The familiar idea that sunflowers follow the Sun is partly right.
Young sunflowers really can track it across the sky.
Mature flower heads usually stop.
Young sunflowers use heliotropism
This Sun-tracking movement is called heliotropism.
During the day, growth on one side of a young stem differs from growth on the other.
That causes the plant to bend gradually from east toward west as the Sun moves.
The plant resets overnight
At night, the growth pattern reverses.
The young plant turns back toward the east before sunrise.
Then the daily tracking cycle can begin again.
Mature flower heads usually stop following
Once the flower is fully developed, the stem becomes less flexible.
The mature head generally settles facing east rather than continuing to sweep across the sky every day.
So the classic image of every sunflower turning all day long is too simple.
Why face east?
The recorded script notes that an east-facing flower can warm earlier in the morning.
That extra warmth may make the flower more attractive to pollinating insects.
The plant’s final orientation can therefore have a biological advantage.
Is this about photosynthesis?
Young leaves and stems certainly benefit from light.
But the famous movement of the flower is tied to growth patterns and daily timing.
The same plant world is also why grass looks green because of chlorophyll, but chlorophyll alone does not explain sunflower tracking.
Do all sunflowers behave exactly the same way?
No biological behavior is perfectly identical in every plant.
The useful general rule from the source is this:
Young sunflowers track the Sun.
Mature heads usually settle facing east.
Apparently even sunflowers eventually decide they are done turning around all day.
And that’s the short explanation.
Related explanations: Why is grass green?, Why do flowers smell?, and Why do pine trees stay green in winter?