The Science Behind Fall Colour Change in Leaves

What makes you think of autumn? Is it biting into crisp, sweet apples? Cool breezes coming out of the north? Pumpkins everywhere?

For many residents of the northern United States and Canada, one of the signals that summer is shifting into autumn is the fall foliage. The bright green leaves that told us that spring had finally taken hold begin to shift into a riot of yellow, orange, and red that draws visitors from all over, eager to see the glamorous colours of the trees before the leaves fall, leaving us with just pine needles and evergreens until spring comes around again.

But what brings on that riot of colour?

Chemical Composition of a Leaf

Every plant leaf has at least two pigments in its cells which give it color. The first is chlorophyll, the chemical we all learned about in grade school that plants use to process sunlight into energy. Chlorophyll is also the pigment that gives leaves their green color.

The second pigment is called carotenoids. These yellowy pigments are present in vegetables like corn and carrots, and are responsible for the yellow to orange hues in those plants.

Plant leaves always have chlorophyll and carotenoids throughout the warm weather, but the deep green of chlorophyll covers up the yellow pigments of carotenoids. As the weather cools and days shorten, trees produce less chlorophyll in their leaves, which allows the carotenoids to show through, giving hillsides and lanes their iconic yellow to orange rainbow.

What about red leaves? 

Red leaves are caused by another pigment, called anthocyanins, who are also present in strawberries, cranberries, red apples–you get the idea. Not all trees contain anthocyanins; in some leaves, if the tree’s sap has become acidic, the anthocyanins will react in such a way that the leaves turn red. Red leaves are very influenced by the weather, the environmental conditions, and may vary from year to year.

Fall Foliage in Ontario

Ontario is one of the best places in Canada to tour the fall foliage. Colors usually begin to shift in mid-September, and continue to change through October in many resort locations. If you want to plan your visit for peak foliage, check out resources like 400ElevenTravel Ontario, and Ontario Parks Fall Colour Report to decide when you should travel. As for the “where”, one of the 300+ provincial parks managed by Ontario Parks would be a great bet and Algonquin is the most popular among them. Consider referring to one of these two articles that might help you plan your next Fall trip in Ontario Parks

Best Ontario Parks to visit in the Fall

Best day trails in Algonquin to enjoy Fall colours

Whether you want to drive, hike, or boat during this time of the year, the weather is lovely and the scenery is amazing. Check out the fiery reds, brilliant oranges, and exquisite yellows that make the Ontario fall foliage such a gorgeous sight to see.


Guest post by Sakthi.

Sakthi is an outdoor enthusiast from Toronto and he runs his own camping blog in Ontario that explores Ontario Parks and camping.