Why sunflower faces sun

Scientists hypothesize these circadian rhythms—behavioral changes associated with an internal clock—explain sun tracking in young blossom s. How does the full cycle wor k?

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 east ward to start the cycle again. In other words, the east side of their flower stems expand from m orning to evening , allowing the bloom to turn from east to west. But at night, the west side of each flower stem grows more rapidly , resulting in a return to the eastward facing position for the dawn. As sunflowers mature, this process comes to a halt. 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. 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. They also released pollen earlier in the morning, coinciding with the times when bees visit. These effects seemed to be controlled by the temperature at the flower head.

When researchers used a portable heater to warm up west-facing heads, they were able to get similar results to east-facing flower heads. Finally, Evan Brown, an undergraduate student supervised by Ben Blackman at the University of Virginia, took sterile male plants, which could produce seeds but not make pollen, and surrounded them with normal plants facing east or west. Using genotyping, they were able to distinguish whether the male-sterile plants were pollinated by east- or west-facing plants.

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.