing colors of a tree’s leaves is something we all enjoy. But believe it or not, the trees don’t change their colors just so we will have something pretty to look at. There is actually a reason for the many colors of fall.

Photosynthesis is the process trees (and plants) use to make their food. Taking energy from the sun, water from the ground, and carbon dioxide from the air, they make glucose (sugar) to ‘eat’ so they can grow into strong, healthy trees.

The leaves of a tree (or plant) are where photosynthesis happens because the chlorophyll in the leaves is what makes photosynthesis possible. Chlorophyll also has another job…it is what makes leaves green.

So…as long as the leaves are able to soak up enough heat and energy from the sun to make food, the leaves on the tree stay green. But when the seasons begin to change and the weather turns colder…

Why leaves change colors…or do they

Leaves change color because they are hungry…sort of.

When the seasons change in places where deciduous trees grow, the days get shorter (there is less sunshine) and the weather gets colder. When this happens it is harder for the chlorophyll in the leaves to make the food needed to stay green. So instead of making more food, the leaves start using food they have stored away for this time of year.

As the leaves use the food (glucose) that has been stored away, a layer of cells forms at the bottom of each leaf. These cells are spongy like a cork. Their job is to act like a door between the leaf and the rest of the tree—a door that closes very slowly and doesn’t ‘shut’ until all the leaf’s food is gone.

While this is happening the colors in the leaves of the trees are able to show through. That’s right…the red, yellow, gold and orange colors are hiding in the leaves all summer long. The colors just can’t be seen in the summer because of all the chlorophyll in the leaves. REMEMBER: Chlorophyll makes plants and leaves green.

Once all the food is used up, the leaves turn brown, die and fall to the ground.

What about the rest of the tree

You might be wondering how the rest of the tree keeps growing when the weather turns cold and the leaves die and fall off. Doesn’t the rest of the tree need food made by the tree’s leaves?

No, not really. The tree trunk and branches get food from the roots of the tree. The roots supply water, vitamins and minerals they get from the ground. Yes, trees need sunshine and warm weather to grow, but they also need time to rest—like bears who hibernate (sleep) during the winter.

So…the next time you see a nice green leaf on a tree, you will know why it won’t stay that way for long.

 

Read more about Plant Facts for Kids