Leaves change color in the fall because there’s less daylight.
The reason can mainly be chalked up to the shorter days. According to the United States National Arboretum, the green pigment in leaves, called chlorophyll, is what is responsible for photosynthesis, essentially the process of converting sunlight and water into food for the tree. So as the day shortens, there is less sunlight, and hence less “food.” As a result, the chlorophyll in the leaves dies off along with its green pigment. And xanthophylls, the yellow-colored pigments, and carotenoids, which are orange-colored pigments, are now suddenly visible without the presence of the overpowering chlorophyll. The red or purple pigments, however, are produced in the autumn by anthocyanins. That’s why you’ll sometimes see tinges of red on an otherwise yellow leaf. As autumn continues, these pigments break down just as chlorophyll did—all except for the brown-colored tannins.
The weather affects color intensity.
Some years produce spectacular reds and purples, while other years are heavy with yellows and browns and pale in comparison. When a few warm, sunny autumn days and cool but frostless nights come one after the other, it's going to be a good year for the brightest reds and purples, says The Department of Forestry and Natural Resources. Plenty of rain throughout the growing season also plays a part in producing a bolder palette. If there has been a drought during the growing season, however, the leaves may fall from the trees before they even get a chance to turn colors. And if there was an early frost, leaves won’t change to red or purple at all. A lack of wind and heavy rain throughout the autumn helps to prolong the display.
The species of the tree can predict what color its leaves will change.
Particular trees tend to produce a distinct palette, says the U.S. Forest Service. A few of the more common ones are:
- Oaks: red, brown, or russet
- Hickories: golden bronze
- Aspen and yellow-poplar: golden yellow
- Dogwood: purplish red
- Beech: light tan
- Sourwood and black tupelo: crimson
- Red maple: brilliant scarlet
- Sugar maple: orange-red
- Black maple: glowing yellow
- Striped maple: almost colorless
The prime time for leaf peeping is never the same.
In the Northeast and Midwest, leaves are just beginning to turn in early September; the foliage season ends completely in the Southeast in November. Though, to encounter a locale’s most vibrant display, you’ve got to find the sweet spot, generally only about three weeks long. The majority of peak times hit sometime in October, but they can vary by a week even within the same state, and certain weather conditions can make them come even earlier than usual. So if you’re planning a peeping excursion, be sure to look up your region’s peak time now on the 2015 Farmers’ Almanac website so you don’t miss it. You can also check The Foliage Network for weekly updates and webcams covering the constantly changing foliage in the Midwest U.S., Northeast U.S., and Southeast U.S. If New England is your destination of choice, discover the best scenic foliage drives, courtesy of Yankee Magazine.