University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article


Dr. Leonard Perry, Extension Professor
University of Vermont
Bellflowers (Campanula) are a popular and easily grown genus of perennials, wide ranging in flower shape (not just bell-shaped), flower color, bloom time, height, and growth habit.  They may be known as bluebells since this is the common color, although there are some selections in purple or lavender, pink and white. "Harebells" generally refers to one species (rotundifolia) found growing in meadows and hillsides of Scotland and England. There are about 300 annual, biennial, but mainly perennial species native to various habitats of temperate regions in the Northern Hemisphere.
Most bellflowers grow best in full sun, yet there are several species that grow well in part shade (lactiflora, latifolia, takesimana).  Most are hardy throughout the north, except a couple popular species only listed as hardy to USDA zone 5 (-10 to -20 degrees F in winter).  Included in the least hardy are the milky bellflower (lactiflora) and delphinium bellflower (latiloba).
They need well-drained soil, soggy soils causing root rots and loss over winter.  Some species, however, prefer moist soils (lactiflora, latifolia, takesimana).  Generally bellflowers don't require much fertility, too fertile soils causing too vigorous aggressive growth in some spreading species (glomerata, punctata, rapunculoides). 
In addition to a range of flower colors, bellflowers may have upright or nodding flowers, single or in clusters.  In addition to bell-shaped or "campanulate", flowers may be cup-, bowl-, tubular-, or star-shaped.  Generally plants have differing basal and stem leaves on the flower stalks, the basal ones usually larger and with cut margins. 
Between 1998 and 2006, Richard Hawke of the Chicago Botanic Garden (USDA hardiness zone 5b) evaluated 89 different bellflowers, the results providing much useful information on these plants for northern gardeners.  Plants were rated on such traits as flower production, habit, and winter hardiness.
Generally the cultivars (cultivated varieties) of a species performed similarly, and similar to the species.  Several popular species and their cultivars performed poorly including the milky bellflower (lactiflora), the great bellflower (latifolia), the delphinium bellflower (latiloba), and the peachleaf bellflower (persicifolia).  Poor quality and losses of these may be due in part to the water-retentive heavy soils of the trial site.
Another genus performing poorly, either from winter losses or poor flowering, were the Carpathian bellflowers (carpatica) including the popular 'Blue Clips' and 'White Clips'.  A good substitute for these would be 'Samantha', with similar bowl-shaped flowers only a darker purple blue.  This cultivar grows about 12 inches high and 20 inches wide, and bloomed in Chicago from early June to late August.
The bellflower that stood out as best of all in this study was 'Sarastro' with its compact habit about two feet high and wide, its many violet blue tubular flowers from early June to late July, and winter hardiness.  This is a cross between the spotted and nettle-leaved bellflowers, but doesn't spread.  Another cultivar scoring highly in the Chicago trials was 'Purple Sensation' with its deep purple bell-shaped flowers through the summer, and mounded habit similar to 'Sarastro'.

Species and their cultivars that rated highly included the clustered bellflower (glomerata), Serbian bellflower (poscharskyana), spotted bellflower (punctata), rampion bellflower (rapunculoides), bluebell (rotundifolia), and Korean bellflower (takesimana).  Keep in mind the spotted, rampion and Korean bellflowers may exhibit wide-spreading and vigorous growth, overrunning weaker adjacent plants.  A popular hybrid of the Korean and great bellflower, 'Kent Belle' is upright and non-spreading with violet blue, bell-shaped flowers from mid June to mid August.  About 40 inches tall and 30 inches wide, it tends to be floppy and need staking.
Of the nettle-leaved bellflower tested (trachelium), the cultivar 'Bernice' is recommended as being free of foliar chlorosis.  Reaching about a foot and one half high and wide, it has cup-shaped double flowers, violet blue, from mid June to late July. 
Of the several Dalmatian bellflowers (portenschlagiana), 'Resholdt's Variety' rated highly with no winter losses as its relatives experienced.  Its bell-shaped, violet blue flowers are early, from early May to early July in Chicago, on plants only 4 inches high and 18 inches wide. A hybrid of this species and the Serbian bellflower, the popular 'Birch Hybrid' had upward-facing, bell-shaped violet blue flowers on compact plants, yet losses in several winters.
From these Chicago trials, it appears the best lower choices, but not vigorously spreading, would be 'Samantha', the Serbian bellflowers, and 'Resholdt's Variety of the Dalmation bellflower.  The best taller choices (two feet or more) to consider are 'Purple Sensation', 'Sarastro', rampion bellflower, and some cultivars of the clustered bellflower. 
The complete results of these trials, as well as those with other perennial genera, can be found online under the research section at the Chicago Botanic Garden (

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