Why do Leaves Change Colour During Fall?

45697055_505506409967546_3299602680917262336_nIt is the wonderful season of Autumn, also known as Fall here in the northern hemisphere and the colours are coming in breathtakingly in Southern Ontario.

Have you taken a weekend to go out with friends and family to check out the fiery oranges, reds, and yellows our local trees have to offer? Like many people, I wondered why do leaves change colours in the fall?

I was always told that trees have cycles and they sense weather changes or that leaves are shed off to protect the tree from frigid winter temperatures. While these answers were partially right, they were not the full answer, and most of the puzzle was solved for me as I made my way through the upper years of school!

So Why DO Leaves Change Colour in the Fall?   

All biological organisms have an inner cycle known as the Circadian Rhythm which regulates all day to day processes. One of the main ones, being the sleep and wake cycle. The moment your body is exposed to sunlight, it tips of a chain of chemical reactions in the brain that tell the body to stay awake, and then go to sleep when the sunlight is no longer available.

A similar happens with trees. Near Earth’s poles, there is a large swing in daylight hours during the summer and winter. When trees sense that the days are getting shorter, it is a sure sign to them that they need to begin shedding those leaves.

day night

Now I’m sure we all have heard of chlorophyll? The chemical that makes leaves green? There’s nothing complicated there really. You see, chlorophyll is also the chemical in leaves involved in making energy for the tree. When the tree no longer needs the leaf to make energy, the chlorophyll being to break down and die off.

So, the leaf is no longer green.

What’s left behind are other chemicals that were being overshadowed by the green green chlorophyll!

We call these chemicals, carotenoids. They are essentially natures pigments that give us the colours we find in fruit, some flowers and even egg yolks!


Now there are many different carotenoids, and each has its own colour. The colour it does not absorb from the sun is the one that bounces off and reaches our own human eyes.

Did you know? The colour the pigment gives off depends on the size of the pigment itself? Pigments come in all sorts of sizes, usually in the form of long chains.

If you ever notice a tree changing from red to orange and more over days, the reason is that one pigment has degraded and left another behind.

Once the process is over, the leaf is weakened and the leaves begin to…..fall. Or an autumn storm may sweep through and shake the leaves off their branches.

I love that these pesky pigments are able to transform our cities into colourful and breath-taking landscapes each year! They have inspired a whole new colour palette for fall fashion and home décor. And make holidays like Halloween and Thanksgiving just so special! And of course, I just cannot stop taking those pictures!

If you are still looking at catching some time with the colours over the coming weeks, here is a link to some wonderful parks in Ontario, Canada.

Bring snacks, a warm coat, maybe an umbrella and of course a camera, and you’re all set!

fall lake