Bachelor buttons, with their vibrant blooms, are cherished garden additions, known for their charming, old-fashioned appeal. Their delicate, fringed flowers and graceful presence suit various garden styles, from informal cottage gardens to structured borders. These versatile plants often appear in traditional floral arrangements and as boutonnieres.
The Core Question: Annuals vs. Perennials
Whether bachelor buttons are annuals or perennials depends on the specific species. The plant commonly recognized as the bachelor button or cornflower, Centaurea cyanus, is an annual. This means it completes its entire life cycle within a single growing season, growing from seed, flowering, producing new seeds, and then dying.
In contrast, other plants within the Centaurea genus are perennials, living for more than two years. A prominent example is Centaurea montana, also known as mountain cornflower or mountain bluet. While both Centaurea cyanus and Centaurea montana share similar blue flowers, their distinct life cycles require different cultivation and garden planning approaches.
Distinguishing Between Bachelor Button Types
Distinguishing between annual and perennial bachelor buttons involves observing physical characteristics and growth habits. The annual Centaurea cyanus grows with delicate, slender stems and finely cut, gray-green, lance-shaped leaves. Its flowers are double and resemble miniature carnations, appearing in various colors including blue, pink, purple, and white. Annual bachelor buttons are prolific self-seeders, readily dropping seeds that can germinate and grow new plants in subsequent seasons, sometimes giving the impression of perennial growth.
In contrast, the perennial Centaurea montana presents a more robust, clump-forming growth habit with broader, gray-green, lance-shaped leaves up to 7 inches long. Its flowers are larger, a rich blue or violet, with fringed petals and a distinct reddish-blue, thistle-like center. Unlike annuals that produce many flower heads on branched stems, Centaurea montana bears a single flower head, or occasionally up to three, per stem.
Growing and Care Considerations
Cultivating bachelor buttons requires understanding the specific needs of annual and perennial types. Both varieties thrive in full sun, though they can tolerate some light shade, especially in hotter climates. They prefer average, well-drained soil; annuals tolerate poorer conditions, while perennials appreciate moist, well-drained soil and can be drought tolerant once established.
For annual Centaurea cyanus, consistent watering is beneficial, especially during dry periods, though established plants endure some drought. Deadheading spent flowers regularly encourages continuous blooming throughout the season and extends their flowering period into autumn. To allow self-seeding for the following year, let some flowers remain on the plant and go to seed.
Perennial Centaurea montana is adaptable and grows in various soil types, including sandy, clay, or stony soils, tolerating a range of pH levels. These plants can spread rapidly by stolons or rhizomes, forming colonies, so managing their spread may be necessary. To maintain vigor and control growth, dividing perennial bachelor buttons every two to four years in spring or autumn is recommended. Deadheading spent blooms on perennials also encourages a second flush of flowers later in the season and prevents excessive self-seeding.