From large, delicate nodding bells to tiny cups on weedy stalks, campanulas represent a wide range of species defined mostly by the pretty shape and blue or white shaded blooms. Grown in a wide range of climate zones, campanula prefers partial shade and cool roots. Perfect as a border plant or for rock gardens, it will spread and quickly fill in areas with plenty of pretty summer color.
Campanula carpatica, known as Carpathian Harebell or bellflower, has well defined, broad bell-shaped flowers with white or bright blue blooms. Growing in a mound that will top out at 6 to 12 inches, C. carpatica is a well-behaved plant in moderate climates and conditions. C. rotundifolia, or American bellflower, is a taller cousin with graceful stalks bearing slender, elongated bell forms. Creeping Bellflower, C. rapunculoides, is infamous as an invasive weed. Resembling the American bellflower, this tough weed will take over a lawn given the right conditions.
Moist, well-drained soil is preferred for campanula plants. Thriving in rock gardens or as border plants, keep in mind that C. rapunculoides (creeping bellflower) will quickly spread to open areas if not maintained. This spreading variety is considered an invasive weed in many parts of the country, finding a home in meadows, near waterways and even in lawns.
Once an appropriate location is found, provide better drainage by incorporating organic compost, such as peat moss, to a depth of 12 inches. Space C. carpatica (Carpathian Harebell) plants 18 inches apart, and shorter species 10 to 12 inches to allow for air circulation and spread.
The campanula likes a little sun, but is a tender perennial that will need some special care in hot weather. Apply organic mulch, such as composted pine bark, at a level of about 2 inches deep around the plants. Avoid contact between the mulch and the crown of the plants to discourage disease. Keep the soil moist but not soggy, and be sure to provide adequate water during dry periods or for plants that receive lots of direct sun. Fertilize as you would your other perennials, with a slow-release granule or liquid fertilizer per manufacturer directions. Add additional mulch around the plants once they have died back in the fall for winter protection.
Both American bellflower and creeping bellflower may reseed more than desired in your perennial bed, border, or even your grassy lawn if not maintained. If you don't mind the plants remaining in your lawn but don't care for the flowers, mowing the stalks will remove the blooming foliage. To destroy plants completely, John Masengarb from the University of Minnesota Extension suggests digging down at least 6 inches and away from the plant to remove all roots. Herbicides such glyphosate may also be effective, but always follow the manufacturer's instructions carefully for safety and best results.