It has long been known that young sunflowers bend their growing shoots to follow the sun’s movement from east to west during the day, bending back to the east again to be ready for the new day. It was thought that this was simply the plants following the light, but careful experimentation has shown that this is not the case. When outdoor-grown sunflowers were moved into an indoor growth chamber with a fixed overhead light, the plants still bent back and forth to track an imaginary sun for several days, indicating that the movement was driven by an internal clock. To find out how movement affected the growth of plants, the researchers staked sunflowers so they were unable to move. These immobile plants grew to be smaller overall, indicating that tracking the sun gives them a growth boost.
Fully grown sunflowers do not track the sun, but instead always face east to catch its morning rays. This helps the flowers heat up more quickly, attracting many more pollinating insects.