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How you make more campanulas depends on which kind you grow. Canterbury bells live only two years, so the only way to keep them going is seed. The perennials are multiplied from the plant itself, which keeps named varieties true to type.
Clump-forming perennials such as clustered, peach-leaved and milky bellflower are divided. The spreading kinds, spotted and Korean bellflowers with their running rhizomes and Serbian bellflower with its creeping stems, practically divide themselves, and rooted pieces can be lifted from the edge of a patch at almost any mild point in the growing season.
| Plant | Best method | Best timing |
|---|---|---|
| Canterbury bells | Seed | Collect in summer; sow late spring to early summer |
| Clustered and peach-leaved bellflower | Division | Early autumn, or early spring |
| Milky bellflower | Careful division or seed | Early spring or early autumn; resents disturbance |
| Spotted and Korean bellflowers | Rooted rhizome pieces | Spring or early autumn |
| Serbian and trailing bellflowers | Division or rooted pieces | Spring or early autumn |
Dividing perennial bellflowers
Divide when a clump has become congested, flowers less than it did, or has gone bare in the middle. Early autumn is the best time, when the soil is still warm and the divisions have several weeks to root before winter. Early spring, just as growth starts, is the second choice.
Milky bellflower and chimney bellflower have deep, fleshy roots and dislike being moved. Divide them only when needed, keep each piece large with a good length of root, and settle them in a spot where they can stay.
- Cut back and water Trim the top growth back to a few inches and water the clump the day before, so the root ball holds together.
- Lift the clump Dig around the plant with a fork, well out from the crown, and lift it with as much root as possible.
- Split into sections Pull or cut the clump into pieces, each with several healthy shoots and a good share of roots. Discard the old woody center.
- Replant straight away Set the divisions at the same depth in freshly prepared soil, 16 to 20 inches (40 to 50 cm) apart, and water in well.
- Keep an eye on them Water as the surface dries until new growth shows, then ease off. Shade them from harsh afternoon sun for the first couple of weeks.
Spreading kinds: lift and keep in check
Spotted and Korean bellflowers and their hybrids run by rhizomes, sometimes further than you would like. Each piece of rhizome with a shoot will make a new plant, so simply dig out rooted pieces from the edge of the patch and replant or pot them. Doing this every year or two also stops the patch from taking over the bed.
Serbian bellflower spreads the same way on a smaller scale. Pull away rooted sections from the edge of the mat, pot them in a gritty mix, and keep them in light shade until they take. It is also easy to tuck rooted bits into wall crevices or between paving stones.
Saving Canterbury bell seed
Leave a few of the best spikes to set seed after flowering. The capsules turn brown and papery through summer and open by small pores to let the seed out, so cut the stems as the capsules brown but before they have emptied. Hang them upside down in a paper bag in a dry, airy place to finish.
Shake out the fine seed, sieve off the chaff, and store it in a labeled envelope somewhere cool and dry. It keeps well for a couple of years. Canterbury bells cross freely, so saved seed gives a mix of colors rather than an exact copy of the parent, and double forms do not always come true.
Canterbury bells sometimes self-sow where the soil is open. Leave a few seedlings where they come up, or lift them young with a good ball of soil and move them where you want them.