Clustered Bellflower prefers consistently moist soil, particularly during its active growing and flowering seasons. Water deeply when the top inch of soil feels dry to the touch, ensuring good drainage to prevent waterlogging, which can lead to root rot. During prolonged dry spells, supplemental watering is crucial. Once the plant enters winter dormancy, significantly reduce watering, only providing moisture if the soil becomes completely parched.

Deadhead spent flower clusters regularly throughout the blooming season to encourage continuous flowering and prevent unwanted self-seeding. After the main flush of blooms has faded, cut back the entire plant by about one-third to one-half. This rejuvenation pruning can stimulate a second, smaller flush of flowers and maintains a tidy appearance. In late autumn, cut back all foliage to the ground as the plant prepares for winter dormancy.

Campanula glomerata can be easily propagated by division in early spring or autumn. Carefully dig up the clump and separate it into smaller sections, each with healthy roots and shoots, then replant immediately. It can also be grown from seed sown directly outdoors in spring or autumn, or started indoors 6-8 weeks before the last frost. Softwood cuttings can be taken in late spring or early summer, though division is generally more reliable.

Repot container-grown Clustered Bellflower every 2-3 years in early spring to refresh the soil and provide more room for root growth. Choose a pot that is one size larger than the current one, ensuring it has adequate drainage holes. If the plant has become root-bound, gently tease out the roots before repotting. For mature plants, root pruning and replanting in the same pot with fresh soil can also be an option.