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Why Leaves Change Colour and Other Fun Fall Facts

by Gary Reading, Oct 2018

As fall arrives you may find yourself feeling a little depressed about the shorter days and crisper temperatures. But when the leaves begin to turn, transforming from a quiet green into a vivid palette of reds, oranges, yellows and golds, it could make anyone—even a cottager—wonder what all the fuss around summer is about.

Here are some amazing facts you probably didn’t know about this spectacular autumn show, which will make this year’s all the more awe-inspiring.

I like to think of fall from an Alice In Wonderland perspective; that is, autumn is a time when we shrink in proportion to our gardens while the leaves ‘bloom’ above us.  And each year, nature unveils new surprises, dazzling us with colors and combinations so vivid and daring as to leave little doubt as to her ability to create designs far superior to our own.

While it’s generally believed that cold weather causes a tree’s leaves to change color, the process is in reality a bit more complex. Weather can affect the intensity and duration of color, but the color itself is a part of each tree’s biology. And just like flowers in a garden, every tree has its own colors and ‘bloom’ period that occur at different times during the fall season.

Why do leaves change color?

Leaves change color due to the process of photosynthesis. During the growing season, leaves act as food factories for the plant, capturing sunlight to turn carbon dioxide and water into oxygen and sugar. A chemical called chlorophyll, which absorbs light energy, is responsible for making this happen. It is also the reason why most leaves are green.

In fall, as temperatures cool and days grow shorter, leaves stop their food-making process. As the chlorophyll naturally breaks down, the green color disappears from the leaf surface. Yellow and orange, two colors which until now have been masked by the green, start to become visible.

Some trees like maples, sourwoods and sweet gums, however, start making brand new pigments of their own as their chlorophyll breaks down. These trees produce brilliant shades of red, scarlet and purple. Often you’ll see these colors mixed in with the leaves’ underlying orange and yellow pigments, making for a dazzling show.

As the season progresses and the temperatures drop further, the cells near the juncture of the leaf and stem weaken and the leaf starts to fall from the tree. The additional pigments begin to break down, the leaf dries up, and only a brown color remains. Some plants, like oaks, retain their brown foliage for a good part of the winter.

Weather has a big effect on color

Weather conditions can effect leaves’ color and duration and are the reason why each year the landscape looks slightly different. These conditions include temperature, amount of sunlight and available water supply.

Lots of sunlight combined with low temperatures, for instance, produces brighter reds but shortens their duration. An early frost, however, spells the end of the show. And drought stress during the summer can result in early dropping of leaves before they have a chance to develop any color at all.

Surprisingly, a combination of rain and overcast days tend to increase color intensity.

The best and brightest show, however, usually follows a growing season with lots of rain followed by a dry spell.