Annual plants add quick color to Ohio's U.S. Department of Agriculture Plant Hardiness zone 5 through 7 gardens. They are useful in filling those gaps in perennial beds. Annuals are planted after the danger of frost has passed, usually in mid-to-late May in Ohio, and last until the first frost. Such plants are vigorous growers, spread quickly and bloom almost continually all season.
Annual geraniums, botanical name Pelargonium, are native to southern Africa, but have become a favorite of Ohio gardeners. These plants thrive in full sun and produce large, showy white, red, pink or orange blossoms throughout the growing season. Mature plants grow to around 24 to 36 inches high and benefit from pinching back new branches.
Unlike the other plants mentioned here, impatiens thrive in shady spots. There are more than 800 species of impatiens and new hybrids are introduced each year. Most impatiens are low growing--24 inches high or less at maturity--and produce delicate, paper-thin blossoms in white, pink, red, orange and lavender. Some species have variegated leaves and others have double blossoms.
Begonia is a genus of more than 1,500 species. These sun-loving plants are native to tropical climates, including parts of Central and South America, but are widely grown as annuals in Ohio and other parts of the Midwestern United States. Begonias are broad-leafed plants that produce small rose-like blossoms in a variety of colors, including white, pink, orange and red. They prefer full sun and frequent watering.
Marigolds, genus name Tagetes, seem to find their way into most every Ohio garden. These plants, native to Mexico and South and Central America, thrive in full sun and are easy to grow. Marigolds produce round blossoms in orange and yellow hues. Said to be a deterrent to insects, Marigolds are commonly planted in or near vegetable gardens. Mature plants grow to be 6 to 12 inches tall.