Sunflowers

Although popular culture has embraced the myth that sunflowers always follow the sun, this is inaccurate. Only young flowers “move” to face it throughout the day. Once they reach maturity, they stop sun-tracking—their blooms forever turned eastward.

Recent studies suggest that sunflowers share a common mechanism with human beings, circadian rhythms organized around a 24-hour day. Scientists hypothesize these circadian rhythms—behavioral changes associated with an internal clock—explain sun tracking in young blossoms.

Young blooms face east at dawn to meet the rising sun. Then, throughout the day, they slowly modulate west as the sun moves across the sky. Once it sets in the west, the plants spend the night slowly turning eastward to start the cycle again.

As sunflowers mature, this process comes to a halt. Overall growth slows, and the flower’s circadian clock reacts most intensely to the sun’s early morning rays than those later in the day. As a result, the blooms gradually stop tracking westward altogether.