Centaurea cyanus. Upright 2-3 foot annual plants produce abundant flowers. Loved by bees, the plant prefers full sun and thrives in any well-drained soil. Best sown direct. Also known as "Cornflower" and "Bluebottle", it is the national flower of Estonia. In herbalism, a decoction of cornflower is effective in treating conjunctivitis, and as a wash for tired eyes.