Prized for its blue petals, the centaurea plant group includes annual species such as bachelor’s button and cornflowers, and a perennial plant commonly called mountain bluet. All three types are prolific nectar producers that attract butterflies. As a vivacious late-spring and early-summer bloomer with the casual growth habit of wildflowers, centaurea suits cottage gardens, wildflower plantings, and cutting gardens. Pair centaurea with daylilies, dahlias, Russian sage, and other colorful mid- to late-season blooming perennials.
Centaurea Care Must-Knows
Full sun or part shade and average garden soil are all that centaurea needs to thrive. Both annual and perennial species tolerate a wide range of soils, from quick-draining sandy soil to heavy clay. In hot regions, plant centaurea where it will receive shade from intense mid-day sun.
Centaurea is easy to start from seed indoors or when sown directly in the garden. Annual varieties are quick to emerge when started outside. Simply sow seeds about ½ inch deep where you want them to grow. Keep the seedbed moist until germination in about 7 to 10 days. When the annual centaurea seedlings reach about 6 inches tall, thin them so they stand 6 to 12 inches apart. This close spacing allows the tall cultivars to support each other, which helps all plants remain upright. Perennial seeds require 15 to 30 days to germinate. When thinning these seedlings, space them 24 to 36 inches apart.
Related: The Easiest Seeds to Start
Start centaurea seeds indoors about a month before the average last frost in your area. Sow seeds in individual peat pots or seed-starting flats filled with commercial seed-starting mix. Cover the seeds with a ½-inch layer of soil mix, and spritz with water to moisten the soil. Transplant seedlings into the garden when they are about 4 inches tall.
Annuals may self-seed. Contain the spread by deadheading, but understand this process will deprive birds of the much-loved seeds. Perennial centaurea spreads very quickly; control its growth in a garden bed by digging up and dividing the plants every 2-3 years.
Drought-tolerant centaurea rarely needs supplemental watering after it establishes a strong root system. In fact, too much moisture can weaken the plant's stem and cause it to become floppy. Snip away spent blooms to spur plants to produce new flowers.
Whether annual or perennial, centaurea often takes on a bedraggled look in midsummer. Foliage will wilt and turn shades of light green and yellow. Rejuvenate plants by cutting them back by one-third or half. If moderate-to-cool weather prevails, expect centaurea to send up fresh foliage and flower stalks.
More Varieties of Centaurea
'Amethyst in Snow' mountain bluet
Centaurea montana 'Amethyst in Snow' combines the best of the white and blue forms of the species. A central purple head is set off by pure-white ray flowers.
Centaurea macrocephala, also known as Armenian basket flower, is indeed a large plant, growing 4-5 feet tall with bright yellow, thistlelike flowers in midsummer. It is hardy in Zones 3-8.
Centaurea montana is a North American native flower with gray-green foliage and cornflower blue blooms in spring to early summer. It reblooms in midsummer if cut back after bloom.
White mountain bluet
Centaurea montana 'Alba' is similar to the species, but with white flowers instead of blue ones.
Centaurea uniflora, as its common name suggests, bears solitary purplish-pink flowers on a mound of prickly green leaves 15-20 inches tall. It is hardy in Zones 4-8.
Centaurea Companion Plants
Poppies' papery, almost artificial-looking flowers are well-loved, and there are a surprising number of different kinds. The finer species including Iceland, Alpine, and Atlantic poppies have a special charm with flowers in myriad colors in spring. Oriental poppies are bristly and less refined, but they have huge, exploding flowers of brilliant reds, pinks, white, oranges, and plum, some with double flowers in summer. Most are blotched with black at the base and centered with a boss of black stamens. After these plants give their all at bloom time, the foliage dies back and looks ragged, so plan to fill the newly available space with annuals, dahlias, baby's breath, or other later-blooming plants.
With its tall wispy wands of lavender or blue flowers and silvery foliage, Russian sage is an important player in summer and fall gardens. It shows off well against most flowers and provides an elegant look to flower borders. The aromatic leaves are oblong, deeply cut along the edges. Foot-long panicles of flowers bloom for many weeks. Excellent drainage and full sun are ideal, although very light shade is tolerated. Plant close to avoid staking since the tall plants tend to flop.
Brightly colored butterfly weed is a butterfly magnet, attracting many kinds of butterflies to its colorful blooms. Monarch butterfly larvae feed on its leaves but seldom harm this native plant. It is slow to emerge in the spring, so mark its location to avoid accidental digging before new growth starts. If you don't want it to spread, deadhead faded blooms before seedpods mature. It is sometimes called milkweed because it produces a milky sap when cut.