Campanulas are without doubt one of the most charming of cottage garden plants. The taller species typically grown in gardens provide heads of loose open bell-like flowers in blue, white, purple and sometimes pink. Some however have a low creeping habit and are very at home around the edge of a patio or tumbling over stones in a rockery.
There are over 500 species in the genera Campanula¹ and so it is going to be difficult to do the genus justice. I will concentrate here on those that we grow in the gardens at Waverley or have used as cut flowers over the years (C. medium, C. persicifolia, C. latifolia, C. glomerata, C. pyramidalis and C. portenschlagiana).
Campanulas mainly come from the temperate and sub-tropical regions of the northern hemisphere. Many are native to Europe originating in the Mediterranean and eastwards to the Caucasus mountains. Understanding where these plants come from and the conditions they enjoy in the wild, is critical to providing them with the conditions in which they will thrive in your own garden.
Some species of Campanula are annuals, whilst others are biennials or perennials. Although species like C. medium may be perennial in some areas we tend to grow them as biennials so that we get fresh vigorous flowering plants each year.
Sowing from seed is very straight forward. The seeds are very small and typically we would sow thinly onto the surface of moist compost in the spring and then cover the tray with cling film until the seeds germinate. I usually remove the cling film as soon as the green shoots emerge to avoid any danger of damping off. Try to avoid watering from the top as the seeds will easily be washed into the corner of your tray.
Once the seedlings have their first true leaves they can be pricked out into larger trays or modules and grown on. They seem to transplant very successfully. As we grow species like C. medium as biennials we prick them out into large modules where they stay until mid-September. At this point the established plants are very easy to set out in groups around the garden where they over winter and flower in early summer.
The hardy perennial species eg. C. persicifolia are perhaps easier to propagate by division every few years. I simply dig up a clump, separate out the new rosettes and pot them up into individual 9cm pots filled with a mix of perlite and multi-purpose compost.
All of our Campanulas do well throughout the garden when planted in full sun or partial shade. As tall plants C. medium look very effective peeking out behind our low formal Lonicera nitida hedges and in front of the more informal woodland edge of the garden boundary . Many writers recommend that they prefer a moist but well drained soil.
Pest and diseases
I have to say that we find all our Campanulas to be pretty resilient to pest and diseases. It is reported that they are susceptible to slugs and snails but we have very little problem (perhaps they are attracted away by other more tasty morsels!).
It is also reported that they are prone to powdery mildew and rust diseases but again we have had little problem with these diseases on our plants. In order to see the flowers at their best we do space the plants well apart and this may well allow plenty of air to circulate between them thus keeping these diseases at bay.
Armitage and Laushman² report that Campanulas do not seem to need a period of cold treatment to start producing rosette leaves but do need a period of cold to initiate flowering. C. persicifolia, for example, requires 12 weeks at or below 4°C to initiate flowering. Treating sown plants as biennials seems to sit well with these findings. Our spring sown plants of C. medium do not seem to flower in the year that they are sow. However, planted out in mid-September and allowed to over winter in the cold flower beds they produce robust, upright, tall plants that flower over a long period.
Armitage and Laushman also indicate that C. persicifolia is day neutral which means it flowers under both short or long days once the cold treatment requirements have been satisfied. For other Campanula species long days are required for flowering after vernalisation. (see: How plants use day length to decide when to flower (Photoperiodism) for more background on this).
It would appear that the new Champion series of Campanula medium does not require cold treatment which means they can be grown more effectively in greenhouse conditions. This helps enormously if you are growing purely to produce cut flowers and want a longer season of production.
Cutting and conditioning
It is certainly our experience that the tall varieties of Campanula all make excellent cut flowers. The inflorescence opens from the bottom providing a long period of interest in the vase and in the garden.
Typically you would cut when the bottom one or two flowers have coloured and are open. We use a standard conditioning approach of cutting the flowers directly into cool, clean water containing ‘flower food’ to keep the water fresh and minimise bacterial development.
The stems often produce sap when cut so it is wise to keep them in a separate bucket from other flowers, rinsing the cut stems every 20 minutes or so until the sap stops flowing.
C. medium, C. persicifolia, C. latifolia and C. pyramidalis all offer a light, airy and open effect which is ideal for natural, country style arrangements and bouquets. C. glomerata is perhaps more structural, upright and dense in form but its strong purple shade works well with bold colours like oranges and scarlets.
