Some flowers open only once, as they grow from a bud to a full-blown blossom. Tulip flowers are different. On sunny days with cool nights, the tulip flower can open and close right before your eyes!

Tulip plants are sensitive to sunlight and temperature. As morning temperatures increase, tulip flowers open. By mid-day, insect pollinators are out looking for flowers. Insects visit the colorful yellow and purple parts inside the open tulip flower, and pollination can occur.

As nighttime approaches and temperatures decrease, tulip flowers close. The closed petals protect the inside of the flower from cold temperatures and unwanted insects.

Internal signals also determine when some flowers open and close. A 24-hour cycle of opening and closing is controlled by the plant’s biological clock. This activity is known as a plant’s “circadian rhythm.”

Now each spring as you observe the opening and closing flowers of the tulip plant, you will know that both the environment (sunlight and temperature) and the plant’s internal rhythm work in harmony to make it happen.

Word Bank

temperatures

rhythm

sunlight

pollination

cycle

open

close

increase

harmony

flower

environment