Gardeners looking for a true blue color in a flower can’t go wrong with the old-fashioned annual cornflower. These fully double flowers look like miniature carnations with small 1 1/2-inch blooms, only they’re much easier to grow.
Originally, Centaurea cyranus was a native European and Asian grassland/pasture flower, but it was largely eradicated by the use of modern herbicides. As befits its heritage, cornflower can easily escape and naturalize rampantly if not kept in check. Nevertheless, every gardener needs at least one can’t-fail plant in the flower garden, and this lightly fragrant flower belongs in every beginner’s landscape.
The quick-growing flowers will reach a height of up to 48 inches and a spread of up to inches in all growing zones. The flowers are dense 1 1/2-inch blooms that appear from last spring through midsummer. The species plant has bright blue flowers, but there also are cultivars offering pink, white, and crimson flowers.
Cornflower can be planted in spring by seeds or nursery transplants around the time of last frost. It can take as much as three months for seeds to sprout and reach flowering maturity, so for quicker flowering in colder climates, seeds are often started indoors six to eight weeks before last frost.
|Botanical Name||Centaurea cyanus|
|Common Name||Annual cornflower|
|Plant Type||Flowering annual|
|Mature Size||12–48 inches tall, 10–12 inches wide|
|Sun Exposure||Full sun to part shade|
|Soil Type||Average, well-draining soil|
|Soil pH||7.2 to 7.8 (slightly alkaline)|
|Bloom Time||Late spring to mid-summer|
|Flower Color||Blue, purple, pink, or white|
|Hardiness Zones||2–11 (USDA)|
Like most common annuals, cornflower can be purchased as nursery transplants, but they are also very easy to grow from seeds. Cornflower are as easy to maintain as they are to start. Stake plants if they flop, which is usually more of a problem in shaded gardens. Alternatively, you can grow them among other sturdy perennials like coneflowers that will act as natural supports for the stems.
Cornflowers typically bloom for about 10 weeks, from May to mid-July, but deadheading them extends and increases the blooming. You can seed additional times spaced every two weeks to extend the bloom time. Cornflowers makes excellent dried flowers if you cut the blossoms before they begin to wilt.
As frost kills the plants, pull up the plants to remove debris that can foster fungi or serve as nesting areas for pests. Or, you can remove the plants when the bloom time has ended to open up space for late-season plants.
Cornflowers are a versatile flower with many uses in the landscape and in the home:
- Consider adding cornflowers to the ornamental vegetable garden, as their nectar content will attract pollinating insects that boost the yields of tomatoes, squash, and other plants that rely on pollinators.
- Cornflowers produce edible flowers, so you can include them in the kitchen garden to jazz up salads. Some describe their taste as sweet or cucumber-like. Cornflowers have a long tradition in herbal and natural medicines as an anti-inflammatory so you can include them in the herb garden too.
- Cornflowers are a natural choice for wildflower gardens, and their bright blue blossoms are highly appealing to bees and butterflies. Avoid spraying any pesticides around cornflowers, even organic pesticides, which are still harmful to bees and other beneficial insects.
- Popular as an inexpensive and renewable source of blue flowers in wedding bouquets, cornflowers are also welcome in the home cutting garden. Pair blue cornflowers with annuals opposite on the color wheel, like orange cosmos or yellow marigolds, to make both flowers stand out in the flower garden.
Cornflowers suffers from no truly serious insect or disease problems. In wet, humid conditions they can experience fungal problems, and aphids and mealybugs sometimes appear.
Cornflowers prefer full sun, but they'll still do well with a bit of shade in the afternoon. Shady conditions can make the plants leggy and prone to flopping, which may require staking.
Provide average, well-drained garden soil. Unlike many garden flowers, Cornflowers prefer soil on the alkaline side, with a pH of 7.2 to 7.8. You can add crushed limestone to garden beds if your soil is on the acidic side.
Give cornflowers the equivalent of 1 inch of water per week, especially in the hottest months of July and August.
Temperature and Humidity
When it comes to temperature, cornflowers are fairly agreeable, tolerating both light freezes as well as the hottest summer days. They'll tolerate humidity, but keep a close eye on them in these conditions, as it leaves them susceptible to fungal disease.
- 'Blue boy' has flowers that are a vivid periwinkle blue.
- 'Tall Double Mixed' series offers plants in shades of white, pink, and blue.
- 'Blackball' is a rare variety with flowers featuring deep crimson poms.
- 'Dwarf Blue Midget' begins blooming when plants 6 inches and top out at 12 inches, making it excellent for containers.
- 'Burgundy Beauties Mix' includes plants producing three types of blooms: burgundy-white bicolor flowers, solid burgundy flowers, and burgundy flowers with white tips.
Centuarea Cyranus vs. C. Montana
Centaurea cyanus plants have been cultivated for centuries, and have picked up many common names along the way, including cornflowers, basket flower, bluebonnet, blue bottle, blue bow, blue cap, boutonniere flower, and hurt sickle. To add confusion, there also perennial species in the Centaurea genus that look very similar and also carry the common name of cornflower. One such plant is C. montana, a very common garden perennial.
Although the species are sometimes confused with one another, when viewed side by side the differences are apparent. C. montana, the perennial species, has the same rich blue color as the annual C. cyanus, but the flowers have single petals that give them a wispy appearance, and they have a darker, reddish purple center not found in the annual cornflower. The lance-shaped leaves are fuller than those of the annual cornflower, and the plants are generally a little shorter in stature. And perennial C. montana ends its bloom season a little earlier than C. cyranus.
As you might expect from a plant that self-seeds so readily, there is no great challenge to propagating cornflowers. The easiest way is to simply collect seeds from the dried flower heads and store them until planting time.
It is also relatively easy to dig up and transplant any self-seeding volunteers that spring up in the garden in the spring—a common phenomenon if you haven't carefully deadheaded spent flowers the previous season.
How to Grow Cornflowers From Seed
You can buy packets of 200 cornflower seeds for less than five dollars, making this a great flower choice for frugal gardeners. Even if you aren’t used to growing plants from seed, you have a high chance of success starting cornflowers.
Sow in late winter or after the first frost, directly in the garden. Don't be too concerned about planting too early; Mother Nature will tell the seeds when to germinate. Cover seeds with about 1/2 inch of soil. Keep the seedbed moist until germination occurs, usually within 10 days in warm temperatures. Cornflowers can tolerate some crowding, but thinning seedlings increases blooming and vigor in plants.
If you choose to start seeds indoors to ensure early flowering, do so six to eight weeks before the last expected frost. Use seed-starter mix or ordinary potting soil in a seedling tray, and keep the soil moist and warm until they sprout, then grow in a bright location or sunny window until outdoor planting time.
At the end of the season, you can collect the brown seed pods and extract the seeds to sow in other areas or to share with friends. Expect more cornflower flowers in the same site next year, as they volunteer freely.