Cornflower Growing Guide and Care Tips

It’s hard to go wrong when you put old-fashioned cornflowers in your garden. It produces 1 ½-inch double blooms that look a lot like miniature carnations, and they’re very easy to grow and maintain. They were originally a native Asian and European pasture flower, and cornflower was naturally eradicated from the natural habitat using modern herbicides. If you don’t keep it in check, it can run rampant. However, it’s always a good idea to have one “never fail” plant in your garden, and the lightly fragrant cornflower is a perfect pick.

The delicate papery discs on the cornflower get surrounded by bracts that will flower and sit on top of slim stems with grayish-green, narrow leaves. Mature plants get up to 48 inches high, and they can spread up to a foot wide in every growing zone. The bright blue, dense blooms will last from spring until the middle of summer, and there are several cultivars available in shades of white, pink, and crimson.

Cornflowers introduce vivid color into your garden, but you have to curb their growth as they will take over the space.

Cornflower – Quick Overview

Attracts:	Bees, butterflies, goldfinches, hummingbirds, pollinators
Bloom Time or Season:	Summer
Common Diseases:	Root rot, powdery mildew, wilting, and stem rot
Common Pests:	Aphids, mealybugs, and leafhoppers
Companion Planting:	Black-eyed susan, bee balm, daisy, phlox, snapdragon, and coneflower
Exposure:	Full sun
Family:	Asteraceae
Foliage & Flower Color:	Greenish-silver and pink, blue, red, purple, and white
Genus:	Centaurea
Grow Rate:	Fast
Hardiness Zone:	2 to 11
Height:	One to three feet
Maintenance:	Low
Native to:	Europe
Order:	Asterales
Planting Depth:	¼ inch for seeds
Plant Type:	Reseeding annual
Soil Drainage:	Well-draining
Soil pH:	6.6 to 7.5
Soil Type:	Average
Spacing:	One to three feet
Species:	Cyanus
Spread:	One to two feet
Tolerance:	Drought
Uses:	Borders, beds, cutting gardens, cottage gardens, mass plantings, drifts, xeriscaping, and wildflower gardens
Water Needs:	Moderate

How Cornflowers Look

Cornflowers are a recognized naturalizing flower, and it belongs in formal estate gardens and cottage gardens alike. Wherever you want to plant these clump-forming, colorful plants, they will add color and structure to your space. More importantly, this plant is a huge attractant to a broad range of garden wildlife.

The cornflower falls into the Centaurea family from Europe. This is an annual genus with perennials too, and you grow them for the unique thistle-like flower heads. Some of the most popular cultivated species of cornflower have purple thistle-like flowers. Each head gets encased with a ring of the most slender, brightest blue petals. Together, the flower heads can resemble a mass of stars when they’re all in bloom.

The foliage on this plant offers the same thistle-like appearance. It has a vigorous growth habit while being grayish-green in color, and it is covered in thousands of tiny silver hairs to make it look furry. The leaves are ovate and long, and they’re not serrated like thistle is. They also come with a noticeable mid-rib. As this is an evergreen plant, the foliage will keep the silvery-gray coloring all year-round.

Other cornflower cultivars have different flower colors. Some are white or pink, or blue and purple are also popular. They all have very similar foliage, and we’ll outline a few different options below.

The unique look of the cornflower plant makes them a favorite with gardeners to add texture and color.

Popular Types of Cornflowers

Most people pick out the traditional bright blue cornflowers, but it’s common to see a variety of plants popping up in pastures or along roadsides in rural areas. However, there are other cultivars that are just as attractive in pink, white, and red hues. A few fan-favorites include:

• Blackball – this is a more nontraditional cornflower that has crimson poms that are full of nectar that draw birds in.

• Blue Boy – The thistle-shaped flowers come in periwinkle blue, and you want to plant this cultivar early in the spring to get a show-stopping look.

• Burgundy Beauties Mix – This group includes plants that produce three colors when it blooms, including solid burgundy flowers, white and burgundy bicolor flowers, and burgundy blooms with bright white tips.

