Samantha Lahman, University of Minnesota Extension Horticulture Intern, Douglas County
Centaurea cyanus, more commonly known as the annual Bachelor Button or Cornflower, is in full bloom in the garden this summer. Cornflowers are easy to grow and come in a great variety of colors, which has made them a long time favorite for novice and experienced gardeners. The Cornflower received its common name from the flowers that bloom wildly in the grain fields of southern Europe. It is even rumored that the Cornflower was selected as Germany's National Symbol of Unity because Queen Louise of Prussia; upon fleeing Germany to escape Napoleon, reportedly hid her children in a cornfield and kept them quiet by weaving Cornflowers into wreaths.
Cornflowers are tall annuals that grow on beautiful grey-green stems. The most common color is a bright blue (Blue Boy), but other varieties range from pinkish white to deep maroon. Growing to a height of 24-36 inches, they can be easily placed in gardens of any size and are beautiful fillers along borders. They are also useful in cut flower gardens and are commonly included as dried flowers in everlasting arrangements. For an unusual twist, use their edible blooms to add color to salads and other dishes. Along with their aesthetic and tasteful qualities, Cornflowers are often used to attract bees, butterflies, and birds.
Cornflowers have become such a staple due to their prolific nature. Even the most inexperienced gardeners can grow them successfully. These plants thrive in full sun, but can also grow in partial shade. They prefer moist, well drained soils and will grow well in soil pH levels ranging from 6.6 to 7.8. They are also moderately cold tolerant and can endure temperatures that reach into the low 40s.
Cornflowers are most commonly grown from seed. Sow cornflowers in the spring, approximately 1 to 2 weeks before the last frost. Planting at this time will give you early spring blooms. Germination can be expected in 7 to 10 days. Seeds should be sown 1/4" deep and placed 1" apart .For earlier blooms, start seeds indoors about one month prior to the frost free date. When starting your seeds indoors sow 3 to 4 seeds per pot and cover the seeds with a 1/2" layer of the mix because centaureas need darkness to germinate. Cover your pots with plastic wrap, or a clear plastic dome to retain soil moisture and humidity. When seedlings emerge, remove the plastic covering to avoid overheating and leaf burn. Once your cornflowers are approximately 2 inches tall, transplant outside in your chosen garden location. For optimum success, transplant your seedlings on a calm, overcast day. While these plants are known to be tough, it is easier on the plants if they aren't immediately exposed to excessive heat and damaging winds. Remember to water immediately following transplanting. When seedlings are 1 to 2 inches tall, thin to 6 to 8 inches apart. Cornflowers bloom for approximately one month. If you wish to have an extended blooming season, consider successive plantings. Planting every two weeks will insure that your blooms last the summer.
After they are established, watering should be done infrequently. Yes, infrequently. Another charming quality of cornflowers is that they are extremely drought tolerant. When over watered, the cornflower's stems will become droopy and soft. As with most flowers, remember to trim dead and expiring blooms to encourage the growth of new blooms. Cornflowers are generally pest resistant. The most common pest to invade Cornflowers is the aphid. To control aphids, you can spray them off with a garden hose or apply an insecticidal soap. These little flowers are also very resistant to diseases and fungi. Extremely wet weather leads to fungal problems such as: rust and powdery mildew. To help prevent fungal infections, water at the base of the flowers so as not to get the leaves wet, and remove any leaves or stems that you suspect are infected. Use fungicidal soap or garden sulfur to control rust on plants.
Before investing your area of garden to cornflowers forever, by planting centaurea Montana, the perennial version of centaurea, take into consideration that while Centaurea cyanus is an annual, this does not mean that you will need to replant year after year. Many times cornflowers will re-seed. To encourage this natural re-seeding, leave the last blooms of the growing season on the plants.
I adore blue in the garden, and am always looking for new and unusual "blues" to add. However, my staple "blue" is the prolific cornflower. If you also love "the blues", and are looking for attractive, multi-use blossoms, cornflowers are the way to go.
"The blues tells a story. Every line of the blues has a meaning."
John Lee Hooker
Samantha Lahman is the 2011 Summer Intern for the Horticulture Extension in Douglas County. This summer she has been busy writing the "Growing Green" newspaper column for local newspapers, diagnosing plant problems, identifying bugs, updating the West Central Gardener Facebook page, and creating a workshop for the Douglas County Master Gardeners to use in the future on "Growing Your Own Meadow Garden." Samantha will be a senior this year at the University of Minnesota, Crookston. Her major is Animal Science with minors in Communication and Agricultural Business. After college she hopes to work either for the U of M Extension in the 4-H and Youth Development areas or Public Relations for one of the Minnesota livestock associations.