The most popular campanula or Bell Flower is the trailing Campanula isophylla with blue star-shaped, and its white variety alba. This perennial is a splendid plant for hanging baskets. The other campanula grown under glass is C. pyramidalis, the Chimney Bell Flower, which makes a plant sometimes as much as 4 ft. tall and is often too large for the amateur’s greenhouse. This biennial also has blue flowers and a white variety. Propagation
Campanula isophylla can be raised from cuttings taken at any time between March and September, the best cuttings being made from the young shoots growing from the base of the plant. These can be rooted in a propagating frame in a mixture of equal parts loam, peat and sand or in a soilless seed compost. The temperature required is between 10 and 16°C. (50 to 60°F.). It can also be raised from seed sown in an unheated frame in March or by careful division and repotting of the old plants, also in March. The plants should be grown on in John Innes No. 1 Potting Compost.
Seed of C. pyramidalis is sown in a cool greenhouse or frame in March or April in seed compost. A temperature of 16°C. (60°F.) is needed. The resulting seedlings should be pricked off singly as soon as they can be safely handled into 3-in. pots using John Innes No. 1 Potting Compost. From now onwards they need cool conditions and should be hardened off in a cold frame. The pots can be stood out of doors in summer and overwintered in a cold frame. The plants will finally need pots of 6- to 10-in. size. They come into flower in July and should continue to bloom for many weeks.
As previously mentioned, C. isophylla is an ideal plant for a hanging basket. I value it, too, for trailing along the side of the staging – a picture in summer when the blue or white flowers are borne particularly freely. It will also flower in winter if given a reasonable temperature. I never grow C. isophylla in pots of more than 5-in. size; in fact, I prefer half-pots or seed pans as receptacles for they are less noticeable when placed along the edge of the staging.
C. pyramidalis is useful for placing at the back of a display of flowers, or as a ‘dot’ plant to give variation in height amongst shorter plants.