How to Prune chimney bellflower?
No pruning required

chimney bellflower · Campanula pyramidalis
Also known as: chimney bells; chimney plant; pyramidal bellflower; steeple bellflower; steeple bells
Will grow well in fertile, neutral to alkaline soil that is moist but well-drained, in full sun or partial shade avoiding wet conditions in winter. A semi-shade position will ensure the best flower colour is preserved.
No pruning required