Ornamental · Asteraceae
Cornflower
Centaurea cyanus
Scatter a little seed in full sun and lean soil, and cornflower will reward you with true-blue blooms all summer long.
Full sun
Every 7–14 days
USDA 2–11
1–3 ft · 0.3–0.9 m
Overview
Cornflower, which you may also know as bachelor's button, is a cool-season hardy annual in the daisy family, and it has cheered cottage gardens and grain fields for hundreds of years. Its true blue flowers are a color few other plants can offer, and the petals are edible with a mild, spicy-sweet taste. Best of all for a nervous beginner, it asks for almost nothing beyond a patch of sun and some open ground.
If you have ever worried you lack a green thumb, this is the flower to put your mind at ease. It shrugs off poor, dry soil that would defeat fussier plants, takes cold down to USDA zone 2, and reseeds itself so freely that a single packet often becomes a yearly fixture. Give it a little room and it forms a loose, airy clump from 1 to 3 feet tall.
The one thing to keep in mind is that it tends to sprawl in shade or rich ground, and that is easy to avoid. Plant it where the sun is strong and the soil stays lean, and you will see the stems stand straighter and the blue grow deeper. Deadhead the spent flowers and it keeps blooming for weeks, so a small mistake is always easy to put right.
Care
The short version: give cornflower full sun and average, well-drained soil on the lean side. Water when the top half of the soil dries out, skip the fertilizer, and snip off spent blooms to keep the flowers coming, and you really cannot go far wrong.
Light
Cornflower is happiest in full sun, a good 6 or more hours a day. It will put up with a little light shade, but a plant given too much shade tends to stretch, lean, and flop rather than stand tall, so brighter is always better.
Water
While it is settling in, give it medium, even moisture, letting the top half of the soil dry between waterings, which usually works out to about every 7 to 14 days. Once it is established, it shrugs off drought and low water with ease. The one thing it really dislikes is wet, soggy ground.
Soil
Average, well-drained loam is all it needs, and here is the reassuring part: this is a plant that genuinely thrives in poor soil. It is happy across a wide pH range from 6.0 to 8.0, so most garden beds will suit it with no special preparation at all.
Humidity
Ordinary outdoor air suits cornflower just fine, so there is no number for you to chase. What matters more is good airflow, since crowded, still conditions are what invite the rots and rusts that can trouble this plant.
Feeding
Cornflower needs little to no feeding, and it often does best with none at all, which is one less thing to fuss over. If you feel you must, a light balanced fertilizer at planting is all it wants, since rich ground only grows weak, floppy stems.
Pruning
Deadhead the spent flowers to keep new blooms coming and to gently rein in this plant's eager self-seeding. If a clump turns leggy partway through the season, cut it back without hesitation and it will often push out a fresh flush of growth.
Size & spacing
Plants reach 1 to 3 feet (30 to 91 cm) tall and spread 12 to 24 inches (30 to 61 cm) wide. Give each one that much room so air can move freely and the stems can lean on their neighbors for a little support.
When to plant
Cornflower loves a cool start, so there is no rush and no pressure here. Sow it indoors 6 to 8 weeks before your last spring frost, or simply scatter seed straight into the ground around that frost date. In mild-winter regions a fall sowing earns you earlier blooms, which arrive from late spring into summer, roughly May to July.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 6 to 8 weeks before the last spring frost
- Plant: Direct sow at the last spring frost date, or in fall in mild-winter climates
- Harvest: Blooms late spring into summer, roughly May to July
Hardiness
USDA hardiness zones: 2–11
Temperature: down to -46°C
Troubleshooting
Cornflower rarely causes much trouble, and the few problems it does have are easy to read and easy to mend. Floppy stems usually mean too little sun, sticky leaves tell you pests have moved in, and wilting almost always traces back to wet feet. Find what matches what you are seeing below, step in early, and you will be fine.
A wilting plant, soft stems, or rusty marks on the leaves
When a plant droops even though the soil is still damp, or its base goes soft and mushy, the cause is usually root and stem rot taking hold in soggy ground. Orange specks on the leaves point to rust instead. A badly rotted plant cannot be saved, and that is alright: pull it out, sort out the drainage, and keep water off the leaves so the rest of the patch stays healthy.
