What causes leaves to change color in the fall?

I am a Florida native living in Kentucky.  

Upon hearing that, people typically apologize.  Then they respond with something like,  “Why on earth would anyone move from Florida to Kentucky?”   Actually, I couldn’t be happier about the transition. After 41 years in Florida, I love living somewhere with four seasons.

Trees in my backyard changing color in the fall

When my oldest son was in kindergarten 14 years ago, I remember one of his lessons asked him to draw a tree and show how it changes during the different seasons of the year.  I’m quite sure they were looking for something like this:

A drawing showing how a tree changes appearance with the changing seasons

My son looked at me, clearly puzzled by the directions.  After all, in Florida, the trees don’t change throughout the year.  To him, it sounded like a ridiculous assignment. I had to pull up some online pictures and explain to him that in other parts of the country, trees look different depending on the season.  He truly didn’t know.

During our first year in Kentucky, I couldn’t wait for the leaves to change.  I became absolutely giddy at the first hint of color in the trees. I annoyed my friends and family to no end by my excited squealing every time we passed a tree in its full autumn glory.  

Autumn leaves changing color and falling to the ground

Before we moved north, I thought that it was the cooler weather that signaled the leaves to change color in the fall. However, once here I discovered that some leaves start changing well before the temperatures start to drop.  Clearly, I realized, it isn’t temperature which triggered the leaves to change. So what was the reason?

If, like me, you are curious about what causes leaves to change color in the fall, you might enjoy checking out my mini course on The Science of Autumn Leaves.  In it, I review plant physiology, the function of leaves, and the biological reasons behind the fall leaf color change.

It's easy to perform paper chromatography to separate the different pigments in leaves.

Included are several optional experiments that can be done at home.  In one of the experiments, your students can use paper chromatography to separate the different colored pigments from leaves.  While conducting this hands-on activity, they will discover that the beautiful colors we associate with fall leaves are actually hidden in the leaves all year long, but are merely hidden by the bright green pigment produced during the spring and summer.

It's easy to perform paper chromatography to separate the different pigments in leaves.

 Don’t be fooled by the name; this mini course (and the experiments within) can be done all year long, no matter the season!  In fact, I have experience performing these experiments in the dead of winter.  Check out the module to see how.


Click Here for the Free Module

Why do leaves change color in the fall?  Is it the cooler temperatures?  Less rainfall?  The shorter days?  What is the biological reason for leaves to change color?  Learn more in the free online mini course (with fun hands-on experiments!)

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Hi, I'm Kristin!

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