You may have noticed that some sunflowers face a different direction by the end of the day.
Sunflowers can grow in all 50 states. They thrive in environments where they can receive six or more hours of direct sunlight, so naturally, sunflowers prefer the longer lit days of summer.
Sunflowers can survive in extreme heat, but they grow best in temperatures between 70 to 78 degrees. Not only that, but sunflowers can tolerate periods of drought as long as they receive enough water while their roots are growing.
Speaking of growth, you may have noticed newer sunflowers tend to move more compared to older sunflowers. So, why is that?
At dawn, all sunflowers will start off the day facing east, getting ready for the sun to emerge over the horizon. As the sun moves across the sky as the day goes on, only the younger sunflowers will follow along and pivot to the west.
Once the sun sets in the western sky, those young sunflowers will slowly turn back to east during the night, waiting for the sun to rise once again.
This sun tracking movement is known as heliotropism, and it happens less as sunflowers grow older. Once the sunflower matures, it stops following the sun and just stays facing east.
Back in 2016, a study was published which revealed how sunflowers’ own biological clock, ability to detect light, and the flower’s genes allow the stems to bend with the arc of the sun.
The study detailed how sunflowers have their own 24-hour circadian rhythm, or internal clock. Sleeping at night and being awake during the day is an example of that for people, and following the sun is the circadian rhythm of young sunflowers.
Unlike humans though, sunflowers don’t have muscles, so how are they turning in the first place to follow the sun on cue? That answer comes down to their stems.
The stems of young sunflowers grow more during the night, but only on the west side which allows the sunflower head to bend eastward. During the day, the stem’s east side grows, resulting in a swaying motion to the west with the sun.
As the sunflower matures, that overall growth starts to slow down. Essentially, the older plants settle on facing east as it reacts more strongly to light early in the day than later on, so it gradually stops moving.
There is an important advantage towards sunflowers facing east. By already facing that direction as the sun rises, that gives the flower a head start on warming up, which will, in turn, attract more pollinating insects, like bees.
When researchers compared mature flowers facing east all day to those that turned west, they found that the stationary blooms attracted upwards of five times more pollinators.
If you find yourself at one of the local sunflower fields as dusk nears, see how many younger blooms you can pick out as those sunflowers look towards the setting sun in the west.