Growing Campanula (Bellflower): A Complete Profile
By Growing Home Greens Team · August 10, 2026
Campanula, also called Canterbury bells, is a tall spring cut flower with a genuine quirk: it’s daylength-sensitive, needing short days as a young seedling to build enough stem length before it flowers under the long days of early summer.
Timing matters more than usual
Direct-seeding isn’t recommended; start seed indoors 6 to 8 weeks before planting out, and don’t cover it since it needs light to germinate. A fine layer of vermiculite over the top helps hold moisture without blocking light. Because of the daylength sensitivity, plants should be started in fall, winter, or very early spring rather than timed to the last frost the way most annuals are. Fall-sown plants that overwinter in an unheated tunnel produce very tall, vigorous growth and bloom in early June; winter-sown plants flower a few weeks later on shorter stems.
Spacing depends on the goal
For single-stem cuts, which finish faster and suit greenhouse production, space 4 to 6 inches apart. For multi-stem, well-branched plants better suited to outdoor growing where space is less precious, space 10 to 12 inches apart; expect 8 to 10 stems per plant with this method. Support is recommended either way.
Harvest and handling
Cut fresh once 2 to 3 of the lower buds on a stem have opened. Keep cut stems upright rather than laying them flat, since the flower spikes bend easily and don’t recover once bent.
Campanula has no well-established companion pairings, and nothing it needs to be kept away from. Given its unusual daylength requirement, it needs a fall or winter slot in the Garden Designer’s seed-starting calendar, well outside the normal spring-sowing window.
Source: Campanula (Bellflower): Key Growing Information, Johnny’s Selected Seeds.
Companion planting guide for Campanula (Bellflower) · Find your planting dates
Typically viable in USDA zones 2-11. Not sure your zone? Look it up by ZIP code.
Mature height: 2.5-3.5 ft
Method: Start indoors: Start indoors from seed, then transplant outside. It needs a head start most zones can't give it by direct-sowing alone.
When to plant campanula (bellflower), by zone
Every zone campanula (bellflower) grows in. Pick your zone in the header and it will be highlighted here. Each zone links to its full page.
| Zone | Start indoors | Sow or plant out | Bloom |
|---|---|---|---|
| 2a & 2b | Apr 1–Apr 8 | May 27–Jun 3 | Sep 24–Oct 1 |
| 3a & 3b | Apr 11–Apr 18 | Jun 6–Jun 13 | Oct 4–Oct 11 |
| 4a & 4b | Mar 27–Apr 3 | May 22–May 29 | Sep 19–Sep 26 |
| 5a & 5b | Mar 22–Mar 29 | May 17–May 24 | Sep 14–Sep 21 |
| 6a & 6b | Mar 7–Mar 14 | May 2–May 9 | Aug 30–Sep 6 |
| 7a & 7b | Feb 20–Feb 27 | Apr 17–Apr 24 | Aug 15–Aug 22 |
| 8a & 8b | Feb 4–Feb 11 | Apr 1–Apr 8 | Jul 30–Aug 6 |
| 9a & 9b | Dec 28–Jan 4 | Feb 22–Mar 1 | Jun 22–Jun 29 |
| 10a & 10b | Dec 12–Dec 19 | Feb 6–Feb 13 | Jun 6–Jun 13 |
| 11a & 11b | Nov 13–Nov 20 | Jan 8–Jan 15 | May 8–May 15 |
Bloom dates are about 120 days after the sow or plant-out date, not after starting seeds indoors.
Zone 2 sows before zone 3 here, which looks wrong and is not. USDA zones rank winter cold, not season length, and zone 2 is mostly interior Alaska, where hard winters come with warm summers. More on what a zone measures.
See exact start-indoors, direct-sow, and harvest dates for your zone →
How many Campanula (Bellflower) plants fit per square foot?
Spacing: 2 per square foot (square-foot-gardening spacing). Mature height: 2.5-3.5 ft.
Varieties worth considering
- 'Champion II White' campanula: Johnny's Selected Seeds' pelleted F1 campanula line, described as uniform and productive for cut-flower use; the pelleted seed makes precise sowing easier given how small campanula seed is. (source)
- 'Champion II Deep Blue' campanula (best for: true blue color): Johnny's Selected Seeds describes this as a uniform, productive cut flower in the same pelleted F1 line as Champion II White, in the deep blue that gives campanula its common name of bellflower. (source)
Why each variety is listed comes from the source shown next to it. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement. The buy links are separate from those sources: they go to seed suppliers that sell that exact variety, and we may earn a commission on some of them.
Where to buy campanula seeds
True Leaf Market (each supplier's campanula seeds)
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See it growing
Search YouTube for "growing campanula (bellflower)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
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Growing Campanula (Bellflower): A tall spring cut flower that's daylength-sensitive, needing short days as a young seedling to build stem length before it flowers well.
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