Captivating campanulas for the rock garden

Introduction

Campanulas, or bellflowers as they are universally known, are among the favourite plants of most alpine gardeners. Many flower later in the season than most alpines, thus extending interest from spring into summer. There is plenty of choice for those wishing to explore the genus as it includes over 500 species and many subspecies. These are distributed across the temperate and subtropical regions of the Northern Hemisphere, with centers of diversity in the Mediterranean region, Balkans, Caucasus and mountains of Western Asia. The range also extends into mountains in tropical regions of Asia and Africa, but these species fall outside our sphere of interest. They vary in habit from dwarf arctic and alpine species under 5 cm high, to large temperate grassland and woodland species growing to 2 metres tall. Let’s take a look now at some of the campanulas suitable for the rock garden.

Cultivation

Some of the more vigorous, lower growing campanulas are excellent plants for the larger rock garden. These are among the easiest alpines to grow and propagate. But it is not of these that I write, but some of the smaller, some would say more choice kinds. They are ideal for growing in sunny troughs, crevice beds, and choice corners in the rock garden. While most alpine campanulas tolerate shade they flower much more freely in full sun. In general they are drought tolerant.

Almost all bellflowers, including those mentioned here, tolerate or even revel in limy soil. What they will not tolerate is poor drainage. Be sure to prepare their site so as to exclude this possibility. Dwarf campanulas mostly have fibrous root systems rather than a taproot, and do not root very deeply. What these types do appreciate is a coarse gravel mulch through which they may ‘run’ freely, forming gradually spreading clumps.

Pot-grown campanulas may be planted at any time of the year. Water well until they are established after which you will rarely need to water them at all.

Propagation

Seed

Campanulas are easily propagated from seed, which is generally produced in abundance. However, the seed is dust fine so is easily lost. You need to watch the capsules when they are beginning to change from green to brown. When this happens collect them before the tiny slits through which the seeds are released open. Place them in an envelope or similar in a dry, sunny place until this occurs.

The seed may be sown at any time. I have found the best method is to use the so-called ‘suck-down’ principle, which I use for most very fine seed. Add a thin layer of 2-5mm (one-eighth to one-quarter inch) sharp gravel to a potful of whatever seed compost you normally use. Sow the seed very thinly on the surface of the gravel. Then place the pots in a tray of water sufficiently deep for capillary action to wet the compost and surface chippings through. Take the pots out and allow them to drain. The excess water, and with it the seeds will be gently sucked down into the interstices in the gravel. There they will have adequate water and air for good germination. I place the pots in a covered and lightly shaded cold frame until germination occurs.

In most cases the seedlings are unlikely to be big enough to handle individually. If so, I prick them out in groups and separate them later when it is easier to do so.

Vegetative propagation

Most campanulas can be increased by simple division, lifting a clump and teasing the fibrous roots apart. You can either replant the divisions directly into a prepared site, or pot them up and grow them on. In either case make sure to keep them well watered until established.

For those, mostly the trickier species, for which simple division maybe unsuitable, soft cuttings are a possibility. Take small pieces of rapidly growing material, preferably without flower buds. Trim off the lower leaves and root them in pure sharp sand in a propagator. Make sure to keep them shaded and watered. Pot them up when they are making vigorous new growth. Don’t be surprised if success rates are low. The cutting material tends to be very soft and easily succumbs to attacks by fungal and bacterial diseases.

A selection of easy campanulas for the rock garden

There are so many dwarf bellflowers suitable for the alpine garden that it is difficult to choose a few. Those described here are all available in the nursery trade, can be grown outside in the UK without protection, and none will prove troublesome, as some of the larger more ebullient growers might. All of the photograhs were taken in our garden in North Wales, a notoriously damp and windy location!

Campanula arvatica

This little gem’s natural home is among limestone boulders in the mountains of northern Spain. In both its typical dark violet form and a glistening white selection it is an easy plant to please in any very freely drained, sunny rock garden site. A limestone scree provides particularly favourable conditions. It is a gentle spreader, rooting as it goes, but is easily pulled out and never becomes a nuisance. Propagation by division as described earlier is simplicity itself.

Campanula pusilla  ‘Cambridge Blue’ & ‘Elizabeth Oliver’

This delightful little bellflower is often still labelled with its old name (Campanula cochlearifolia). Like C. arvatica it is a gentle runner through any friable surface, and is equally easily propagated by division. You may encounter the species almost anywhere in the mountains of southern Europe from Spain to the Carpathians. Indeed, you may find it without really looking for it as it often encroaches onto the gravelly verges of mountain roads.

It is a very variable species as far as flower colour is concerned, ranging from deep violet through various paler shades to the exquisite china blue of  C. pusilla ‘Cambridge Blue’. An equally good albino is also available. I am including too the unusual and lovely little double, Campanula pusilla ‘Elizabeth Oliver’.

Campanula x wockii ‘Puck’

This little beauty flowers in August here in North Wales, and continues into early September. It’s parentage is uncertain but is believed to be Campanula pulla x Campanula waldsteiniana, both beautiful dwarf species in their own right. Unlike those I have described so far it is not a spreader but a very slow clump former, the plant illustrated is 12 years old. Once the plant has finished flowering I give it a haircut with a pair of scissors to tidy it up before winter. It is a perfect plant for even a small trough as it will never outgrow its allotted space. I propagate it by exposing the roots around the clump and prising out rooted pieces, and have not tried it from cuttings.

Campanula raineri

The upturned, large, sky-blue flowers of this queen among campanulas sparkle in the summer sunshine. No less breathtaking are the slightly more cup-shaped blooms of the albino.

Neither is particularly easy to grow, but not by any means impossible. A sunny position in very well drained soil in a trough is the ideal location. But it can be cultivated very successfully under glass either planted out or in a pot. It spreads gently underground and as with other campanulas described earlier, these rooted pieces are the best means of increase. If more than a few plants are required, seed is an alternative.

There are various excellent hybrids with C. raineri as one parent, the best in my experience being those with Campanula morettiana. The very old C. ‘Joe Elliott’ is my favourite.

If you’ve enjoyed this page on captivating campanulas for the rock garden, why not take a look at some of our other articles on alpine plants?

Author: John Good