Canterbury bells are the defining flower of the early summer cutting garden — tall spikes of large, open bell-shaped flowers in blue, purple, pink, and white. They are biennial: sow in early summer to bloom the following year, then compost after flowering. Once you establish a rhythm of annual sowings, you'll always have plants at the flowering stage.
The blooms are among the most showy of any spike flower and last well in the vase — cut when the lower quarter of the spike is open. Self-seeding is unreliable; a fresh sowing each year gives more consistent results.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.