How to sow and care for Canterbury Bells | Garden guide to Campanula medium

How to grow Campanula medium

Campanula medium, commonly called Canterbury Bells or bellflowers, are beautiful, trendy, and an excellent cut flower with a long vase life. They symbolize gratitude and faithfulness. In gardens, they are best grown en masse in borders or among shrubs. It prefers cool or warm zones and is native to mid and southern Europe; not suitable for the tropics or hot, dry regions. It thrives in lightly shaded to sunny locations in well-drained soil. Keep well watered.

The Campanula is native to middle and southern Europe, where it establishes itself in the mild winters, flowering with its beautiful bell-shaped flowers the following summer. 

Canterbury Bells key details

  • Height at maturity: 60-100 cm (depending on the variety)
  • Spread at maturity: 20-40 cm (depending on the variety)
  • Light needs: Full sun to part shade
  • Hardiness: USDA Zones 3-9
  • Type of soil: Moist, fertile, well-draining
  • Soil pH: 5.8 – 6.2
  • Where to plant: Flower beds, borders, and containers
  • Features: Annual
  • Pruning: 3-4 weeks after germination, you can gently pinch back your plants as they begin to elongate vertically
  • Best time to sow seeds: August-February
  • Flowering period: January-June
  • Common names: Cup and Saucer
  • Plant type: Annual
  • Difficulty: Easy

Starting your Campanula seeds

Stage One: Sow your seeds indoors from fall until mid-February. Cover the seed lightly with vermiculite and maintain high humidity. Keep the room temperatures at 15-18°C. Germination takes about 3 weeks.

When 5-6 leaves open, plant out at a 25 cm distance (16 plants/m²); sunny and cool growing conditions. You can also start to introduce them to cooler temperatures (13-15°C).

Stage Two (days 11-21): After the seedlings emerge, place the plug flats in a bright and cool greenhouse with good air circulation. Apply a light feed of 100 ppm Nitrogen using a well-balanced fertilizer. Maintain moderate air temperatures, 68-72°F/20-22°C, to avoid stress and prevent rosetting*.

Stage Three (days 22-34): Seedlings are beginning to fill in the plug tray. Fertilize as needed to maintain a media EC of 0.7 to 1.0 mmhos (1:2 slurry) using a well-balanced fertilizer. The use of Calcium Nitrate-based fertilizer is beneficial in helping to build strong and healthy transplants.

Growing on

Stage Four (day 35) Seedlings should now have 2-3 true leaves and are now ready to transplant into cut flower beds. Campanula medium as a species possesses a tap root structure and root-bound plants will not produce a healthy and strong plant. In order to maximize stem length do not delay transplanting.

*induced dormancy caused by stressing the plugs (uneven moisture, excess fertilizer, chemical damage, delayed transplanting, night temperature above 77°F/25°C, or insufficient lighting during flower bud initiation. Maintain the day temperature below 82°F/28°C and the night temperature below 72°F/22°C.

Transplanting to flowering – 14 weeks

Site preparation: Select a bed with good drainage and soil that is high in organic matter. For best results provide full sun and good ventilation.

Plant Spacing:

  • Single Stem*: 4 – 6 inches/10 – 15 cm. apart
  • Multi Stem**: 10 – 12 inches/25 – 30 cm. apart

*single stem production will crop more quickly and is recommended for greenhouse production.
**multi-stem production is best for outdoors or in a cold frame.

Expect 8-10 stems per plant.
Note: After transplant do not allow the plants to dry out in order to prevent tip burn.

Temperature: Ideal growing temperature is 55–60°F/ 13–15°C.

Fertilizer: Campanula is not a heavy feeder. Use a well-balanced calcium nitrate-based feed to maintain a soil EC of 0.7 to 1.0 mmhos (1:2 slurry). A lack of boron will cause distortion and tip abortion. A lack of iron will cause tip burn on the leaves.

Support: Support is recommended to avoid damage to plants during windy periods; especially for single stem production.

Lighting: Campanula is a long-day responsive plant and will require lighting for winter flowering. Light the plants when they have 8 to 10 true leaves, (4 to 5 weeks after transplanting), using “mum lighting” from 10 pm to 2 am for 40-45 days. No supplemental lighting is required for a late spring flowering (transplanting in mid February).
Note: Provide short day conditions (>12 hours) from sowing until 4-5 weeks following transplant to ensure sufficient vegetative growth.

Crop time: In general, Campanula flowers in 130-150 days from sowing using the above culture. An early August sowing will yield cut flowers in late December to early January if the night temperature is maintained at a minimum of 50°F/10°C on the growing point and the crop is lighted for 40-45 days starting 4 to 5 weeks after transplanting. For late spring to early summer flowering from a February sowing, no day length manipulation is necessary.

*In cold winter areas, some growers have been successful transplanting plugs into outdoor beds in September and over- wintering them to produce 40 inch/100 cm. spikes the following spring. Results vary so trial first.

**In mild temperature regions, (Coastal California, Oregon, Washington, Alaska) year round production is possible with a black out system. During long day conditions (sowings from late February to Late July), maintain short day conditions (less than 12 hours) in the plug stage continuing until 4-5 weeks after transplanting and keep optimum production temperatures.

Harvesting

Cut stems when two or three lower buds are open. Place stems in tepid water and keep in a cool spot in an upright position to avoid stem bending. Beekeepers use Canterbury Bells for making potently sweet honey.

Post-harvest care: The best vase life is achieved by placing stems in 100°F/38°C water and a 5% sucrose pulse for the first 24 hours.