• Dwarf Blue Midget – This cultivar is planted in borders and beds, and it starts to bloom when the plant reaches six inches tall. It tops out at a foot high, and this makes it a great choice for a container garden.

• Tall Double Mixed – This series gives you a great option to plant in your cutting garden, and it blooms in white, pink, and blue to form dried flower arrangements.

Cornflower Care

Cornflower is a very versatile plant that has several landscaping uses and uses inside of the home. You should consider adding it to your ornamental vegetable garden because the higher nectar content will attract pollinators to the space and boost your yield of squash, tomatoes, or any other plant that relies on them. You can add it to your wildflower garden to attract butterflies and bees. It also looks very nice in a cutting garden when you pair a blue cornflower with yellow marigolds or orange cosmos.

Like most annuals, you can buy this as a nursery start, but it’s also easy to grow from seed. You can grow it alongside more sturdy perennials, like coneflower or rudbeckia, and they’ll act like natural supports for the stems. You can stake your plant to keep it upright too.

Cornflower is a plant that blooms for roughly 10 weeks, starting in May and going until the middle of July. However, you can deadhead the spent flowers to increase the bloom time. Seeding your plants using a spaced-out schedule every two weeks to help extend the bloom time too. It makes a fabulous dried or cut flower, and you want to cut the blossoms in their prime before they wilt. To keep your cornflower looking as good as it can, the following guidelines can help.

Fertilizer

If your soil is very poor, you want to fertilize it once a month using compost tea or a diluted liquid manure. Start fertilizing this plant early in the spring when the plants are under six inches tall, and continue to do so throughout the summer. If you have more rich soil, you don’t need to fertilize them at all. Usually, mixing a bag or two of compost into the soil before you sow the seeds is enough to feed them for the whole season.

Light

Cornflowers prefer to be in full sun, but they can tolerate a small amount of shade in the afternoon. This is especially important during the hot days of summer. If they have shady conditions all day, this plant will grow leggy and it’s prone to flopping around.

Soil

This plant grows best in well-drained, rich soil that is on the alkaline side. The pH should range from 7.2 to 7.8. If your soil tends to be more acidic, you can add crushed limestone to the garden beds to fix it.

Temperature and Humidity

When you consider temperature, cornflowers will tolerate light freezes and very hot summer days. The plant thrives when the temperatures range between 60 and 80-degrees Fahrenheit. To reach flowering maturity, they need temperatures to range from 85 to 95-degrees Fahrenheit. The average humidity level for this plant ranges between 30% and 50%. You want to keep an eye on your garden during more humid days as this plant has issues with fungal diseases.

Water

Ideally, cornflower will need an inch of water every week. This is especially important during the hottest months in July and August. Let the soil dry out slightly between watering sessions, but don’t allow it to dry out 100% or the plant will start to flop. If this happens, watering it will usually perk it back up.

Cornflowers are a plant that readily self-seeds, so it’s easy to mix with a host of plants to get a full, colorful look.

How to Grow Cornflower From Seed

This plant self-seeds regularly when you plant it, so it’s very easy to propagate from seed. You can easily collect your own seeds from dried flower heads and store them through the winter until it’s time to plant them in the spring. Or, it’s also possible to buy inexpensive, large packs of seeds. If you want to grow it from seed, you can do the following:

• Sow the seeds in the late spring months directly into the garden after the last frost of the season recedes. Don’t worry about planting them too early as they won’t germinate until the frost threat passes.
• Cover the seeds with a ½-inch of soil and keep the seedbed well watered and moist until they start to germinate. This will happen usually within 10 days in warmer temperatures.
• Once the seeds sprout, you want to thin the seedlings to increase both the blooming and vigor in your plants.
• You can also start the seeds indoors to ensure they start to flower earlier. You want to do so six to eight weeks before the last frost date of the season using a seedling tray and a seed starter mix. We’ll go deeper into this propagation method below.

