Autumn is the time of year when the weather turns crisp, monarch butterflies and many birds head south, asters and goldenrods are in full bloom, and the leaves of deciduous trees convert from their summer greens to a kaleidoscope of yellows, reds, purples, and oranges. Many of us in the northern states marvel at the beautiful displays, but rarely give a second thought to the processes that make it happen.

Throughout the spring and summer months, trees rely on packets of a green substance called chlorophyll, which is present in most leaf cells. This amazing material utilizes energy from the sun to convert water and carbon dioxide into sugars and starches that provide the trees with food. With these carbohydrates, the trees add wood to their trunks, grow new branches and roots, store food for the next spring, and stay strong to fight off diseases and insects.

In addition to green chlorophyll, leaves also have xanthophyll and carotenes, which are orange and yellow in color. These colors are covered by the more dominant chlorophyll throughout the summer. As temperatures drop and daylight wanes in the fall, the carbohydrate production comes to a halt. The chlorophyll in the leaves breaks down and the green color fades, making room for the oranges and yellows that were hidden all summer. Reds and purples are created by other chemical processes that create anthocyanin. It is the variety of mixtures of these compounds that creates the array of colors we see.

You may have also noticed that the colors vary from year to year. The intensity and length of the color display depends on the temperature, sunlight, and precipitation while it is developing. Anthocyanin formation is best when there are low temperatures that hover above freezing, causing maples to be brilliant red, while an early frost will dull the reds.

As you’re enjoying the fall color show this year, remember all the chemistry that’s going on behind the scenes. You may even appreciate it more!