Warm, Sunny Days and Cool Nights Produce Fall Foliage

By Jolyn Johnston-Myers
November 11, 2016

It’s not all the colors of a rainbow, but trees that turn red, purple, yellow, orange and brown in the fall do produce a wide color variation for us to enjoy.

K-State Research and Extension horticulturist Ward Upham says several forces are at work when trees turn color in the fall.

“That’s right. So, at this time of year what we’re getting into are shorter days and cooler weather,” Upham said. “And that’s what triggers these trees to start to turn color.”

Specific plant pigments determine individual colors. Foliage gets its normal green color from chlorophyll, the substance that captures the energy of the sun. However, chlorophyll naturally breaks down over time.

“This time of the year, it’s still breaking down, but it’s not being replaced quick enough,” Upham explained. “And so that green color fades…so then the other colors are going to be revealed.”

Upham says most of the pigments that produce fall colors are present throughout the growing season, they’re just masked by chlorophyll.

“Like the yellows, that is just a carotenoid or xanthophyll that is already there – same thing with the oranges,” Upham said. “Now in the case of the reds and purples, that’s anthocyanins, and those are actually made as the chlorophyll breaks down.

“But for most of our colors, it’s just actually seeing something that has been masked in the past,” he added.

Browns are the result of tannins present in the leaf. The best conditions for producing good color is warm, sunny days and cool nights. The sunny days encourage photosynthesis, which causes sugar to accumulate in the leaves. A higher sugar content results in more intense leaf color.

The weather also impacts how long a tree maintains its fall color. Reds, yellows and oranges are short-lived when trees undergo frosts and freezes.

With the unusually warm fall we started having this year, it was almost like the trees were confused into thinking summer wasn’t quite finished.

Or maybe that was just me.