Starting Cornflower Indoors

Start by sowing your seeds inside roughly a month before you want to transition the seedlings outside. Some annual cornflower cultivars are day-length sensitive. So, they need roughly 14 hours of daylight to set their flower buds, so you might want to supplement natural sunlight exposure with grow lights to encourage earlier blooming. We suggest the following:

• Fill the individual peat pots, 3-inch diameter containers, or seed-starting flats with a high-quality seed starting mix. Moisten the mix and allow it to drain.
• In the filled flats, sow your seeds in rows. You’ll want to put three to four seeds per pot and cover them with a ½ inch layer of the soil because cornflowers require darkness to germinate. Spritz the mix with water to moisten it.
• Cover the containers with a clear plastic to keep the mix moist while your seeds germinate, and put the whole setup in a warm location between 60-degrees F and 70-degrees F.
• Remove the plastic covers when the seedlings emerge and put the pots in a sunny space or under your grow lights. Water as necessary to keep the soil mix moist but not soggy.
• Fertilize your seedlings once while they grow indoors using a liquid fertilizer.
• Transplant your cornflowers into the garden before they get four inches tall or taller.

It’s easy to start cornflowers from seed a month before you transplant them, and they readily self-seed, so they’ll come back the next year too.

Pruning Cornflower

While pruning isn’t necessarily necessary, pruning your plants can help extend how long they bloom in the summer. To do so, you’ll want to trim the longer stems back to the secondary stems once the first flowering period passes, and this is 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 the space to allow for late-season planting.

Potting and Repotting Cornflower

When you’re growing your cornflowers in containers or pots, you want to keep the soil on the dry side to help mimic pasture conditions. Terracotta pots or porous clay are best. Pick out a well-draining soil with perlite, or you can use a soilless potting medium using organic material that is very similar to a cactus soil. Deadhead your potted plants to get a tidy look, and be prepared for a shorter flowering season.

Garden Uses for Cornflower

One person’s favorite bright blue flower could just be someone else’s least favorite weed. So, if you decide to put cornflower in your garden, start very small. You’ll get a very good opportunity to get a feel for this plant and the vigorous growth habit by starting out with a container that is at least 24 inches in diameter and 12 inches deep. Put the pot away from any fertile ground to stop it from self-sowing, and deadhead any spent blooms before they get a chance to go to seed.

You might also choose to dedicate a planting space and deadhead the plant throughout the growing season to get controlled garden growing. If you have the space and want it to naturalize, you can easily put it in drifts, cutting gardens, mixed beds, meadows, and borders. Since this plant doesn’t need a lot of water once it establishes itself, it’s popular for xeriscaping.

To get a mixed bed with plants that have similar care needs, consider adding black-eyed susans, bee balm, daisies, phlox, snapdragons, and coneflower. This is a great flower to help you attract a range of pollinators like bees, and it also attracts hummingbirds, beneficial insects, butterflies, seed-foraging birds, and moths.

Cornflower Medicinal Properties

Back in Ancient Greece, it is rumored that the powerful healing properties of this plant helped to save Chiron the Centaur when he was shot with a poisoned arrow by Hercules. This plant has a long history of use for various medicinal properties. In folk medicine, it’s been used to help treat digestive issues, gynecological conditions, and skin issues.

This plant is a powerful analgesic and anti-inflammatory. Also, it has value as being an antifungal, anti-ulcerogenic, and anti-bacterial. Cornflower tea is rumored to help reduce chest congestion, fever, and water retention.

Cornflower Culinary Uses

Since they are edible, you can use your harvested cornflowers in the kitchen. The spicy and sweet flavor they offer falls somewhere between black pepper and cloves, and it has field green undertones. It’s important that you wash all of your flowers thoroughly before you eat them.

Adding fresh flower heads to a dinner plate or serving platter gives you a very elegant look and feel. All you have to do is snip the flower heads off just before you need them. Those that aren’t fully open are the best choice. You can also separate individual petals and sprinkle them over your cold dishes. You can also use the fresh-dried petals and brew them like tea or add them to sachet blends or potpourri.

There are both culinary and medicinal uses for cornflower, and this is what makes this plant so desirable with a host of gardeners.

Common Disease Problems

There are a few common disease problems that seem to crop up again and again with the cornflower. Knowing what they are will help you treat or prevent them to keep all of your plants healthy.

