University of Vermont Extension
Department of Plant and Soil Science
Summer News
Article
BELLFLOWERS
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
(www.chicago-botanic.org/research/plant_evaluation/#notes).
Return to
Perry's Perennial
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