How to Grow and Care for Cornflower

Flower gardeners can’t go wrong with the old-fashioned annual cornflower (Centaurea cyranus). This plant's double 1 1/2-inch blooms resemble miniature carnations and are easy to grow. Originally a native European and Asian pasture flower, cornflower was largely eradicated in its natural habitat by the use of modern herbicides. It can reseed rampantly if not kept in check. Nevertheless, every gardener should have at least one "can’t-fail plant" in their garden, and the lightly fragrant cornflower is perfect for beginners.

Cornflower's delicate papery discs are surrounded by bracts that flower atop slim stems of narrow gray-green leaves. Mature plants will reach a height of up to 48 inches, and a spread of 12 inches wide in all growing zones. Dense bright blue blooms last from spring through midsummer. This species also boasts several cultivars offering pink, white, and crimson flowers.

Cornflower Care

Cornflower is a versatile plant with many uses in the landscape and in the home. Consider adding it to an ornamental vegetable garden, as the nectar content will attract pollinators that boost the yield of tomatoes, squash, and other plants that rely on them. Add cornflower to a wildflower garden to attract bees and butterflies. Or, include blue cornflower in a cutting garden paired with annuals like orange cosmos or yellow marigolds.

Like most common annuals, cornflower can be purchased as a nursery start, but it is also very easy to grow from seed.  Grow it among other sturdy perennials, like rudbeckia or coneflower, that will act as natural supports for the stems. You can also stake the plant to avoid flopping.

Cornflower typically blooms for about 10 weeks (from May to mid-July), but you can increase the bloom time by deadheading spent flowers. Seeding the flower on a spaced-out schedule of every two weeks will also extend bloom time. Cornflower makes an excellent cut or dried flower. Cut the blossoms in their prime before they begin to wilt.

Light

Cornflower prefers full sun but it will tolerate a bit of shade in the afternoon, especially during the dog days of summer. Shady conditions all day cause the plant to grow leggy and prone to flopping.

Soil

Cornflower grows best in rich, well-drained garden soil, on the alkaline side, with a pH of 7.2 to 7.8. If your soil tends toward acidic, add crushed limestone to your garden beds

Water

Cornflower needs the equivalent of 1 inch of water per week, especially during the hottest months of July and August. Allow the soil to dry slightly in between waterings, but don't let it dry completely or the plant will flop. If this happens, a good, thorough drink will usually perk it up.

Temperature and Humidity

When it comes to temperature, cornflower tolerates both a light freeze as well as a hot summer day. This plant thrives in 60 F to 80 F temperatures, but may need 85 F to 95 F to reach flowering maturity. Cornflower grows best with an average humidity range of 30 to 50 percent. Keep a close eye on your garden during humid spells, though, as this plant is susceptible to fungal disease under these conditions.

Fertilizer

Iif your soil is poor, fertilize your cornflower monthly with diluted liquid manure or compost tea. Start fertilizing in the early spring when the baby plants are 6 inches tall, and continue throughout the summer. If you have rich soil, you don't need to feed your flowers at all. Often mixing a bag or two of compost into the soil before sowing is enough for the entire season.

Types of Cornflower

Most people are drawn to traditional vibrant blue cornflowers. You'll often see this variety cropping up along roadsides or in the pastures of rural areas. However, other cultivars lend an equally attractive appeal, blooming in colors of white, pink, or red.

Below are a few of the favorites:

• An heirloom variety, 'Blue boy' boasts thistle-shaped flowers of periwinkle blue. Plant this variety early in the spring for a show-stopping landscape display.
• The 'Tall Double Mixed' series provides a great option for a cutting garden, as the blooms of white, pink, and blue make attractive dried arrangements.
• The striking 'Blackball' variety provides an nontraditional option, complete with crimson poms that hold nectar coveted by birds.
• 'Dwarf Blue Midget' works well in beds and borders and begins blooming when the plant is 6 inches tall. This variety tops out at 12 inches, making it an excellent choice for containers.
• The 'Burgundy Beauties Mix' includes plants that produce three colors of blooms: burgundy and white bicolor flowers, solid burgundy flowers, and burgundy flowers with white tips.

Pruning

While not necessary for proliferation, pruning a patch of cornflower can extend its bloom time. To do so, trim the long stems back to the secondary stems once the plants' first flowering period is over (usually around mid-summer). After the second bloom, cut the plants back to the ground or you can pull them out from the roots to open up space for late-season plantings.

How to Grow Cornflower From Seed

As you might expect from a plant that self-seeds so readily, it's easy to propagate cornflower from seed. You can collect your own seeds from dried flower heads and store them over the winter until planting time. Or, you can also buy large, inexpensive packets of cornflower seeds.

Here's how to grow cornflower from seed:

1. Sow seeds in late spring directly into the garden after the last frost. (Don't be concerned about planting too early; Mother Nature will tell the seeds when to germinate.)
2. Cover the seeds with 1/2 inch of soil and keep the seedbed watered and moist until germination occurs (usually within 10 days in warm temperatures).
3. Once sprouted, thin the seedlings to increase both blooming and vigor in the plants.

You can also start seeds indoors to ensure early flowering. Do so six to eight weeks before the last expected frost using a seed-starter mix in a seedling tray. Keep the soil moist and warm until the seedlings sprout, and then grow them in a bright location or sunny window until it's safe to transplant them outdoors.

Potting and Repotting Cornflower

When growing cornflower in pots or containers, make sure to keep the soil on the dry side to mimic pasture conditions. Porous clay or terracotta pots are best. Choose well-drained soil with perlite, or use a soilless medium made from organic material (similar to a cactus potting mix). Deadhead your potted cornflower for a tidy appearance, and be prepared for a short flowering season when grown this way.

Common Pests & Plant Diseases

An annual with a short growing season, cornflower rarely suffers from serious insect or disease problems. Still, when kept in wet, humid conditions, powdery mildew can occur late in the season, appearing as white spots on the leaves. This fungus rarely kills the plant and treatment is usually not necessary since the plant's lifecycle is short-lived anyway.

Aphids and mealybugs rarely, but sometimes, appear on a crop of cornflower. Control them by reducing the population with bursts of water from the garden hose. Avoid spraying pesticides around cornflowers, even organic ones, as both are harmful to bees and other pollinators that feed on them.

How to Get Cornflower to Bloom

Cornflower blooms best in bright and sunny conditions, so make sure to always plant your crop in an area that receives a lot of sun. Deadheading may encourage more flowering, but with this particular annual, the practice is deemed unnecessary. If your cornflower is not showing blooms due to insufficient light, the only thing you can do is plan better next year and seed them in a sunnier spot.

Common Problems with Cornflower

Although rare, cornflower can fall victim to fungal infections when overwatered and crowded. Make sure to adhere to watering recommendations and thin seedlings to allow for proper airflow around the mature plant. In drought conditions, cornflower is prone to wilting, which can cause your crop to fall over and look unsightly. Usually, a good drink is all that is needed to perk them up.