Whereas many of the Campanulas we grow are upright and need some support to produce quality blooms we have seen beautiful trailing forms on our travels in Croatia and Montenegro this year growing in very dry, well drained, rocky conditions on walls and buildings. It is often very difficult to get good trailing colour for use in flower arrangements and this growing approach is well worth considering.
Campanula medium (Canterbury Bells)
Originating from southern Europe¹ these large robust plants grow to 2 feet to 2 feet 6 inches in height. They have a long flowering season starting in June and continue through to August. As the flowers open consecutively from the bottom to the top they provide a long period of interest and colour. They are quite heavy plants and although they have robust stems they do tend to need some support to stop them looking untidy.
We grown these from seed each year and treat them as biennials. The RHS considers them to have a hardiness rating of H4 (Hardy through most of the UK (-10 to -5)).
We have grown two forms: the cup and saucer varieties which have big robust flowers on strong stems and also the singles (which do not have the saucers). We do find these rather ‘chunky’ in nature and are not really delicate enough for use in bouquets and small arrangements.
The ‘Champion’ series, however, that you typically get from your floristry wholesaler are a very different cut flower and we have used these extensively over the years. Grown as an annual they can be brought through to flowering in around 15 weeks. They are available in a range of colours from blue through white and to pink.
Campanula persicifolia (the peach leaved campanula)
To my mind C. persicifolia is rather more attractive and delicate than C. medium. This species is a perennial that is native to most of Europe and the Benelux countries eastwards towards Central and Southern Russia and North West Turkey³. It seeds itself freely around our garden but is also easy to multiply by division (the latter technique particularly useful if you want to bulk up the delicate ‘alba’ form).
C. persicifolia has evergreen foliage and has been given the H7 hardiness rating by the RHS (Hardy in the severest European continental climates (< -20)). In nature it grows in meadows, open woods and on the edge of forests.
As with C. medium the inflorescence opens from the bottom to the top. This give a long period of flowering in the garden border. Flowering can be extended still further by dead heading. In this case you are not removing the whole flower spike but removing the individual dead flowers before they set seed. You will find new flowers develop at the base of each flower stem.
Campanula pyramidalis (the Chimney Bell Flower)
When grown well C. pyramidalis can grow up to 2 metres in height producing tall spikes of pyramid shapes flowers that are excellent for large flower arrangements. Flowering from May until July, it is a short-lived perennial that, like C. medium, is often grown as a biennial. It is native to southern Europe and the western Balkans¹.
Campanula glomerata (the clustered bellflower)
C. glomerata is a vigorous rhizomatous perennial that has a tendency to sucker. The species is native to the North Temperate Zone of Eurasia, from Europe to Japan¹. It grows to around 1-2 feet in height producing clusters of typically deep purple flowers on strong stems. There is also a beautiful crisp white variety (see below). The RHS website indicates that it is hardy in the severest European continental climates (< -20) (RHS hardiness rating H7).
Campanula latifolia (the giant bellflower)
Very much more delicate than C. glomerata or C. medium, C. latifolia is one of my favourite Campanulas in the garden. It seeds freely and seems to come back without problems year after year in a rather inhospitable spot in the garden. We tried to move some seedlings to what we considered to be rather better soil and they just did not ‘do’. The answer I think is that that actually like poor dry soil.
C. latifolia is again native to Europe extending to western Asia as far east as Kashmir.
Campanula portenschlagiana (the wall bellflower)
Very different in form from the others mentioned in this article is C. portenschlagiana. This is a very robust, low growing creeping plant that in our garden grows in minimal soil around the base of the house and patio steps. It was at the house well before we arrived 25 years ago and I am sure will still be about when we finally leave. It produces masses of blue flowers throughout the summer.
It is an alpine plant and requires a very well drained area in full sun to thrive. We have found that is does not compete well with plants like Saxifraga x urbium (London Pride) which can easily swap this Campanula if not kept in check.
And finally some trivia …
Su Whale⁴ in her guide on cut flowers cites the following charming piece of flower trivia. In Germany and in the Netherlands the Campanula flower is known as ‘Rapunzal Bellflower’ and supposedly was the inspiration behind Grimm’s fairy tale.
² “Specialty Cut Flowers – the production of annuals, perennials, bulbs and woody plants for fresh and dried cut flowers” by Armitage and Laushman (ISBN 0-88192-579-9)
³ “Perennial – Volume 2” by Roger Phillips and Martyn Rix (ISBN 0-330-29275-7)
⁴ “Cut flowers – a practical guide to their selection and care” by Su Whale (ISBN 978-0-9568713-0-5)