If you haven’t been outside lately, you’re missing the fabulous fall foliage. As the days get shorter and the temperature drops, trees sense the approach of winter. During the fall, the green canopy of summer transforms into a colourful smorgasbord of reds, oranges, and yellows. Have you ever wondered what triggers the leaves to change colour?
During my horticultural studies, my ornamental plant professor explained it best. Leaves change colour because of a chemical shift in the foliage. During the summer, leaves produce chlorophyll, which is used to absorb sunlight, which is then turned into glucose – in other words, photosynthesis. As the tree prepares to hibernate chlorophyll production slows down and the glucose and nutrients from the leaves are absorbed by the branches, trunk, and roots. Since chlorophyll makes the leaves green, the remaining pigments in the leaves take over. Yellow and orange leaves contain carotene (the same pigments that give carrots their bright orange colour). Red and purple leaves contain anthrocyanins (which give radishes and red roses their vibrant red colour).
Pretty technical, I know, but it does shed some light on the chemical shift that the leaves are experiencing. Of course, there are other factors that influence how vibrant the colours become including temperature and soil moisture. In southern Ontario, our fall colours seem to pop after we enjoy several consecutive warm, sunny days and cool nights. I can’t imagine living somewhere in the world where they don’t experience changing seasons. As we transition into each new season, the garden is filled with new splendors to explore!