Photoperiodism

How do plants know exactly when to bloom or shed leaves? They don’t need a calendar—they track the seasons naturally.

Plants respond to changes in the length of day and night, a process called photoperiodism.

They use special light-sensitive chemicals to measure how long they have been in the dark.

When the timing is right, plants bloom, shed leaves, and form buds to survive seasonal changes.

Based on photoperiodism, flowering plants are classified into two main types: short-day plants and long-day plants.

As fall approaches, the days become shorter, and nights grow longer. Plants, like poinsettias and Christmas cacti, bloom when nights are longer.

These are called short-day plants because they bloom when daylight is shorter than a certain number of hours. Other short-day plants include cotton, rice, and chrysanthemums.

In contrast, some plants need longer days to flower. Crops like wheat and lettuce grow better when there’s more daylight in spring and summer.

These are called long-day plants because they need more daylight hours to bloom. Other examples include spinach, clover, and turnips.