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When they are young, sunflowers follow the Sun. Every morning, they face east to catch the first rays of sunlight, and by the end of the day, they face west to the sunset. At night, they bend back ready for the next morning’s light.

Some scientists from the United States wanted to know what was going on. Do sunflowers just follow the Sun, or do they have an internal clock, telling them when to turn?

In one experiment, they raised sunflowers to track the Sun. Then, they moved the plants into a room where there was light all the time. For several days, the sunflowers kept moving back and forth, trying to follow the Sun.

Investigating further, they set up a lab with an artificial sun of moving lights. They raised some sunflowers on a 24 hour day, and then used the artificial sun to simulate a much longer, 30 hour day. Rather than moving smoothly, the sunflowers moved much more erratically – they had jet lag! When they set the artificial sun back to a 24 hour day, the plants quickly adjusted and moved as normal once again.

These two experiments showed that sunflowers have at least two ways of telling time. They react to the Sun moving through the sky, and they also have an internal clock which keeps them running on a 24 hour day. In everyday life, far from meddling scientists, these two systems make sure growing sunflowers get all the sunlight they need to grow tall and strong.

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