Ever wonder why the leaves turn red?

One of the most enjoyable things about autumn is the spectacular display of many deciduous trees and shrubs as their leaves change from green to a kaleidoscope of yellows, oranges, reds and purples. Many plants are bought for this feature alone as it provides a beautiful marker between the oppressive summer heat and the coming winter chill. It is no wonder that many people choose autumn as their favourite season. But why do certain plants produce these stunning autumn colours and why are some years more impressive than others? 

Like most of us, plants do what they can to escape the chilling effects of winter. Some produce thick waxy leaves that insulate against the cold and some trees lose their leaves to escape the cold. It is this second group of plants that provides us with spectacular autumn colour. So let’s take a trip with a leaf as it travels from the green of summer to the fiery tones of autumn. 

A leaf is basically a factory that converts energy from the sun to carbohydrate energy that it uses to grow and stay healthy. One of the most important members of this factory is the green pigment called chlorophyll. Its job is to trap the energy from the sun so it can be converted to sugar. In spring and summer, the leaves are packed with it, so we see them as green. As the days get shorter and the temperature starts to drop in autumn, deciduous trees and shrubs get the message that it is time to close the factory and shut down for winter. Instead of just dropping green leaves many plants pack-up as many nutrients as possible and ship them off to the branches and roots to be used the following spring. The green chlorophyll and other nutrient-rich molecules are dismantled and sent out of the leaf. As the chlorophyll level drops, other leaf pigments start to show through, yellow and orange carotenoids, red anthocyanins and brown tannins. Different plants contain different mixes of these pigments which is why we see such a rainbow of colours. Environmental factors such as temperature, light intensity and rainfall affect the intensity of the colour we see. Sunny, cool, dry autumns give the most colourful displays. 

So next time you are taking in the wonderful autumn display of trees such as the vibrant red Acer October Glory® or the brilliant yellow Ginkgo biloba, think of how busy the plant is getting ready for winter and enjoy with an added sense of awe and wonder.