This grower is sure of this plant identification.
Serbian bellflower, Bellflower
Campanula poscharskyana (Serbian bellflower). This species is a beautiful low-growing perennial which will produce bright green leaves with blue-mauve showy flowers that will appear in late spring and early summer. They are ideal as low edging for the front of a perennial border.
They are fully to half hardy and are grown in the sun or shade. Most of the species will prefer moist but well drained soil. Delicate flower colours are preserved best in shade.
Border, rock garden, ground cover, walls. Spring/Autumn interest.