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Most flowers open only once, as they grow from a bud to a full-blown blossom. Others open during the day and close at night, some at varying times of the day. In harsh environments, this adaptation can help flowers conserve energy and improve the health of the plant as a whole.

Diurnal and Nocturnal Flowers

Some flowers, called diurnal, close during the night, while nocturnal flowers close during the day and open at night. Diurnal flowers close to keep insects out at night and protect the delicate blossoms for daytime reproduction. Nocturnal flowers, including some cacti and bromeliads, close during the day to avoid harsh sunlight and open during the night to pollinate. Diurnal flowers are typically pollinated by butterflies, bees and other creatures awake in the day, while nocturnal blossoms may be pollinated by moths or bats.

The Process

Flowers that open and close can do so in one of two ways. Some flowers, including those in the genus Kalanchoe, grow new cells each day on the inside to open the flower and on the outside to close the flower blossom. Other flowers open and close by expanding cells on the inside and outside of the flower by pumping water in and out of the cells. Light, temperature and even internal clocks can trigger these changes in flowers. ProFlowers’ Year of Seeds allows you to witness this phenomenon with several different flowers, including marigolds and poppies.

Changes in the Flower

While some blossoms just open and close, others change shape in response to light or warmth. Bulb flowers, including tulips and crocuses, grow faster on the upper side than the lower, encouraging the bloom to open wide in the morning. In the afternoon, the lower side of the bulb expands, creating a cup-shaped flower. Potted bulb gardens in the house, like the ProFlowers’ Pretty in Pink Bulb Garden, may show the same effect, especially if you adjust the temperature in your home from night to day.

Opening Cut Flowers

If you have a bouquet with closed buds rather than open flowers, you may want to open the blossoms to create a prettier display. Cut the stems on an angle when you purchase the flowers, and place them in warm water to encourage the flower to absorb water. Use a low temperature hair dryer to mimic the warmth of the sun and help the blossoms to open up in the vase.