Not all leaves turn vivid colors in autumn. And not all places get to experience fall foliage. But most parts of North America have some level of autumn foliage change.
Most of the attention goes to the most northern states, especially New England, as places to see spectacular colors in a wide area. I can see a great road or hillside and even just a few backyard trees on fire with autumn here in Paradelle.
If you are one of those “leaf peepers” who seeks out the foliage, you might know the answer to the why of autumn color. It is a combination of the right climate and light conditions and an abundance of the right tree varieties.
Typically, Columbus Day weekend is the color peak in New England. Up in Maine, it can start in mid- to late September and then it starts to move south. It varies year to year based on conditions but peaks in Connecticut in late October and is still strong in New Jersey at the end of October.
So, you start with the deciduous trees (those that lose their leaves) that have the best color, which are the maples, aspens, oaks, and gum trees.
Next, you need to start losing daylight. The amount of daylight we get is tied into the autumnal equinox and, as days grow shorter, the reduced light triggers chemical changes in the trees (and other deciduous plants).
A cork-like “wall” called the abscission layer forms between the twig and the leaf stalk. Eventually, this blockage will cause the leaf to fall because it blocks off the vessels that both supply nutrients and water and allows anything to exit. The simple sugars in the leaves are trapped. Without, light, nutrients and water, there is no production of the green pigment, chlorophyll, in leaves.
But, two other pigments will take over and react with the sugars: carotene (yellow) and anthocyanin (red). They are actually in the leaves all summer but they are masked by the chlorophyll. Tannin, a chemical that exists in many leaves (especially oaks), is what creates the browning of the leaves.
You will get the most brilliant color after a few bright fall days. Cloudy and rainy days produce more pastel shades, so, a dry fall produces the biggest explosion of really vibrant colors.