Why do sunflowers follow the sun?

Why do sunflowers follow the sun?  

​Good morning.  Another awesome day to be working in the greenhouse and outside.  How about you?  Do you get a chance to work in your garden this weekend? I know you have weeding to do, and then watering.  It is lots of work to keep up the garden, flower beds, and containers.  Good job that you do.  Hope you can enjoy all of your hard work.  I enjoy all of the wagons full of plants and then realized I was part of having them grow so well.  I need to thank the gals that help me plant.  They get to see them little, but hope when they see the pictures or come by they are proud of what they did.  We grow most of what you see.  We buy some annuals, herbs and trees and shrubs in perennials.  But all the rest we grow out of this greenhouse.  I have been doing this for 37 years.  But I am always learning something.  What I post about today is that I learned about the sunflowers but didn’t know what it was called or why.  Enjoy the day, stay safe.
 
Australia family and friends for their Tuesday will have a high of 66F(16C) while we have a high of 77F(25C).  But as I write this post at 9:30 AM we have a temperature of 68F.  Almost similar weather.  They have rain predicted so stay dry, warm, and safe. 
 
This is a pot of sunflowers that I had the 4-Hers plant.  The large pots serve two purposes.  They hold up the trees, so they don’t fall.  Also they will go to the Franklin Co Fair.  I will enjoy them all season long.  Great job 4-Hers West Fork Winners.  But I need to move the sunflower pot as the stems only get the east sun, so they are turned all day long. 
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Sunflowers track the sun through a process called heliotropism, using differential stem growth and circadian rhythms to maximize sunlight exposure.
How Sunflowers Follow the Sun
Young sunflowers exhibit heliotropism, turning their heads from east to west during the day and returning east at night in anticipation of sunrise
This movement is driven by differential growth: the east side of the stem elongates faster during the day, bending the flower toward the sun, while the west side grows faster at night, swinging the head back east
 This daily cycle is regulated by the plant’s internal circadian clock, allowing the sunflower to anticipate the sun’s position even under constant light conditions
Biological Mechanisms
Phototropism: Sunflowers grow toward light, a general plant response that contributes to heliotropism
Plant Hormones: Auxins promote cell elongation on one side of the stem, enabling the bending motion
Turgor Pressure: Water distribution within the stem can also influence curvature, supporting the head’s movement
Advantages of Sun Tracking
By following the sun, young sunflowers maximize photosynthesis, capturing more light energy for growth and development
 This behavior also helps coordinate floret opening with pollinator activity, enhancing reproductive success
Mature Sunflowers
Once the flower blooms, the heliotropic movement generally stops, and the flower permanently faces east
This may be due to the weight of the mature flower head or a diminishing circadian rhythm, though the exact reason is still under study
Summary
Sunflowers’ sun-following behavior is a sophisticated combination of differential stem growth, circadian rhythms, and hormonal regulation, primarily observed in young plants. This adaptation optimizes sunlight capture, supports photosynthesis, and improves reproductive success, while mature flowers remain fixed facing east.
Till next time this is Becky Litterer , Becky’s Greenhouse, Dougherty Iowa [email protected]  641-794-3337  cell 641-903-9365  Beckysgreenhouse.com  Facebook Becky Kerndt Litterer or Becky’s Greenhouse