Ever wonder why leaves change color? Did you know that fall’s vivid colors are actually hidden underneath summer’s green color? Also, the main reason for color change is not weather, but light, or actually the lack of it. Learn more.
Why do Leaves Change Color?
First of all, not all leaves turn vivid colors in the fall. Only a few of our many species of deciduous trees—notably maple, aspen, oak, and gum—produce stellar performances for our annual autumn spectacular in North America.
Several factors contribute to fall color (temperature, precipitation, soil moisture), but the main agent is light, or actually the lack of it. The amount of daylight relates to the timing of the autumnal equinox.
As the autumn days grow shorter, the reduced light triggers chemical changes in deciduous plants causing a corky wall to form between the twig and the leaf stalk. This corky wall eventually causes the leaf to drop off in the breeze. As the corky cells multiply, they seal off the vessels that supply the leaf with nutrients and water and also block the exit vessels, trapping simple sugars in the leaves. The combination of reduced light, lack of nutrients, and no water add up to the death of the pigment chlorophyll, the “green” in leaves.
Once the green is gone, two other pigments show their bright faces. These pigments, carotene (yellow) and anthocyanin (red), exist in the leaf all summer but are masked by the chlorophyll which helps plants absorb sunlight. (The browns in autumn leaves are the result of tannin, a chemical that exists in many leaves, especially oaks.)
Sugar trapped in autumn leaves by the corky wall (the abscission layer) is largely responsible for the vivid color. Some additional anthocyanins are also manufactured by sunlight acting on the trapped sugar. This is why the foliage is so sparkling after several bright fall days and more pastel during rainy spells.
What Brings the Best Fall Foliage?
In general, a wet growing season followed by an autumn with lots of sunny days, dry weather, and cold, frostless nights will produce the most vibrant palette of fall colors. This vividness is especially true of red leaves, such as those on sugar maples and red maple trees.
Check your long range forecast to see whether a dry autumn is in your future.
Of course, if freezing temperatures and a hard frost hit, it can kill the process within the leaf and lead to poor fall color. Check the frost dates in your area!
Also, drought conditions during late summer and early fall can trigger an early “shutdown” of trees as they prepare for winter, causing leaves to fall early from trees without reaching their full color potential.
Where Can You Find the Most Beautiful Autumn Leaves?
Does your area experience fall foliage? Some level of autumn foliage changes in most regions of North America, but it’s New England, the upper Midwest, the Rocky Mountains, and parts of the Appalachians that hold the jackpot for leaf peepers. The right climate and light conditions and an abundance of the tree varieties that hoard colorful pigments come together in these places.
While tradition has it that Columbus Day weekend is when the color peaks in New England, the mythical maximum occurs in northern Maine in mid- to late September and “travels” south, reaching the Connecticut shore by late October.
Learn More about Leaves
Check out our Fall Foliage Map to see when leaves start to change in your area. Don’t forget to make a foliage report to let others know when the trees in your neighborhood reach their peak, too!
Below is an animation of the changing leaves from past years, based on the foliage reports from our readers. This map can give you an idea of when leaves typically start to change across the country.
How are the fall leaves looking in your area? Let us know below! We hope you have a beautiful autumn.