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Clustered bellflowers (Campanula glomerata) are a beautiful shade of dark purple.
I would grow more of these pretty perennials if they had a longer blooming season. They typically bloom in June and July for about 4 to 6 weeks. If you can find plants that bloom at the same time you can make some spectacular color combinations.
There are quite a few clustered bellflower cultivars ranging in height from 18 to 36 inches tall. The plants prefer sun to part-shade and make good cut flowers.
I grow ‘Odessa’ which reaches 2 to 3 feet tall with dark-purple, upfacing blooms:
