Canterbury Bells (Campanula medium) are prized for their tall, upright flower spikes and distinctive bell-shaped blooms. These ornamentals are a favorite in cottage gardens, known for adding significant vertical interest to a flower bed. Understanding their growth habit is key to successfully incorporating them into a landscape design.
Maximum Height and Typical Spread
Canterbury Bells typically achieve a mature height between 2 and 3 feet (60 to 90 centimeters), making them a dramatic addition to the mid-to-back border of a garden. The plant’s final stature is highly dependent on both its specific cultivar and local growing conditions, with certain dwarf varieties maturing at a much shorter 14 inches.
The plant’s lateral growth, or spread, is modest, generally ranging from 12 to 18 inches (30 to 45 centimeters). This compact spread means the plant maintains a narrow, columnar shape as it grows upward. This allows gardeners to plant them in tight groupings without excessive crowding.
The Biennial Growth Cycle
The tall growth that Canterbury Bells are known for occurs during the second year of the plant’s life cycle, as they are classic biennials. In the first year after sowing, the plant focuses exclusively on vegetative growth, forming a low, dense rosette of leaves close to the ground. This leafy clump gathers and stores energy, which is then used to survive the winter months.
The plant requires a period of cold, a process called vernalization, to trigger the hormonal changes necessary for flowering. Once the plant has successfully overwintered, the stored energy is rapidly mobilized to produce the tall, flowering stem. This vertical surge results in the spectacular blooms and the impressive height that gardeners cultivate the plant for. After flowering and setting seed, the plant completes its life cycle and naturally dies off.
Environmental Factors Influencing Final Size
The ultimate height a Canterbury Bell reaches is significantly influenced by its growing environment. Adequate sunlight is a primary factor, with the plant performing best and achieving maximum height when receiving at least six hours of full sun daily. Insufficient light can lead to a weaker, leggier plant that is unable to support a full display of blooms.
Rich, fertile, and well-draining soil provides the necessary nutrients to fuel the rapid growth spurt in the second year. Poor or compacted soil can stunt the plant, limiting the amount of energy it can store during the first year’s rosette stage. Consistent and adequate watering is also important, as drought stress will cause the plant to prioritize survival over maximum vertical growth.
Supporting Tall Growth
Because of their height and relatively slender stems, Canterbury Bells often benefit from physical support, especially in windy or exposed garden locations. Staking should be implemented early in the second year, ideally before the flower spike begins its rapid ascent, to prevent the mature stems from bending or breaking under the weight of the blooms. Using simple stakes, cages, or growing the plants near shrubby companions offers the necessary reinforcement.
The practice of deadheading, or removing spent flower spikes, can influence the plant’s appearance and may encourage a second, smaller flush of blooms. While deadheading maintains a tidy look and redirects energy away from seed production, it does not increase the plant’s overall, mature height. Allowing some flowers to remain on the stem ensures that the plant can self-seed, providing new rosettes for the garden in the following year.