Following the Sun

October 16, 2020

Sunflower Field

Sunflowers facing east

Photographer: Kathy Arbuckle
Summary Author: Kathy Arbuckle

Late July and August is sunflower time in eastern Washington State. Many farm fields are filled with the cheerful faces of huge, yellow blooms facing east to greet the Sun each morning. Young sunflowers have the ability to track and follow the Sun as it passes east to west, displaying heliotropism, the diurnal movement of plants in response to the direction of the Sun.

Researchers discovered that this is accomplished during the day by the plant growing slightly more stem on its east-facing side to cause the flower head to gradually face west, while at night it grows a longer stem on the west-facing side to return the bud to facing east. This cycle is repeated every 24 hours, according to the plant's internal circadian clock.

Sunflowers stop this mechanism at maturity and from then on set the blooming flowers facing east permanently, benefiting the plant's ability to attract bees and other pollinators to their golden, sun-warmed flowers. Photos taken on July 20, 2020.

Photo Details: Top - Camera NIKON COOLPIX P90; Software Nikon Transfer 1.3 W; Exposure Time 0.0040s (1/250); Aperture ƒ/5.6; ISO equivalent 64; Focal Length (35mm) 212. Bottom same except - Exposure Time 0.0027s (1/366); Aperture ƒ/6.3; Focal Length (35mm) 37