As the autumn leaves fall from the trees, it’s time to consider the wonders of nature because trees are smarter than you think. It’s miraculous that trees recognize the days getting shorter, the temperatures getting cooler and begin the same preparation that we do for the upcoming winter.

Although the changing colours of leaves are a spectacular event to watch, the question of why leaves change colours in autumn is inevitably asked. What is it about trees that cause their lush green leaves to change into bright yellow, orange and red and then fall to the earth? Better yet, why does the intensity of colours differ from year to year?

While many people might think that the cool weather or frost is the main reason leaves change their colour, they are only partly correct. Although the temperature does determine the colour and intensity of the leaves, it is only one environmental factor for fall’s glorious colours.


Photosynthesis is a process used by plants to convert sun energy into chemical energy and released at a later time to fuel the plant’s activities. The term photosynthesis means “pulling together with light”.In the case of trees, its leaves are nature’s food factory because the tree draws water from the ground through its roots and pulls carbon dioxide from the air. It turns water and carbon dioxide into oxygen and glucose along with chemical called chlorophyll to make photosynthesis happen. Chlorophyll is the biological substance that gives plants their basic green color.

In the fall, the trees disassemble the chlorophyll and reabsorb any useful nutrients like nitrogen and potassium into the twigs that close the pathways to the leaves. At the leaf’s stem a special layer of cells develops that gradually severs the tissues that support the leaf, seals the cut and leaves behind a leaf scar.

The now useless leaves fall off and the tree prepares for winter dormancy. Because there is not enough sunlight during the winter months or sufficient water for the trees to take up, they live off the nutrients that they stored during summer.

The Transition:

Trees have many accessory pigments in their leaves beside the green that’s produced by chlorophyll. One of the other colour pigmentations is beta carotene (carotenoids), which produce the same substance that’s found in making carrots and squash orange. Another element is xanthophyll, which makes things yellow.

When the tree stops producing chlorophyll, the tree starts to create a substance called anthocyanins. Anthocyanins give colours to things like cranberries and red apples and are water soluble. They appear in the watery liquid of the leaf cells. While both chlorophyll and carotenoids are constantly present during the spring and summer growing season, most anthocyanins are produced only in autumn.

As the green fades from the leaves, the other pigments have the chance to show their true colours and these bright and vibrant colours remain. The intensity of the colours is dependent upon the amount of anthocyanins production in the tree’s system. Some trees produce this ingredient faster than other trees. For trees that have an abundance of anthocyanins, they skip right over the first stages of yellow or orange and go directly to the red leaf state.

Season to Season:

Have you ever wondered why some years the fall leaves seem to have a spectacular showcase of radiant colour while other years the leaves are sort of dull and drab? Well, it’s all about the weather.

The pigment of the fall leaves are susceptible to temperature, light and water supply. Each of these parts plays an important role in influencing the degree and duration of fall colour. The cooler temperatures will favour anthocyanin formation producing bright reds, but a bright, sunny fall will cause the pigments to break down too quickly. If an early frost arrives, the frost will weaken the brilliant red colours and your leaves will end up brown because of the cold. Rainy and/or overcast days tend to increase the intensity of fall colors. The best time to see the beauty of autumn’s colour is on clear, bright crisp days.

Mother Nature:

Since the season is so short, it’s worthwhile to take advantage of it while you can and get out and enjoy the beautiful fall foliage with friends and family. Plan a hike or take a drive in the countryside to enjoy what fall has to offer and witness Mother Nature at her best.  A few of our favourite spots to hike and see the changing leaves are the Bruce Trail, Webster’s Falls in Dundas, as well as Spring Valley in Ancaster.