Demystifying the Causes of Brilliant Fall Colors

We all enjoy the colors of autumn leaves. The changing fall foliage never fails to surprise and delight us. Did you ever wonder how and why a fall leaf changes color? Why a maple leaf turns bright red? Where do the yellows and oranges come from? To answer those questions, we first have to understand what leaves are and what they do.

The chemicals

Four main groups of biochemicals are responsible for the various yellows, oranges, reds and browns that we see in the fall - chlorophyll, carotenoids, and anthocyanins Each has its own color and chemistry. Varying amounts of these chemicals will give subtle variations in color from one leaf to the next or even from tree-to-tree.

Chlorophyll

The green color that we see on most plant leaves throughout the spring and summer is due to the pigment called chlorophyll. Chlorophyll is one of several pigments that gather energy from sunlight in the process of photosynthesis.  As daylengths shorten and temperatures get cooler, chlorophyll is broken down faster than it's produced. What essentially happens, is that there is a lack of chlorophyll, and so the other chemicals in the leaves become more prominent.

Carotenoids

Many of the yellows and oranges we see in nature are the result of the various carotenoid compounds. The best-known carotenoids are the ones that give carrots their orange color. Carotenoids play a minor role in photosynthesis so they're present throughout the growing season, but are only revealed when chlorophyll breaks down. Brilliant colors are more often seen when the fall weather has warm, sunny days with cool nights between 32° and 45 °F. Indeed, shade-grown leaves often are a duller color than leaves that are in the full sun, even on the same plant.

Anthocyanins

The reds and purples found during the fall are due to the anthocyanin compounds. These are produced when sugars combine with compounds called anthocyanidins. Bright, sunny fall days produce the best colors. Very little photosynthesis will occur on cloudy days while rain can actually leach out the anthocyanins and carotenoids from the leaves. Various combinations of anthocyanins and carotenoids can result in yellow, orange and red leaves all on the same tree. ...

As summer ends and autumn comes, the days get shorter and shorter. This is how the trees "know" to begin getting ready for winter.

It is the combination of all these things that make the beautiful fall foliage colors we enjoy each year. 

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Go out there and breathe in the fall crisp air while basking in the spectacular Fall colors.

Cheers,

Laura