Why Do Leaves Change Colors in Autumn

You may be familiar with the process of photosynthesis in which plants make their own food using chlorophyll and the energy from sunlight. But did you also know that chlorophyll plays a big role in the changing colors of leaves in the fall? This unit on the science of leaf colors is for kids 9 to 12 years old and will help answer the question: Why do leaves change colors in the fall?

The science behind leaves changing colors

In the spring, many plants burst to life growing the green leaves they need in order to survive. Plants, including their leaves, are made up of hundreds or thousands of tiny cells. And inside these cells are organelles called chloroplasts that contain chlorophyll.

Chlorophyll is a pigment that is responsible for absorbing light for photosynthesis. It also gives plants their green color because it reflects green wavelengths in white light.

In the fall, however, the leaves on many trees and other plants turn a different color before falling off the branch as winter approaches. Here’s why…

The end of photosynthesis

Did you know that chlorophyll isn’t the only pigment found inside plant cells? Carotenoids and xanthophylls are orange and yellow pigments that are also present. But the chlorophyll is so strong in the spring and summer that you cannot see the other two.

Shorter photoperiods, however, cause plants to start preparing for winter. The photoperiod is the amount of time each day that a plant (or other living creature) receives sunlight. In the spring and summer, the photoperiod is getting longer; the sun is out for more hours of the day. And this tells plants to grow.

The summer solstice is the longest day of the year. In the northern hemisphere, it usually falls sometime around June 21st. In the southern hemisphere, it happens within a day or so of December 21st.

The days start to get shorter after the summer solstice. Chlorophyll starts to break down as the daylight starts to get shorter in the autumn. And these other pigments now emerge turning leaves yellow or orange. Some leaves start to produce anthocyanins when the chlorophyll breaks down. Anthocyanin is another pigment and turns leaves red or purple.

But other factors can affect how quickly a tree drops its leaves. Early freezes and storms can cause trees to lose their leaves before they have a chance to change color. The best years for seeing beautiful autumn leaves are those in which the summer ends hot and dry, followed by sunny fall days with cool nights.

Activities related to autumn leaves

Here are some of our printable resources for helping your child learn more about the changing colors of leaves.

English Language Arts

For centuries, autumn has been the subject of poems, music, and art. The beautiful colors created by nature and the symbolism of death and renewal have provided writers and artists with inspiration…and continue to do so!

Activity: Download our Autumn Poem page and have your child write their own autumn-themed poem. You can also visit this page on Poets.org ahead of time to read some fall poems (some with lesson plans!) written by literary greats such as Emily Dickenson, Robert Frost, and others. We also have plenty of fall poems that might provide some inspiration!

Science

Activity #1: This lesson talks about four different types of pigments found in plants: chlorophyll, carotenoid, xanthophyll, and anthocyanin. Print our Leaf Pigments activity sheet and fill in the missing information. Simply give some facts about each pigment and color in the leaf to correctly reflect that pigment.

Activity #2: Leaves aren’t the only part of the plant that produces pigments. Rummage through your refrigerator and pantry and find examples of vegetables, fruits, and other colorful plant parts that display the pigments. Print our Plant Pigment worksheet and write them in the correct column.

You might also like our fall cryptogram word puzzles.