It’s now officially chilly around here, so my curiosity turned towards the leaves. Specifically, how and why they change to such lovely colours. Turns out, they don’t really change to yellow and orange so much as let their true colours come through. (That’s your cue, Cyndi!)
The green in leaves is due to the presence of chlorophyll. That’s the chief ingredient for the process of photosynthesis, turning sunlight, water and carbon dioxide into glucose… yummy tree food. (also good on pancakes) If you ever mow a lawn in white shoes, you know that chlorophyll is a strong green pigment, and that’s what you’re seeing when you look at a green leaf.
As the days get shorter, the trees take the hint to begin hibernating for the winter. In shutting down photosynthesis food production, the green chlorophyll drains out of the leaves and the true colour of the leaf, be it yellow, brown, orange, or some mix of the above, can now be seen. (the colour is caused by carotenoids, much like those newfangled orange carrots)
Red leaves, however, are not a natural colour but the result of specific circumstances. If the autumn days tend to be sunny, but then the nights are particularly cold (but not freezing) then we will see more vibrant red leaves. The red is caused by anthocyanins, which only enters the leaves as an elite rescue force. In such weather conditions the glucose (food) gets stuck in the leaf, unable to completely drain into the tree, and the red anthocyanins are created to recover nutrients from the leaves before they fall off.