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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, dahlia, Russian sage, and other colorful mid- to late-season blooming perennials.
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garden plans for Centaurea
Centaurea Care Must-Knows
Full sun or partial sun 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 planted directly in the garden. Annual varieties are quick to emerge when started outside. Simply sow seeds about ½ inch deep in good garden soil. 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.
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 two to three 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.