Why do leaves change colour in autumn?

IMG_0227Have you ever wondered why the leaves on deciduous trees change colour in the autumn?

Most of us will have a vague memory from science class at school that chlorophyll is the name for the green pigment found in leaves that acts like thousands of miniature solar panels capturing the energy from sunlight and converting it into energy that can be stored in the form of carbohydrates or sugar. This energy is used by plants for growth and is also the main source of carbohydrates that passes up the food chain feeding the world and also providing fuel and building materials.

IMG_1200Chlorophyll reacts to certain wavelengths of light but these are limited, to make the most of the light spectrum plants also use other pigments similar to carotene that can react with a wider range of the spectrum. These colours are hidden by the intensity of the green chlorophyll in plants with green leaves. However, once the days start to shorten and the temperatures drop this triggers a process called abscission, in simple terms ‘leaf fall’. Plants need to be thrifty though, the main elements that make up chlorophyll are iron and magnesium but these can be in short supply within the soil when the trees come into leaf in the spring so the trees carefully extract these elements, drawing them back into the tree to store away ready for the first flush of growth in the spring.  This is when the other pigments are revealed giving us the fantastic display of autumn colours.

Next spring at Le Jardin Creatif we will look at harnessing these colours to use as natural fabric dyes so follow our pots to find out more and sign up for one of our workshops. If you want to find out more about how plants work we will also be offering short courses in botany. Follow our blog at https://lejardincreatif.net or follow us on Facebook to keep up to date.


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