Ornamental · Asteraceae
Cornflower
Centaurea cyanus
Scatter the seed in full sun and lean soil, and cornflower rewards you with true-blue blooms all summer.
Full sun
Every 7–14 days
USDA 2–11
1–3 ft · 0.3–0.9 m
Overview
Cornflower, also called bachelor's button, is a cool-season hardy annual in the daisy family that has grown in cottage gardens and grain fields for centuries. Its true blue flowers are hard to match in any other plant, and the petals are edible with a mild, spicy-sweet taste. It asks for almost nothing beyond sun and a patch of open ground.
This is one of the easiest flowers a beginner can grow. It shrugs off poor, dry soil that would starve fussier plants, handles cold down to USDA zone 2, and reseeds itself so freely that one packet often becomes a yearly fixture. Give it room and it forms a loose, airy clump from 1 to 3 feet tall.
The trade-off for that toughness is a tendency to sprawl in shade or rich ground. Plant it where the sun is strong and the soil stays lean, and the stems stand straighter and the blue runs deeper. Deadhead the spent flowers and it keeps blooming for weeks instead of rushing to set seed.
Care
The short version: full sun and average, well-drained soil that runs on the lean side. Water when the top half dries out, skip the fertilizer, and snip off spent blooms to keep the flowers coming.
Light
Cornflower wants full sun, a good 6 or more hours a day. It will tolerate a little light shade, but plants grown in too much shade stretch, lean, and flop instead of standing tall.
Water
Give it medium, even moisture while it is getting established, letting the top half of the soil dry between waterings, which works out to roughly every 7 to 14 days. Once settled in, it shrugs off drought and low water. The one thing it hates is wet, soggy ground.
Soil
Average, well-drained loam is plenty, and this is a plant that genuinely thrives in poor soil. It adapts to a wide pH range from 6.0 to 8.0, so most garden beds will do without any special prep.
Humidity
Ordinary outdoor air suits it fine, so there is no number to chase. What matters more is good airflow, since crowded, still conditions invite the rots and rusts that trouble this plant.
Feeding
Cornflower needs little to no feeding and often does best with none at all. If you feel the urge, 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 the blooms coming and to rein in this plant's eager self-seeding. If a clump turns leggy partway through the season, cut it back and it often pushes out a fresh flush.
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 moves freely and the stems have support from their neighbors.
When to plant
Cornflower likes to start in cool weather. Sow it indoors 6 to 8 weeks before your last spring frost, or scatter seed straight into the ground around that frost date. In mild-winter regions a fall sowing gives 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 gives much trouble, and the few issues it does have are easy to read. Floppy stems point to too little sun, sticky leaves mean pests have moved in, and wilting usually traces back to wet feet. Match what you see below and act early.
Wilting plants, mushy stems, or rusty leaf spots
When a plant wilts even though the soil is damp, or its base turns soft and mushy, root and stem rot in wet ground is usually to blame. Orange pustules on the leaves point to rust instead. There is no fixing badly rotted plants, so pull them, fix the drainage, and keep water off the foliage.
Fix:
- Improve soil drainage
- Avoid overhead watering and overwatering
- Remove and discard affected plants
Stems flop over and the plant sprawls
Floppy cornflowers almost always come down to too little light, so a plant tucked into shade or a crowded bed leans and sprawls while one in full sun stands tall. Rich or soggy ground makes it worse by pushing soft, weak growth. Move it into the sun, ease off the feeding, and slip a few twiggy stakes around tall stems to hold them up.
Fix:
- Grow in full sun
- Provide light support or grow-through staking for tall plants
- Avoid over-fertilizing
Sticky leaves crawling with tiny insects
Clusters of soft little bugs on the stems and the undersides of leaves point to aphids, with mealybugs sometimes joining in. They leave behind a sticky honeydew and twist the fresh new growth. Blast them off with a hard jet of water, reach for insecticidal soap if they hang on, and let ladybugs do the rest.
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 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.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe around cats, with no toxic compounds to worry about if one nibbles a leaf or flower.
Dogs None
Dogs can brush past or chew on cornflower without harm. There is nothing poisonous in the plant.
Horses None
Listed as non-toxic to horses, so a grazing mouthful is no cause for alarm.
Rabbits Safe
Rabbits can eat the leaves and petals freely, since the plant carries no toxins.
Livestock Safe
Grazing cattle, goats, and sheep face no risk from cornflower in the pasture.
Birds Safe
The seeds and flowers are safe for birds, and finches often pick at the spent heads.
People Safe
The petals are edible, with a mild spicy-sweet flavor, and they brighten salads or a cup of tea.
Varieties
Cornflower comes in more than the famous blue. These are the color forms you are most likely to find.
Blue cornflower
The classic form, with intense blue double buttons that give the plant its name.
Pink and lavender forms
Selections that bloom in pink, lavender, or purple instead of the usual blue.
White cornflower
A pure white form that softens a planting or fills out a mixed-color patch.
How to propagate
Cornflower is about as easy to grow from seed as a flower gets, and it happily sows the next generation for you.
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 that grows best straight from seed. Start it indoors 6 to 8 weeks before the last frost or scatter seed in the ground at the last frost date, and in mild-winter areas a fall sowing works too. It comes up and settles in within a few weeks, then reseeds itself freely to come back on its own next year.
Myths
Cornflower is poisonous to pets like cats and dogs.
Centaurea cyanus is listed as non-toxic to cats, dogs, and horses, and its petals are edible for people too. There is no toxin here to fear, so a curious nibble from a pet or a child is nothing to lose sleep over.
All Centaurea are noxious invasive weeds that should never be planted.
A few relatives like knapweed and star thistle do run wild, but the annual ornamental cornflower is a tame, easy garden flower. Deadhead the spent blooms and you keep its self-seeding in check.