Fringed bleeding heart is a shade-tolerant plant that will also thrive in cool morning sun. (Photo by Sandra Leavitt Lerner/FTWP/PHOTO BY SANDRA LEAVITT LERNER/FTWP)

Some gardeners prefer natural sweeping lines. Others like formality. Yet the perennial herbaceous flowers that we enjoy in the summer months continue to be a constant in both styles of landscape design, adding a burst of color to the garden.

Perennials also offer great flexibility.

Most can be moved around, allowing for trial-and-error landscaping without sacrificing the plant. Combinations that clash can be easily separated. Plants that don’t thrive in one location can be moved to another. Good times for transplanting or dividing most perennials are fall or early spring. Fall blooming flora — including hardy chrysanthemum, autumn joy sedum, New York ironweed (Vernonia noveboracensis), aster and boltonia — are moved around in early spring because they flower in fall.

Perennials also can be planted at various times, depending on their hardiness and blooming schedule. Marginally hardy plants such as rose verbenas or cupflowers (Nierembergia) should be planted in early spring so they do not freeze before they have had a growing season in which to establish themselves.

Here is a list of the most dependable perennials we have grown that have returned for many years:

• Chinese astilbe is primarily represented by a hybrid named “Pumila.” It’s a long-lived dwarf hybrid that likes moist soil and protection from hot sun. There is considerable variation in height from one “Pumila” to another. It can grow eight inches tall and serve as a ground cover or edging plant, yet in the same planting there can be some growing up to 21 / 2 feet tall.

• Gayfeather (Liatris spicata) is a native plant that covers the prairies in the Midwest and produces a profusion of flowers when planted in moist soil in the South. It’s just beginning to flower in the Washington area. The purplish/pink-spiked flowers open from top to bottom

• “Husker Red” penstemon has maroon to purple foliage in cool temperatures and deep green in hot, humid areas. It’s a native plant from Maine to South Dakota and Oklahoma to Virginia south to Florida. The pink-edged white flowers open in late spring or early summer.

• “Coronation Gold” yarrow is a long-lived perennial with yellow flowers three to four inches in diameter on strong branches that don’t require staking. Flowers can last eight weeks or longer.

• Moonbeam coreopsis has ferny foliage and a dainty appearance It is a drought-resistant, dependable and long-blooming member of the daisy family with pale yellow flowers about one inch in diameter. It requires little maintenance, prefers full sun and grows in most soils. Its lacy foliage topped with flowers from June to September provides ornamental value the entire season.

• Narrow-leaf blue star (Amsonia hubrichtii) has textured foliage that creates a standout in sunny protected locations. It has blue flowers in spring and green foliage in summer that turns yellow in fall, adding interest to the garden.

• Most indigos (Baptisia) are small flowering native shrubs when they have consistent moisture and full sun. They flower early in the season – blooming yellow, white and purple.

• Rose turtlehead (Chelone obliqua) is a native plant in low-lying areas from Maryland to Minnesota, south to Georgia, Mississippi and Arkansas. It grows in open woodland and along forest edges, reaching two to three feet in height. Turtle-head’s pink flower buds open in late July and continue to bloom into late fall.

• Fringed bleeding heart (Dicentra eximia) is native to the eastern United States from the mountains of New York south to West Virginia, Tennessee and Georgia. It grows 18 to 24 inches tall from a rhizomatous root. The light airy shrub is a shade-tolerant plant that will also thrive in cool morning sun. Leaves have deeply cut, fern-like foliage, and red, pink or white flowers in early summer. Deadhead flowers after they bloom to keep them from going to seed. Seedlings can be pulled to control spread of the plant.

• Kim’s knee high purple coneflower (Echinacea purpurea “Kim’s Knee High”) has a tight growth habit with handsome purple flowers in summer. This dwarf hybrid grows 12 to 18 inches tall. It won’t become invasive and will return dependably once established.

• Aster is usually considered a fall blooming plant, but the fragrant hybrids called “Monch” and “Wonder of Staffa” bloom for about three months, from early summer into fall with lavender petals and yellow centers. It makes an excellent cut flower. With well-drained, moist soil and good air circulation, these members of the daisy family will grow two feet tall with mounds of flowering stems that should not require staking.

• Black-eyed Susan creates a splash of bright yellow petals surrounding a black-brown center in July and August for a month or more. It’s the state flower of Maryland, drought tolerant and forgiving of most soils. But it needs full sun. The centers persist after the petals fall. Some gardeners like this ornamental look and allow plants to stand well into fall.

• Stella d’Oro daylily is compact —18 inches tall — with an impressive profusion of yellow flowers. It pushes a second flush of buds and blooms into autumn, offering floral and foliage interest from June to September. It loves moist, well-drained soil and will tolerate some shade with fewer blooms.

Unlike annuals, which bloom all summer, perennials have a specific blooming season. Plant accordingly, with enough variety to coordinate them so you have flowers all season. The perfect combinations will delight your senses year after year.

Joel M. Lerner is president of Environmental Design in Capitol View Park.