Why Do Leaves Change Color In The Fall?
Get ready for nature’s big reveal! As the days shorten and nights cool, the trees are about to explode into a kaleidoscope of reds, yellows, and oranges. Every autumn is unique—like unwrapping a colorful present, you never know exactly what you’ll get! Watch to discover why leaves change color, and soak in the magic before they drop and the season fades away!
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VD: Barbara, a white woman wearing a black long-sleeve shirt with black sheer sleeves with dots, is standing in front of a grey background.
00:05: Background shows yellow and orange leaves falling with the wind.
00:33: An image of a green leaf that absorbs most of the visible light spectrum, reflecting only green light.
01:00: A green circle is superimposed on an image of the molecular structure of a chlorophyll.
01:18: An image of a green leaf that absorbs most of the visible light spectrum, reflecting only green light to human eye.
02:01: A green circle fading out.
02:13: Orange, red, purple, and yellow circles fading in.
02:18: Orange and yellow circles are superimposed on an image of the molecular structure of a carotenoid.
02:35: A green circle superimposes the orange and yellow circles and fades out to reveal these circles.
02:59: Red and purple circles are superimposed on an image of the molecular structure of an anthocyanin.
05:09: An image of a blue water droplet containing brown soil with a plant growing out of it.
05:15: An image of a thermometer.
06:23: A background showing trees with green, red, orange, and yellow leaves.
Transcript: As the weather starts to cool in the fall, the leaves on trees go through a magical transformation, turning brilliant shades of red, orange, yellow, and even purple. But what’s really happening behind this colorful change?
The answer lies in pigments, which are natural chemicals or molecules that absorb and reflect light in different ways, giving leaves their colors. During the spring and summer, leaves are hard at work making food for the tree. They use sunlight to create energy through a process called photosynthesis. The green color of leaves comes from a pigment, chlorophyll – a chemical that helps capture sunlight and turn it into food. We see green leaves because chlorophyll absorbs both the blue and the red wavelengths from sunlight and reflects the green wavelengths.
But as the days get shorter and the temperatures drop, trees start preparing for winter by slowing down food production. Chlorophyll begins to break down, and as it fades away, the green color disappears.
With the green gone, other pigments in the leaves can finally shine through. Carotenoids are pigments that give leaves their yellow and orange colors, and they’ve been in the leaves all along, but hidden by the chlorophyll, revealing the yellows and oranges only when the green pigment disappears. You see carotenoids in carrots, daffodils, and bananas. In some trees, especially maples, another pigment called anthocyanin forms, producing reds and purples. The vibrancy of reds and purples depends on how much sugar is trapped in the leaves and how cold the nights get. You can see anthocyanin in cranberries, red apples, and blueberries.
In addition to the pigment in the leaves breaking down, trees are preparing to drop their leaves and go through a hardening process to survive the cold winter. This process involves the tree hardening the connection between the leaf and the twig and concentrating the sugar. A special layer of cells will form between the leaf and twig, blocking nutrients and trapping the leaf with the sugars that control the vibrancy of reds and purples from anthocyanin. Once the connection hardens, the twig cells dehydrate and shrink, transforming into a hard, glass-like structure to prevent freezing.
But every year the colors vary! Some years, the colors are vibrant. Other years, the colors are dull. Why? The amount of moisture in the soil and year-round temperatures also affects autumn colors. A late spring, or a severe summer drought, can delay the onset of fall color by a few weeks. A warm period during fall will also lower the intensity of autumn colors. In short, a warm wet spring, favorable summer weather, and warm sunny fall days with cool nights normally produce the most brilliant autumn leaf colors.
As you can see, the tree will stop sending water and nutrients to its leaves altogether, and the leaves will fall to the ground. But for a few weeks in autumn, we get to enjoy nature’s beautiful display of colors—a reminder of how trees prepare for winter by conserving energy and protecting themselves from the cold months ahead.
