Glorious sunflowers (Helianthus annuus) look bright and happy no matter what direction they face, but a new study confirms that east-facing sunflowers are healthier, happier, and more fruitful than those facing any other direction.
New research shows this is because light and warmth from the early morning sun after sunrise attracts more bees. Sunflowers enjoy more abundant seeds, better growth, earlier pollen production, and greater success at reproduction.
HELIOTROPISM is the term given to the fascinating phenomenon of flowers turning to follow the sun across the sky. This is possible due to the plant’s circadian-type rhythm, which allows it to react to changes in roughly 24-hour cycles.
This is usually a habit of younger flowers, which turn their heads to follow the sun from sunrise to sunset. They can do this while their stems are supple. As young flowers, they have green lion-mane-like ‘bracts’ and leaves just below the flower that face the sun, so by following the sun, photosynthesis is maximized.
This 1:00-minute video by UC Davis shows bees visiting east and west facing sunflowers:
In 2016, plant biologist Stacey Harmer of the University of California, Davis, published a research article in Science. Harmer and colleagues found that sun gazing helped flower and plant growth as well as helping them to attract more pollinators. Controls were performed on east-facing and west-facing sunflowers and artificial light tests were done.
Sunflowers practice heliotropism because their stems lengthen in different ways at different times of day. This unequal growth on both sides is due to Auxins, or plant hormones that stimulate growth. As sunflowers mature, the stalks harden and get less flexible, so the sunflower has less mobility. That is when it turns to permanently face east.
A team led by UC Davis biologist Nikki Crooks performed further research as they devised an experiment to find out why sunflowers face the sun. Their first observation was that the east-facing sunflowers released a lot of pollen early in the morning as the sunlight warmed the flower heads. This was right at the time of maximum pollinator visitation, and this attracted many more bees in the morning. The bees were ambivalent throughout the rest of the day, so the morning sunlight window made a huge difference.
This 4:02-minute video by Science ABC shows how sunflowers face the sun:
Since each sunflower plant only has one flower head, and this is the flower’s only way to reproduce, the need to get the attention of pollinators is urgent. The east-facing flowers warm up quickly and this attracts bees and other insects.
This is a very effective survival strategy for sunflowers. Researchers made the remarkable discovery that plants facing east attract five times more pollinators than plants facing west.
This new research has been recently published in New Phytologist and you can read the article here.