By Lisa Cohen, Colorado Master GardenerSM, and Carl Wilson, Horticulturist, Colorado State University Cooperative Extension
With their great variation in size and long season of bloom, campanulas are deservedly popular flowers in both borders and rock gardens.
The campanula, commonly known as bellflower, is a genus of about 300 species of annuals, biennials, and perennials. The attractive bell or star-shaped flowers are white, blue, purple and occasionally rose, as in the case of C. medium, Canterbury Bells.
Three popular perennial species that perform well along the Front Range are Campanula cochlearifolia (Dwarf bellflower), C. rotundifolia (Scotch bluebell), and C. carpatica (Carpathian harebell).
Dwarf bellflower, a compact plant that can be used as a groundcover, grows 3 inches tall and 15 inches wide. "Bavaria Blue" is an improved selection with sky blue flowers; "Alba" bears white blooms. Flowers are produced on short, wiry stems and in cooler situations, bloom may continue throughout the summer.
This bellflower will spread gradually and fill in empty spaces between other plants and around rocks. Dwarf bellflower requires filtered shade all day but will tolerate morning sun if plants receive afternoon shade. It is hardy for zone 5 Front Range and plains gardeners and is worth trying in zone 4 foothill areas.
Scotch bluebell grows wild in Colorado and other places in the U.S. but is really native to the British Isles. It grows 10 inches tall and 15 inches wide and produces nodding blue flowers on a series of wiry stems. Several varieties are available,including white "Alba." This charming flower produces concentrated bloom in June and July with some bloom continuing through into October along the Front Range.
This species is hardy for zone 3 mountain gardeners. Several cultivars of Carpathian harebell are locally popular, including "Blue Clips" and "White Clips." These compact plants, 6 to 12 inches tall and up to 20 inches wide, can form a ground cover and make an excellent border edging. The open flowers are upturned and plants bloom primarily in July with more blooms through the summer to the first frost.
Plants are hardy in zone 4 and 5 and may be tried in zone 3. The above varieties of campanula are all considered beauties, but the beast with the same name, creeping bellflower, (C. rapunculoides) has escaped from older gardens to become a weed. It is a perennial, 2 to 4 feet tall, and spreads by deep roots. The erect stem is often purplish. Leaves are somewhat rough and lance-shaped, tapering to a point. The 1-inch flowers are purple, down-turned and bell-shaped. Plants can spread by seeds and creeping roots and thrive in sun or shade. It can become a serious weed problem in urban areas as well as in pastures and open fields.
Most species of bellflower are easily cultivated from seeds or cuttings, and provide a long flowering display, particularly if deadheaded. Many will benefit from cutting back in later years.
Campanulas grow best in good garden soils with regular watering. This is a cold hardy perennial that is particularly useful to Colorado gardeners.
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010