(Editor's Note: This article was originally published on February 8, 2008.)
One of the most popular genus of alpines plants for utilizing in rock garden setting are Campanula, commonly known as the bellflowers. There are well over 300 species, all found north of the equator. The vast majority of species hail from the Mediterranean and Middle East, but a few are native to North America, many in east Asia and some even extend into the Arctic. With so many species, it is not surprising that there is great variation among the species. Some are tiny creepers rarely exceeding a few centimetres while others are giants reaching 2 m or more. However, all have flowers that are more-or-less based on a bell-like theme. The blooms may be nodding or upright, narrow or wide. They may be arranged in clusters, solitary or spikes. Blue is by far the most common colour, but depending on the species, may be white, purple, pink or even yellow.
Many bellflowers are challenging to grow outside their native ranges. Gardeners in drier, milder areas can grow a wider variety than those of us who live in the coastal Pacific Northwest, eastern USA and Canada. And since many gardeners have space constraints, this article will deal with those smaller species that are quite tolerant to cold, wet winters.
Culturally, these winter-wet bellflowers do not present any growing challenges. Provide them with well-drained, slightly acidic to slightly alkaline soil and at least half a day of sun and most will thrive. Most of the species about to be described are hardy to at least USDA zone 4, some even hardier. Most bloom in early summer.
Availability varies but most should be available at either local nurseries, mail-order alpine specialists or seed exchanges. I have grown most of mine from seed. Seeds need stratification so sow them in the fall and overwinter in a cold frame or place pots in a cool garage or fridge for 6-8 weeks to simulate a winter.
The most widespread Campanula is C. rotundifolia, the common harebell. This species grows in both Europe and North America, extending to the Arctic Circle. It is a very hardy species and easy to grow. The flowers are held on thin, wiry stems between 20-40 cm. Plants will creep about and may self-seed so prompt dead-heading is recommended. Plants produce medium blue, nodding bells in loose spikes but flowers may range from deep blue to pale ice-blue and white.
Above: C. rotundifolia and the alba form
Carpathian harebell, C. carpatica, is probably the most popular. Plants are very hardy and form mounds that cover themselves in relatively large upright bells in shades of blue along with white. Plants vary in size from 15-30 cm and are available in a number of named cultivars such as ‘Blue Clips’, ‘White Clips’, ‘Blue Gem’, and ‘White Gem’. This one also has self-seeding potential, so head-heading is highly recommended.
Above: C. carpatica and a white form
Serbian bellflower, C. poscharskyana, is one of the best bangs for the buck. In my garden, this one blooms for nearly 2 months. Plants are somewhat sprawling and plants spread by underground rhizomes. The flowers are somewhat star-shaped and produced in loose spikes along 30 cm stems. Like C. carpatica, this species also has a number of named cultivars. The standard species is mid-blue but ‘E. H. Frost’ has ice-blue flowers while ‘Lilacina’ has lavender-pink and ‘Glandore’ has violet-blue. ‘Blue Gown’ is a dwarf blue version.
Above: C. poscharskyana, 'Lilacina', 'E. H. Frost' and 'Blue Gown'
Somewhat similar is the Dalmatian bellflower, C. portenschlagiana. This species has upright bells and also spreads by thin rhizomes but is not invasive. The plants are more compact than C. poscharskyana, with somewhat trailing stems to 25 cm. They also have a rather long blooming season. The cultivar ‘Birch Hybrid’ is a lovely combination of both the Dalmatian and Serbian bellflower.
Above: C. portenschlagiana and 'Birch Hybrid'
A neat and tidy species is the Adriatic bellflower, C. garganica. This one forms cushions to about 12 cm with loose clusters of upright star-like flowers on thin stems. The flowers are mid-blue. Perhaps the best known cultivar os ‘Dickson’s Gold’ whose bright yellow foliage contrasts beautifully with the dark violet-blue flowers. ‘Hirsuta’ has fuzzy, grey-green foliage.
Above: C. garganica and 'Dickson's Gold'
One of the most dainty species is the fairy thimble bellflower, C. cochlearifolia. Unfortunately, it is one of the most invasive! However, growing between cracks in walls and between stepping stones, will help keep them under control. This species produces several somewhat nodding bells on wiry 10 cm stems. This one is available in various shades or blue as well as white. ‘Elizabeth Oliver’ is a later-flowering double form which is particularly attractive.
Above: C. cochlearifolia, C. cochlearifolia 'Alba' and C. cochlearifolia 'Elizabeth Oliver'
Another dainty species is C. pulla. This one runs but ever so gently. The flowers are mostly solitary, nodding and deep violet-blue, produced on wiry 10 cm stems. Yet another runner is C. chamissonis (aka C. pilosa, C. dasyantha). This one essentially forms a mat of shiny green foliage studded with nearly stemless, upward-facing blue and white bicoloured bells.
Above: C. pulla and C. chamissonis
For something a little different there is C. betulifolia, the birch-leaved bellflower. This one produces trailing stems to 30 cm that arise from a thick taproot. The flowers are produced in loose clusters and are cream-white, often with a slight pink flush. Other attractive tap-rooted species include C. aucheri, C. tridentata and C. saxifraga. These are lime-lovers that form mounds to about 15 and many solitary, relatively large violet-blue upright bells. Sitting on the fence in regards to size are C. kemulariae and C. raddeana. Both form slowly spreading mounds to about 30 cm. I grow them both in the rockery as well as the front of the border. They both have somewhat upright branched stems and loose clusters of nodding, relatively large violet-blue bells. Both of these are lime-lovers.
Above: C. betulifolia, C. saxifraga and C. raddeana
The last of the easy dwarf alpine bellflowers I can suggest is the bearded bellflower, C. barbata and C. patula. The former species is perhaps best grown as a biennial and allowed to self-seed after blooming to maintain plants for future blooms. In the first year, plants produce a flat rosette while in the second, they produce a single upright stem to 30 cm with a terminal, loose cluster of nodding blue to white bells that are conspicuously hairy along the fringes of the blossoms. This species prefers acidic soil. Campanula patula is definitely a biennial and should also be allowed to self-seed. This species produces several upright branching stems to 30 cm with numerous , somewhat nodding star-like bells of a lovely rose-purple. A drift of plants has been described as’ a tossing seas of hot lilac-lavender’. They have a very-long blooming season. They are particularly nice planted among yellow-flowering alpines.
Above: C. barbata and C. patula among Eriophyllum lanatum
These are but a few of the lovely alpine bellflowers that exist. They are among the most care-free and hardy and reward the gardener with blooms throughout June-July.