Why Do Some Flowers Close up at Night?
Flowers close their petals at night because they are protecting the pollen and other reproductive parts of the plant that are inside from the cold and rain. Also, many flowers are pollinated by insects and birds that are active during the day, so there is no reason to be open at night.
However, some types of flowers, tropical fruit plants, varieties of cactus flowers and related plants are pollinated by bats at night, and these flowers will be open at night and closed during the daytime.
Many flowers open and close their blossoms with the rising or setting of the sun. Such sleep movements are caused by a special kind of cell in the petals which react to light changes.
At night, the lack of sunshine causes the cells to lose some of their water. The cells shrink, causing the petals to close up. The next morning, the cells again fill with water, allowing the flower petals to open.
Some flowers, such as the moonflower, night-blooming jasmine, evening primrose, angel’s trumpet, night phlox, and the night-blooming cereus, reverse this procedure. Their blossoms remain closed during the day and open only at night reacting to light or temperature changes.
Flowers, such as tudaylilies, remain open for twenty-four hours. Other flowers have unusual opening and closing habits. Crocuses, poppies, and morning glories, for example, open as the temperature increases during the day and close as the day gets cooler in the late afternoon.
The flower called the four-o’clock closes in the morning and opens again late in the afternoon, right around four o’clock. Some plants also react to touch and close up their leaves and “play dead” if a hand or twig brushes against them. For example, if you touch a mimosa plant, it will fold its leaves and the stalk will droop.