Bachelor's Button, Montana Overview Category: Perennials Common Name: Bachelor's Button, Montana Botanical Name: Centaurea montana 'Blue' Sun Exposure: Full sun Height: 24 in. Spread: 24-36 in. See notes | Back to perennials Notes Cornflower-blue, fringed blossoms. Attract butterflies. Blooms from early to midsummer and usually reblooms. This species is a low, spreading. Great planted in mass where the blue flower display has the most visual impact.