Fix:
- Improve soil drainage
- Avoid overhead watering and overwatering
- Remove and discard affected plants
When the stems lean and the plant starts to sprawl
If your cornflower is leaning and sprawling, the most likely reason is simply not enough light, so a plant set in shade or hemmed in by neighbors will lean while one in open sun holds itself upright. Ground that is too rich or too wet adds to it by pushing soft, weak stems. The good news is the fix is gentle: move it into the sun, go easy on feeding, and tuck a few twiggy stakes around the taller stems for a little help.
Fix:
- Grow in full sun
- Provide light support or grow-through staking for tall plants
- Avoid over-fertilizing
Sticky leaves and tiny bugs gathering on the stems
Little clusters of soft bugs along the stems and under the leaves usually mean aphids have found your plant, and mealybugs sometimes turn up alongside them. They leave a sticky film of honeydew and curl up the tender new growth, but this is an easy one to handle. Rinse them off with a firm spray of water, turn to insecticidal soap if a few cling on, and let the ladybugs finish the job for you.
Fix:
- Spray plants with a strong jet of water to dislodge pests
- Apply insecticidal soap if infestation is heavy
- Encourage natural predators such as ladybugs
Toxicity
There is truly nothing to worry about here. Cornflower is listed as non-toxic to pets, livestock, and people, and the petals are even edible with a gentle spicy-sweet flavor. You can plant it freely around cats, dogs, horses, and curious children, and rest easy.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
You can relax with a cat nearby, since cornflower holds no toxic compounds and a curious nibble of leaf or flower will do no harm.
Dogs None
A dog can brush past the plant or chew on it without any worry, because there is nothing poisonous in cornflower at all.
Horses None
Cornflower is listed as non-toxic to horses, so even a grazing mouthful is nothing to fret about.
Rabbits Safe
Rabbits are welcome to the leaves and petals as they please, because the plant carries no toxins to trouble them.
Livestock Safe
Cattle, goats, and sheep grazing in a pasture face no danger from cornflower whatsoever.
Birds Safe
The seeds and flowers are perfectly safe for birds, and you will often spot finches picking happily at the spent heads.
People Safe
The petals are edible and carry a gentle spicy-sweet taste, so feel free to scatter them over a salad or float them in a cup of tea.
Varieties
Cornflower offers more than the famous blue, and any of these is a lovely place to begin. Here are the color forms you are most likely to come across.
Blue cornflower
This is the classic that gives the plant its name, opening deep blue double buttons you will recognize at once.
Pink and lavender forms
Gentle selections that trade the usual blue for soft pink, lavender, or purple blooms.
White cornflower
A pure white form that quietly softens a planting or helps round out a mixed-color patch.
How to propagate
Few flowers are kinder to grow from seed than cornflower, and it cheerfully sows the next generation for you, so it almost takes care of itself.
SeedEasy
Start indoors 6 to 8 weeks before the last frost, or direct sow at the last spring frost; fall sowing works in mild-winter climates · Germinates and establishes within a few weeks; reseeds readily in the garden
Cornflower is a cool-season hardy annual, and growing it straight from seed could not be more forgiving for a first try. Start it indoors 6 to 8 weeks before the last frost, or simply scatter seed in the ground at the last frost date, and a fall sowing works nicely in mild-winter areas too. It comes up and settles in within a few weeks, then reseeds itself freely, so it often returns on its own the following year with no effort from you.
Myths
Cornflower is poisonous to pets like cats and dogs.
You can set this worry down, because Centaurea cyanus is listed as non-toxic to cats, dogs, and horses, and the petals are edible for people too. There is simply no toxin here to fear, so a curious nibble from a pet or a small child is nothing to lose sleep over.
All Centaurea are noxious invasive weeds that should never be planted.
A handful of relatives like knapweed and star thistle do run wild, but the annual ornamental cornflower is a gentle, easygoing garden flower. Snip off the spent blooms and you keep its self-seeding comfortably in check.