A stem that grows crooked on purpose
Why Do Sunflowers Follow the Sun?
A young sunflower turns to face the sun all day, and it does it by growing unevenly rather than by moving.
-
Step 1 of 5
Plants have no muscles, so they grow instead.
A plant changes direction by making one side of a stem grow longer than the other. The stem bends because it is now uneven, not because anything pulled it.
-
Step 2 of 5
The shaded side grows faster.
A growth hormone collects on whichever side is in shadow and makes those cells stretch. The longer side pushes the stem over until the head points at the light.
-
Step 3 of 5
At night it winds back.
The plant reverses the growth overnight so the head is already facing east before sunrise. It is running on an internal clock, not just reacting to light.
-
Step 4 of 5
Mature flowers stop and face east for good.
Once the head is heavy with seeds the stem stiffens and tracking stops, permanently pointing east. A field of open sunflowers all faces the same way.
-
Step 5 of 5
Facing east is a decision about bees.
An east-facing head warms up early in the morning, and a warm flower gets noticeably more insect visits than a cold one. Warmth in the morning is worth more than light all day.
The spiral of seeds in the head follows the same numerical pattern as pine cones and pineapples, which packs the most seeds into the space.
The short version
A young sunflower turns by growing faster on its shaded side, and a mature one locks facing east to warm up for the bees.
Try it yourself
Put a seedling on a windowsill and turn the pot around. Within a day it has bent back toward the glass.