Whether you're a new gardener or one with lots of experience, you might not know that some plants close their flowers at night. Although the reason for this behavior isn't fully understood, it may have to do with the habits of insects that visit the plant to spread pollen. Flowers may only stay open in the daytime because this is when the particular insects that visit them are active; closing at night may also protect the pollen from unwanted pests. And it may not be the absence of light that prompts this behavior, but a built-in clock that governs the plant's behavior. Whatever the reason, it can be interesting and entertaining to grow a few plants that close up their flowers on a nightly basis, and there's a good-sized group from which to choose.
A number of plants that usually grow as annuals are recognized for their habit of closing up their flowers at night, then reopening them the following morning.
The morning glory (Ipomoea purpurea) is one example that grows as a climbing vine, sometimes up to 10 feet tall. It loves full sun, where it produces showy, trumpet-shaped purple flowers that have striking white throats. Each flower opens in the morning, then closes in the afternoon, to open again the next day.
The gazania plant (Gazania longiscapa), also known as African daisy, has unusual, brightly colored, daisy-like flowers, with each petal striped in yellow, orange, maroon and other colors. It thrives in hot, dry areas that get strong sun and also opens and closes its vivid blossoms with the arrival and departure of the sun.
The moss rose (Portulaca grandiflora) is another example of a plant in this group of annuals. It gets its name from its showy flowers that resemble old-fashioned roses and come in many colors. A succulent plant with fleshy narrow leaves, it's about 6 inches tall and thrives in hot, dry conditions, spreading to cover up to 2 feet.
Some perennial plants that die to the ground during winter -- called herbaceous perennials -- also have the interesting habit of closing up their flowers at night.
The bloodroot plant (Sanguinaria canadensis) is a good example that belongs to the poppy family, with poppy-like, single white blossoms on 4-inch-tall stalks. These close each night or on cloudy days. It's a native plant in parts of the United States and grows as a garden perennial in U.S. Department of Agriculture plant hardiness zones 3 through 8.
A perennial plant called spring beauty (Claytonia virginica) that has lavender flowers with distinct purple veins also closes up its attractive flowers each night. A perennial wildflower in parts of the United States, it's about 6 inches tall and grows best in moist, partly shaded locations. Spring beauty thrives in USDA zones 3 through 8.
The California poppy (Eschscholzia californica) is another interesting plant whose flowers close up each night, to re-awaken the next day. It's often used as an annual, but can also grow as a short-lived perennial in USDA zones 5 through 10. It has intensely colored flowers with delicate, thin petals that appear all summer long in orange, red or yellow.
A few types of night-closing flowering plants are woody shrubs or trees.
The Rose-of-Sharon plant (Hibiscus syriacus) grows as a woody shrub that's usually about 8 feet tall and 4 feet wide, with large, trumpet-shaped flowers in many colors, depending on the variety. These usually close up each night and reopen the next day, although a few cultivars, such as 'Diana' (_Hibiscus syriacus '_Diana') keep their flowers open around the clock. Rose-of-Sharon grows in USDA zones 5 through 8.
A native American tree called the southern magnolia (Magnolia grandiflora) has a slightly different habit; it opens its impressive white flowers each morning at about 9 a.m., then closes them at night, doing this for about three days. On the last night, flowers shed their stamens, then reopen the next morning to turn brown and die back. This tree grows in USDA zones 7A through 10A.