Why Do Leaves Change Color in the Fall?

A few years ago when we were playing outside in the fall leaves, Ruby asked me, “Why do the leaves change color?” So I started telling her about how the earth tilts in the fall making us get less sunlight which affects the amount of sun that the plant gets from photosynthesis and so on, but truth be told, her attention had wandered to something else before I could even finish my explanation. So we gathered a variety of multi-colored leaves, and I made a large mural on our wall to teach her more about photosynthesis and its role in the leaves changing color, but still, the answer was too complex.

Teaching Photosynthesis Wall Art

I continued learning more and more about photosynthesis all the while thinking of the Einstein quote,

“If you can’t explain it simply, you don’t understand it well enough.”

After watching countless videos (like this amazing one), reading numerous articles (like this very scientific one), and making a large photosynthesis mural in our new house, it finally dawned on me when I was invited to teach an art lesson in my daughter Ruby’s 1st grade class.

Photosynthesis Mural

For the art lesson, I chose to have the students make trees out of multi-colored leaves. I also wanted to do a mini-lesson about, you guessed it, why leaves change color! As I was thinking about where to start, this other Einstein quote was on my mind,

“Everything should be made as simple as possible, but not simpler”

It finally dawned on me that I needed to start with chlorophyll.

Chlorophyll

Chlorophyll is what makes leaves green, it is basically the heart of photosynthesis, and the absence of it in the fall is what makes the leaves change color. Eureka! This was it!

The hexagon shapes are the plant cell walls. The little circles inside are chloroplasts. Cholorophyll is what makes chloroplasts green.

So I began my mini-lesson by showing the students one green leaf. I explained how chlorophyll is what makes leaves green. They all said the word chlorophyll, and I showed them my chlorophyll poster. (Click here to see a really cool video of chloroplasts moving to music.)

Then, I explained how chlorophyll was a part of photosynthesis. Now, I know that photosynthesis is a complex system that even I struggle to fully understand, but I believe that children learn things in layers. By really understanding chlorophyll and then being introduced to photosynthesis, they are creating new pathways in their brains that will continue to be strengthened over time through repeated exposure.

Why Leaves Change Color

I had all of the kids take a deep breath in and I asked them what they just breathed in. “Oxygen,” explained one student. I then had them exhale and asked them what they just breathed out. Ruby was the only one who could tell me carbon dioxide. (She had an unfair advantage!)

I then explained how we breathe out carbon dioxide which is just perfect for trees because even though they don’t breath, they need to take in carbon dioxide to make their own food. As I explained the rest of photosynthesis and how trees take in carbon dioxide, water, and light (which is absorbed by the chlorophyll) which they use to make glucose (also known as sugar or sap) and then give off oxygen as a waste product (which is perfect for us!), I knew that I was going over their heads. I even told them, “I know that photosynthesis seems like a really big idea for a first grader to learn about, and I know that it seems like a confusing big new word, but the more you hear about it, the more you will understand it. All I want you to really remember right now though, is chlorophyll.”

Then I talked about how in the fall when the days are shorter and there’s not as much water, the trees don’t make as much chlorophyll and photosynthesis slows down until it completely stops. Chlorophyll is what makes the leaves green and as it goes away, we start to see some of the colors like orange and yellow that were in the leaf all along. The leaves that turn red and purple are from sugars that get left behind.

As the tree gets ready to hibernate for the winter, the veins in the leaves that carry the sap into the tree start to close by forming a separation layer. When the leaves finally detach and fall to the ground, they start to decay and turn brown.

Then I showed the children how to make their tree art. As I passed out the green leaves, I had them look at the green color made from chlorophyll, feel the veins that carry the sap from the leaves into the tree, and look at the stem where the separation layer is formed. As I passed out the orange and yellow leaves, I explained how these colors were already in the leaves and once the chlorophyll left, we could finally see them. When I passed out the red leaves, I explained how some leaves leave sugar behind, and it turns the leaves red. (Warm sunny days and cool, crisp, but not freezing nights make the most sugar get trapped in the leaf as its vein closes and makes the most brilliant of red leaves.) Finally, we put some brown leaves on the ground, and I explained that they are brown because they are decaying.

Leaf Art

The students that finished early were able to do some leaf rubbings with crayons. This is an excellent way to really see all of the veins in the leaves.

Leaf Crayon Rubbings

At the end of the lesson, I brought all of the children together again and asked them, “So why do leaves change color in the fall?” Hands shot up all over the place and kids told me how it was because of chlorophyll. We all said chlorophyll again together, and I told them to remember that chlorophyll is what makes leaves green, that chlorophyll helps the leaves absorb light during photosynthesis, and that in the fall without as much light and without chlorophyll, the leaves change color.

In a Nutshell

Chlorophyll is a green pigment that allows plants to absorb light during photosynthesis. It is what makes leaves green. In the fall, when there isn’t as much sunshine and water, the leaves don’t produce as much chlorophyll, and so they lose their green color. The yellow (from xanthophylls pigments) and orange colors (from carotenoid pigments) were there all the time in small amounts, we just didn’t see them because they were covered up by the green chlorophyll. The red and purple colors we see are made from sugars that were left behind in the leaf (called anthocyanins). When leaves fall from the trees and start to decay, they turn brown (tannins are the last pigments to decay and they are brown). (Source)

In Conclusion

So now, when the next one of my children asks, “Why do the leaves change color?” I will simply explain that it’s because of the chlorophyll. When I have their attention and curiosity, I will explain more and more layer upon layer, lesson upon lesson, day by day until their curiosities are fully satiated and we are ready to move on to the next question!

Further Resources

• Fall Leaf Art Projects – by me!
• Autumn Leaves and Fall Foliage: Why Do Fall Leaves Change Color? by Science Made Simple (This article gives two explanations, one with a really simple explanation and one with a more complex explanation.)
• The Science of Color in Autumn Leaves by the United States National Arboretum (A very comprehensive explanation that I used as a resource for this article.)
• Why Leaves Change Color by the USDA Forest Service (Another very comprehensive article that I used as a resource.)
• Why Do Leaves Change Color in the Fall? YouTube video by Super Scienced (A 2:43 minute video that provides a simple and accurate explanation with cartoon animation that also explains the difference between coniferous and deciduous trees.)
• Why Do Trees Shed Their Leaves In Autumn Season? YouTube video by T-Series Tree Hut (This is an excellent 2:43 minute video. All of the videos in this series do an amazing job of answering typical questions posed by children in a way that includes the scientific information presented in a simple and easy to understand way with entertaining cartoon graphics. The speaker has an accent and there are some translation mistakes, but it’s still the best thing out there and my kids love them!)