Why Sunflowers Always Face The Sun: Solved!

We’ve probably all heard the fact that sunflowers follow the sun, it’s something which gives these beautiful plants their name. The question you may be asking at this point is why sunflowers always face the sun?

First lets unpack this idea a little. The idea that sunflowers always track the sun is a little bit of an exaggeration. It’s only the young the flower heads that track the sun before they fully bloom. Once the sunflower reaches maturity it then fixes into a single position and faces east permanently rather than following the sun across the sky.

While mature sunflowers no longer face west at all, therein lies another mystery. Why do the sunflowers stop following the sun once they’re all grown up? Let’s look at what happens in more detail:

Why sunflowers follow the sun before they reach maturity:

The reason for this behaviour from the young flowers actually comes from a common behaviour amongst plants (and people in fact). Flowers follow a circadian rhythm (or a 24 hour rhythm) meaning that they are attuned to sense changes in light and temperature as the day progresses. As our days are based entirely on sunlight and the movement of the sun, life normally conserves its energy by being active during the day and being dormant during the night.

In this case, sunflowers follow a behaviour called helitropism, which is made possible by the plant elongating its stem throughout the day. This itself is made possible by growth hormones in the plant which react to heat and light, which is a behaviour built into the genetics of the plant. The reason sunflowers do this is simple. The brown face of the plant contains numerous tiny flowers (rather than the sunflower being simply one big plant) and to ensure that the whole plant can develop properly they need the maximum amount of sun possible. As Atamian, Hagop S., et al. comment: plants that had this movement disrupted led to ” ~10% decreases in both dry biomass and leaf area”.  Simply put without this behaviour the plants wouldn’t grow properly, or to their fullest extent.

Why do mature sunflowers only face East?

You might be wondering at this point why sunflowers continue to face towards the morning sun when they’ve fully bloomed and no longer need such high sunlight levels. The answer to this is also interesting. It’s believed that this is due to the fact that bees prefer warm flowers, according to a study by UC Davis. This allows the mature plants to cross pollinate with neighbouring flowers much easier.

Key facts about sunflowers:

• They originate in the Americas
• They can grow to over 30 feet tall
• The sunflower head is actually 1000-2000 flowers joined at the base
• They are the national flower of Ukraine
• A sunflower can contain up to 2000 seeds

It’s hard to say if anything loves the sun as much as a sunflower, but we’re pretty sure that this is the ideal flower for someone who loves the summer. Do you enjoy sunflower season as much as we do? Tell us in the comments!

Send warm smiles this season with our summer collection. FloraQueen is able to deliver to over 100 countries around the globe, so no matter where you or your friends and family are spending the summer you can share a beautiful surprise of fresh flowers.

Citation

Atamian, Hagop S., et al. “Circadian Regulation of Sunflower Heliotropism, Floral Orientation, and Pollinator Visits.” Science, American Association for the Advancement of Science, 5 Aug. 2016, science.sciencemag.org/content/353/6299/587.full.