Perennial flowering plants are those that usually live more than two years. As long as they are regularly watered, fertilized and, in some cases, protected from cold, perennials continue to provide their annual bursts of flower color year after year. Although a large number of plants are flowering perennials, only several of them are among the most common in gardens.
Black-eyed Susan (Rudbeckia fulgida), such as the cultivar Viette's Little Suzy (Rudbeckia fulgida 'Blovi' Viette's Little Suzy), has bright-yellow blooms with dark-brown to deep-purple centers. The leaves are medium green and range from oblong to spearlike. Viette's Little Suzy averages 1 to 1 1/2 feet in height with a spread of up to 1 foot and is often used as a border plant or in themed gardens. It thrives in a full-sun site, blooms from July into September and tolerates drought, dry, clay and shallow rocky soils, polluted air and deer. Butterflies are attracted to this plant's flowers. It is perennial, or hardy, in U.S. Department of Agriculture plant hardiness zones 3 through 9.
The purple coneflower (Echinacea purpurea, USDA zones 3 through 8) is a native of eastern North America. The hardy plant is tolerant of deer, drought and poor soil, as long as the soil is kept moderately moist and well-drained. This perennial does best in full sun to partial shade and is low-maintenance. Its flowers are purple-pink, have a reddish brown center and are up to 5 inches wide. It blooms from June to August, attracting birds and butterflies. Purple coneflower averages a height of 2 to 5 feet and a spread of 1 1/2 to 2 feet.
A hybrid created by Luther Burbank in the 1890s, the Shasta daisy (Leucanthemum x superbum) is named for Mount Shasta in northern California. The Shasta daisy cultivar 'Aglaia' (Leucanthemum x superbum 'Aglaia,' USDA zones 5 through 9) prefers full sun and can grow up to 2 feet tall and have a spread of up to 1 1/2 feet. It flowers from July to September and attracts butterflies. Each bloom has white, fringed petals surrounding a yellow center and sits atop a stiff stem. The cultivar's foliage is medium to dark green with rough-edges and up to 15 inches long. 'Aglaia' tolerates dry soil, drought conditions, rabbits and deer. It does not produce seeds that result in new plants.
A lupine hybrid (Lupinus x hybrida, USDA zones 4 through 8) is a crossbreed of the wild species plant. It prefers full sun except where summers are hot; there it thrives with a bit of shade during hot afternoons. The plant grows best in the Pacific Northwest, across the northern United States and in New England. Lupine can grow up to 4 feet tall with a spread of up to 1 1/2 feet. Small flowers grow in clusters at the end of its tall stalks and are white, red, pink, yellow, blue, purple or bicolor. The blooms appear from May to July and are attractive to butterflies.
Although lupine is a perennial, it works best as an annual in areas of the U.S. South that experience high humidity.
The alpine aster (Aster alpinus, USDA zones 5 through 7) originated in North America, Europe and Asia. Looking much like small daisies, its blue-violet flowers with yellow centers grow in clusters atop the plant that can grow 1 foot tall. This natural butterfly attractant blooms from May through June. A low-maintenance perennial, it thrives with full sun and a moderate amount of water. It is drought-tolerant and does well in shallow, rocky soil. Alpine aster is often used in borders and rock gardens.
Possessing blooms that range from pastel pink to yellow, the rock rose (Helianthemum nummularium, USDA zones 5 through 7) is often used as ground cover, in rock gardens and as a border plant. Its flower appear from May to June and are open for only one day. In the right conditions, the blooms, which have five petals and are roughly 1 inch across, may cover the entire plant. Rock rose's lancelike leaves, growing 1 to 2 inches long, are gray-green. The plant grows up to 1 foot tall with a spread up to 3 feet and is drought-tolerant. It prefers full sun, cool summers, warm winters and a dry climate.
While rock roses grow in USDA zone 5, they usually need to be brought inside or covered during the colder seasons.