Few groups of flowering plants show the diversity of the bellflower clan, or campanulas. With bell-shaped, tubular or star-shaped flowers in shades of blue, white, pink, and red, they have growth habits that range from low and creeping to tall and upright. Most of the garden-worthy choices are perennials, although there are some annuals and a biennial in the genus. And all are beautiful, even the few that are such vigorous spreaders and seeders that you may need to think twice about including them in your garden.
To help gardeners choose from among the many possibilities this genus offers, the Chicago Botanic Garden evaluated 89 different species and cultivars for eight years in their Zone 5 gardens. Plants were grown in full sun and given only minimal maintenance in an effort to duplicate the kind of care they would receive in most home gardens. Plants were evaluated for ornamental quality, vigor, resistance to pests and disease problems, and winter hardiness, receiving an overall rating of from one to five stars.
The sole five-star winner was the 22 inch tall hybrid cultivar 'Sarastro'. A cross between Campanula punctata and C. trachelium, 'Sarastro' has a compact, non-spreading habit and a profusion of large, tubular, violet-blue flowers over a long period.
Many other plants received a four-star rating, including the low-growing, spreading Serbian bellflower (C. poscharskyana) and several of its cultivars, and the petite, long-blooming hybrid 'Samantha'. Given the range of sizes, colors, and growth habits, there is no doubt a bellflower that is just right for a spot in your garden.
To read the entire bellflower performance appraisal, go to: Chicago Botanic Garden.