Why sunflower turns towards sun

Skip to content Search for: Search Close. Close Menu. There's been advances in knowing how sunflowers track the sun, but botanists are still arguing over why. And, to make things confusing, they could all be right. Warming Experiments with heating flowers showed that warm flowers got more visits from pollinators. Visibility If sunflowers face east, then their heads are illuminated by the morning sun.

The results were published Aug. While sunflowers are growing, their heads turn back and forth to track the sun during the day. Previous work from Harmer's lab showed that this tracking is controlled by the plant's internal circadian clock.

But as the flower heads, or capitula, mature and their stems become stiff and woody, this movement decreases until the heads are all facing the morning sun. When postdoctoral researcher Nicky Creux changed the orientation of sunflowers by turning their pots around, she noticed that east-facing flower heads attracted a lot more bees, especially in the morning, than plants facing west. In a series of experiments, Creux, Harmer and colleagues found that the east-facing heads were significantly warmer in the morning than west-facing flower heads.

That warmth brings an energy benefit to foraging bees early in the morning, Harmer said. Direct sunlight also lights up ultraviolet markings on the flower petals that are visible to bees but not to human eyes. A sunflower is actually a composite of hundreds, sometimes thousands, of individual flowers. These individual florets develop first at the outer edge of the flower head, forming characteristic spiral patterns.

The orientation of the plants also affected flower development and reproductive success. East-facing plants tended to produce larger and heavier seeds. When plants become wilted in the absence of enough rainfall or irrigation, their turgor pressure drops, and they wilt. Wilted plants resume heliotropic movement when they become hydrated again, and plants with waterlogged cells resume heliotropic movement when the soil dries sufficiently and their moisture level stabilizes.

Greenhouse-grown sunflowers that have fixed overhead lighting instead of access to sunlight do not exhibit heliotropic movement. Because of this, scientific studies conclude that heliotropism is possible only with a light source that moves. 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.