Gadenin日本語Get the appWhich campanulas you actually sow
Campanula is a big genus, and the bellflowers in gardens fall into two camps. Canterbury bells (Campanula medium) are biennials: raised from seed one year, they make a leafy rosette, sit through winter, and throw up their tall spikes of fat bells the following year before setting seed and dying. They are the campanula almost everyone sows.
The perennial bellflowers, from clustered and milky bellflower to the Serbian ground-cover kind, are usually bought as potted plants and kept for years. Some can be raised from seed, but named forms do not come true and plants take a season or two to reach flowering size, so dividing or buying a plant is the easier route. This guide focuses on Canterbury bells; see the propagation guide for multiplying the perennials.
| Type | How it is usually started | First flowers |
|---|---|---|
| Canterbury bells, standard biennial strains | Seed in late spring to early summer | The following late spring and early summer |
| Canterbury bells, early F1 strains | Seed in early autumn, then a cold winter | The next spring, a little shorter |
| Perennial bellflowers | Bought plants or divisions | The first full season after planting |
When to sow Canterbury bells
The classic timing is late spring to early summer. That gives the plants the whole summer and early autumn to build a strong rosette, which is what carries a big flower spike the following year. Sow much later and the rosettes go into winter small, flower weakly, or skip a year.
A plant has to feel a spell of winter cold before it will flower, whatever the strain. Some F1 Canterbury bell strains are bred to flower from an autumn sowing, which is handy if you missed the summer window, but they still need that cold period and will make shorter plants. There is no strain that flowers from a spring sowing in the same year without it.
Germination and pricking out
The seed is tiny and germinates best at around 68°F (20°C), usually within one to two weeks. Press it onto the surface of a fine seed mix and cover it barely, if at all. Keep the tray evenly moist and out of hot direct sun; early summer sowings can dry out in an afternoon.
Canterbury bells dislike root disturbance, so do not leave the seedlings crowded in the tray for long. Move them on while they are still small, at the first true leaf or two, into plug trays or pots about 2.5 inches (6 cm) across. Handle them by a leaf, never the stem, and lift each with as much of its root intact as you can.
- Sow on the surface Fill a tray with fine, moist seed mix, scatter the seed thinly, and press it in lightly. A dusting of vermiculite is plenty of cover.
- Keep it near 68°F (20°C) Stand the tray in bright shade and keep the surface moist, watering from below so the seed is not washed about.
- Prick out early At the first true leaves, move each seedling into its own plug or 2.5 in (6 cm) pot, disturbing the root as little as possible.
- Grow on in small pots Pot on once roots fill the plug, keeping the root ball whole each time, until the plants are ready to go out in early autumn.
Getting young plants through the summer
Summer is the hard part. Young Canterbury bells sulk and rot in hot, humid, still weather. Keep the pots in part shade, somewhere with a breeze, and water only when the mix starts to dry; soggy pots in hot weather are how most seedlings are lost. A slightly dry, airy spot beats a lush sheltered one.
Give a weak liquid feed every couple of weeks once the plants are growing well, but do not push them with strong fertilizer. The aim is a compact, sturdy rosette with plenty of roots by the time the heat breaks.
If your summers are very hot and muggy, an autumn sowing of an early-flowering F1 strain is often less trouble than nursing seedlings through the heat.
Planting out in early autumn
Plant out early in autumn, while the soil is still warm, so the roots can spread before the cold arrives. A well-rooted rosette shrugs off winter; one planted late sits loose in cold wet soil and often rots. Space plants 8 to 10 inches (20 to 25 cm) apart in a sunny or lightly shaded bed.
Canterbury bells prefer neutral to slightly alkaline soil. About two weeks before planting, work in dolomite lime at roughly 3 ounces per square yard (about 100 g per m²) along with compost or leaf mold, then firm the plants in and water them well.