How to Grow Canterbury Bells
'Crown Single Mixed' from Seed
The biennial that fills the June Gap — towering 80–100cm spires of nodding bell-shaped flowers in blue, pink and white that bloom precisely when spring tulips have finished and summer annuals haven't yet peaked, a cottage garden classic since the sixteenth century that bumblebees use as an overnight shelter inside the bells
Canterbury Bells have been grown in English cottage gardens since the sixteenth century — named for their resemblance to the bells of Canterbury Cathedral, they became one of the defining plants of the Victorian flower garden and have never fallen entirely out of fashion, because no other plant occupies quite the same space in the early summer border. The large, nodding, broadly bell-shaped flowers in soft blue, pink and white appear in June and July — exactly the period known as the June Gap, when the last of the spring tulips have finished and summer-sown annuals have not yet reached their peak. In that transition window, the statuesque 80–100cm spires of Canterbury Bells provide height, structure and a romantic, heritage quality that few other plants can match.
They are biennials — a growth pattern that requires understanding and planning but rewards with a performance that annuals cannot replicate. In year one, the seedling forms a leafy, low rosette of dark green leaves that overwinters in the garden. In year two, it transforms: the stem shoots upward from April onwards, reaching 80–100cm by June and producing the magnificent bell-laden spikes that are the whole point of the plant. The wait is not long by gardening standards — six weeks of patience from sowing to autumn establishment, a winter of quiet root development, and then a spectacular June display of the kind that makes anyone who sees it want to know the name of the plant and where to get seed.
Quick Facts at a Glance
Plant Type
Hardy Biennial (H5 — two-year cycle)
Sow in Year 1
April–June (for flowers next summer)
Flowering in Year 2
June – July
Height
80–100cm — staking recommended
Position
Sun or partial shade; fertile, well-drained
Difficulty Rating
2 out of 5 — Easy (patience required)
Understanding the Biennial Cycle
Campanula medium is a true biennial — a plant that takes exactly two years to complete its life cycle. In year one, it germinates, forms a leafy rosette, and overwinters in the garden as a sturdy, compact plant. The cold of winter is not merely tolerated but required — it triggers the hormonal changes (vernalisation) that allow the plant to bolt upward and flower in year two. Without overwintering, Canterbury Bells will not flower. This is why the sowing window — April to June of year one — is critical: too late in the year and the plants don't establish sufficiently to overwinter and flower the following summer.
The June Gap — Why This Plant Matters Strategically
The June Gap is one of the most discussed challenges in British garden design — the two to four weeks in early June when spring-flowering bulbs and biennials have finished and the main flush of summer perennials and annuals has not yet reached its peak. Canterbury Bells are one of a small group of plants bred to flower precisely in this window, providing height and drama when the border most needs it. Combined with Foxgloves, Alliums and the last of the late tulips, they create the bridge between spring and summer that separates a continuously beautiful garden from one that has bare patches in June.
🐝 Bumblebees Sleep Inside the Bells
Canterbury Bells provide one of the most charming and least-known pollinator services of any garden plant: bumblebees — particularly male bumblebees and emerging queens — use the large, pendulous bell-shaped flowers as overnight shelters. On cool summer evenings, bees crawl inside the bells to shelter from dew and low temperatures, and remain there overnight, emerging in the morning warmth. Look into an open Canterbury Bell flower on a cool summer morning and you may find a sleeping bumblebee using the bloom as a natural hotel. This is a known and well-documented behaviour that gives the bells a dual role — daytime nectar source, overnight shelter — that no other commonly-grown garden flower provides.
Sowing & Establishment
Surface Sow — Light Required for Germination
Canterbury Bell seeds are tiny and require light to trigger germination — surface sow onto moist compost, pressing gently into contact, but do not cover. A thin dusting of fine vermiculite (1mm maximum) is acceptable; the seed should still be visible. At 15–20°C germination takes 14–21 days. Do not attempt to speed germination by burying seed — this is the most common cause of germination failure.
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Sow indoors April to June, or into a nursery bed outdoors May–June. Surface sow onto moist seed compost or fine garden soil. Press gently; do not cover. Keep at 15–20°C. Germination takes 14–21 days. In modules, sow two seeds per cell and thin to the strongest.
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Grow on in a nursery bed or large pot through summer. Prick out into a dedicated nursery patch — a small area of prepared ground — when seedlings have their first true leaves. Space 10–15cm apart in the nursery bed. Feed every two weeks with a balanced liquid fertiliser to build strong rosettes before winter.