Aster Yellows

Aster Yellows cause your plants to be stunted with excessive growth called witch’s brooms. The petals will turn green and become deformed as the disease progresses. This is a virus-like condition that spreads via leafhoppers. You want to remove any infected plants to control the leafhoppers, and it’s a good idea to remove the weeds in the area that serve as alternate hosts to this disease.

Damping Off

This is one of the most common issues you end up with when you start your plants from seed. The seedling emerges from the soil and it looks healthy, but it suddenly wilts and dies for no apparent reason. Damping off is the result of a fungus that is active when there is too much moisture and the air temperatures go above 68-degrees F.

Generally speaking, this indicates that your soil is too wet or it has too much nitrogen fertilizer. You want to keep your seedlings moist but not overwater them, and make a point to not over-fertilize the seedlings. Think them out with a pair of sharp scissors to avoid overcrowding, and make sure there is good air circulation. If your plants are in containers, you want to disinfect them before and after you use them with a solution of 10% bleach and warm water.

Downy Mildew

This is a fungus that causes grayish-white patches to form on the undersides of the foliage first before spreading to both sides of the leaves. To avoid it, you should rotate your crops and avoid overwatering them. Make sure they have adequate air circulation through each growth stage and don’t overcrowd them. Don’t work around your plants when they’re wet.

Powdery Mildew

This is another fungal disease that appears on the top of your cornflower’s leaves when it’s humid. The leaves appear to have a gray or whitish coloration and they can curl. You can avoid this issue by giving your plants good air circulation by pruning and spacing them out.

Rust

There are several fungal diseases that cause rust-colored spots to appear on the plant stalks and foliage. You can practice crop rotation to avoid them, and remove any infected plants to prevent it from spreading.

Common Pests

There are several pests that love to wreak havoc on the cornflower if you don’t get rid of them as soon as you see them. They include but are not limited to:

Aphids

Red, black, green, or peach-colored sucking insects can easily spread disease as they feed on your plant’s leaves on the underside. They will leave a sticky residue on the foliage that draws ants in. However, aphids are only a problem if your cornflower is stressed out. You can attract or introduce natural predators into your garden to help battle aphids like ladybugs and wasps. You can also wash the plants with a strong spray from the hose or use an insecticidal soap.

Cutworms

As the name suggests, these insects cut the seedlings off at the soil level. To prevent it, put a paper cup collar around your plant’s base. You can also use a paper coffee cup with the bottom cut out. These insects are usually the biggest problem with younger seedlings. You can control them by controlling and handpicking weeds to take away the spot where they lay their eggs.

Leafhoppers

Leafhoppers can cause injury to your plant’s leaves and stunt their growth. They also quickly spread diseases from plant to plant. You’ll need to use insecticidal soaps and remove any affected plants to control them.

Spider Mites

These are very small spider-like pests that are roughly the size of a grain of pepper. They can be black, red, yellow, or brown. They suck on the plant juices and pull the chlorophyll out while injecting toxins that cause dots to appear on your cornflower’s foliage. Webbing is often visible on your plant as they progress. They will cause the foliage to turn yellow and become stippled and dry. They thrive in dry conditions and multiply rapidly. You can control them with a forceful spray of the hose every other day. You can try insecticidal soap or hot pepper wax too.

Stalk Borer

The larvae of this insect tend to tunnel up and down inside of your cornflower’s stems inside of the plant and cause them to wilt. By the time your plants start to wilt, it’s too late to save them. The larvae are roughly 1.5-inches long and a brownish gray with one dorsal stripe with two lateral stripes on either side. The lateral stripes on the front half get interrupted and the lower brown strips extend forward onto the side of the larvae head. The eggs start to hatch in May or June, and the moths lay them the previous September or October. You want to remove and destroy all plant debris and any nearby weeds to help control them.

Bottom Line

Cornflower is one that many people mistakenly think are native to the United States as they seem to appear in fields and alongside country roads each spring. However, they’re actually not native to the US, but they have such a vigorous growth habit that many states now classify them as invasive. So, check with your local agricultural office before you plant them and be prepared to keep them in check. If you do, you’ll get a mass of pretty blue flowers each summer.