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Transplant to final positions in September–October. When the rosettes are well-established — typically eight to twelve weeks after sowing — transplant to their final flowering positions. Space 30cm apart in fertile, well-drained soil. Plant at the same depth as the nursery bed. Water in well. The plants will remain as low rosettes through winter, showing little visible activity but developing their root systems.
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Stake as the spikes develop in spring. From April, the central spike begins to rise. Insert bamboo canes or support rings when stems reach 30cm — before the heavy bell clusters develop. At 80–100cm with substantial flower load, unsupported spikes blow over in summer wind and rain.
Growing On & Care
Harvest for the Vase
Canterbury Bells are exceptional cut flowers with a vase life of seven to ten days — among the longest of any cottage garden flower. Cut stems when the bottom two to three bells are fully open but the upper buds remain closed. As the bottom bells fade, the upper buds open progressively, extending the display in the vase over several days. Condition in deep, cool water for several hours before arranging.
Moisture Through Summer
Canterbury Bells need consistently moist soil through their flowering period in June and July — drought causes flowers to develop quickly and fade faster, shortening the display. Water deeply at the base in dry spells. Mulch around the base of plants to retain moisture and keep roots cool during warm summers.
After Flowering
Once the main spike has finished, cut it back to encourage side shoots, which may produce a few additional bells over the following weeks. Remove plants entirely by August — they are monocarps (flowering only once then dying), and leaving dead stems is untidy and a disease risk. Sow fresh seed in June to maintain continuity for next year.
Plan Two Years Ahead
The key to continuous Canterbury Bell display is to sow every year in May–June, establishing plants that will flower the following summer. A two-year rolling sowing plan — established plants flowering this June, new seedlings going into the nursery bed this June — produces flowers every year without fail. Gardeners who sow once and wait miss the continuity that makes biennials so rewarding when properly planned.
Colour in the Mix
The 'Crown Single Mixed' provides blue, pink and white in one packet — the blue is particularly fine, a clear periwinkle-blue that is harder to find in modern border plants than most gardeners realise. In a mixed planting, the blue makes the pink appear warmer and the white appear cooler simultaneously — a colour dynamic that the single-colour selections available from some suppliers cannot replicate.
Heritage Partners
Canterbury Bells have been grown alongside Foxgloves in cottage gardens for centuries — both are heritage biennials that flower simultaneously in June, both reach 80–100cm, and the combination of the Canterbury Bell's horizontal, nodding bells with the Foxglove's upright, tubular spires creates a layering of form that is one of the great visual achievements of the traditional British cottage garden. Sow both in the same nursery bed in May–June.
The Two-Year Calendar — Planning Your Display
Because Canterbury Bells flower in year two, the calendar looks different from an annual's — the sowing year and the flowering year are always different. Here is what a continuous rolling display looks like across two years.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| 🌱 Sow (Yr 1) |
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| 🍃 Overwinter |
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| 🔔 Flower (Yr 2) |
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Common Problems & Solutions
| Problem | Likely Cause | What to Do |
|---|---|---|
| No germination | Seed covered; temperature too low or too high | Surface sow — do not cover. Germination requires light. Maintain 15–20°C. Below 12°C germination is slow; above 25°C it may fail entirely. A cool indoor windowsill in May or June is ideal. |
| Plants don't flower in year 2 | Sown too late; didn't overwinter; insufficient vernalisation | Sow no later than June of year 1. Plants must establish as decent-sized rosettes before winter — at least 10–15cm across — to have sufficient energy to flower the following summer. Very small, late-sown plants may skip the flowering year. Sow again the following April–June. |
| Spikes fall over | Insufficient staking; wind and rain | Stake when stems reach 30cm in spring — before bell clusters develop. Use bamboo canes and soft ties, or purpose-made support rings. Once a heavy spike has snapped or fallen, it cannot be straightened. Support early. |
| Flowers fade quickly | Drought; very hot weather | Water deeply during dry spells. In very hot weather (above 25°C), the flowers open and fade more rapidly — this is a natural response. Mulch around the base to keep roots cool. Cut for the vase at an early stage — one or two bottom bells just open — and they will last longer indoors in cool water than in the garden heat. |
Plant Specifications
The biennial that has filled June cottage gardens for five hundred years
Canterbury Bells require patience — a quality that annuals never demand — but what they give in return is something annuals cannot provide: the specific height, scale and heritage character of towering bell-laden spires in blue, pink and white that arrive precisely when the garden most needs them in June, and that make bumblebees comfortable enough to sleep inside them overnight. Sow every year in May or June, transplant in September, stake in April, and let the two-year cycle deliver one of the most romantic and most distinctively British of all cottage garden displays.
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