Cornflower
Centaurea cyanusUSDA | Grow Zone
3-10Outdoors all year in zones 3 to 10. Anywhere colder, keep it as a houseplant. Protect it below 32°F.
- Light
- Full sun, 6-8 hours
- Water
- When top 1 in is dry
- Humidity
- 40-60%
- Temperature
- 60-75°F (15-24°C)
- Difficulty
- Beginner
- Growth
- Moderate
- Mature size
- 2-3 ft tall, 1-2 ft wide
- Pets
- Non-toxic to pets
Cornflower, or Centaurea cyanus, is a charming annual known for its vibrant blue flowers and easy care. Native to Europe, it adds a splash of color to gardens and is often used in wildflower mixes.
Ask Vesper about Cornflower
Ideal temperature
60-75°F is where it grows fastest. Below 32°F cold damage starts.
Spacing and harvest
- Mature size
- 2-3 ft tall, 1-2 ft wide
- Plant apart
- 12-24 in
- Frost
- Half hardy: light frost only
Everything it needs
9 essentials at a glance
Watering
Cornflowers prefer well-drained soil and should be watered deeply but infrequently.
Water them once the top inch of soil feels dry, typically every 1-2 weeks depending on weather conditions. In hot, dry spells, you may need to water more frequently. Signs of over-watering include yellowing leaves and root rot, while under-watering can cause wilting and browning of leaf edges.
Light
Cornflowers thrive in full sun, requiring at least 6-8 hours of direct sunlight daily.
They prefer bright, sunny locations in the garden, as insufficient light can lead to leggy growth and fewer blooms. They can tolerate partial shade but will produce fewer flowers.
Soil
The ideal soil for cornflowers is well-drained, sandy or loamy soil with a pH range of 6.0 to 7.0.
They do not tolerate heavy clay soils well, which can lead to root rot. A recommended potting mix includes a combination of potting soil, sand, and perlite to enhance drainage.
Humidity
Cornflowers prefer moderate humidity levels, ideally around 40-60%.
To increase humidity, you can mist the plants or place a tray of water nearby. Signs of low humidity stress include browning leaf tips and wilting flowers.
Temperature
Cornflowers thrive in cooler temperatures, ideally between 60-75°F (15-24°C).
They are hardy in USDA zones 3-10, tolerating light frost but not extreme heat. During hot summer months, they may require some shade to prevent heat stress.
Fertilizing
Use a balanced fertilizer with an NPK ratio of 10-10-10 or similar.
Fertilize every 4-6 weeks during the growing season, starting in spring. Signs of nutrient deficiency include pale leaves and poor flowering, which can be remedied by applying fertilizer.
Pruning
Prune cornflowers after the blooming period to encourage a second flush of flowers.
Use clean, sharp scissors or pruning shears to cut back spent blooms and any dead or damaged foliage. Deadheading spent flowers can also promote more blooms throughout the season.
Repotting
Cornflowers generally do not require frequent repotting, but if grown in containers, consider repotting every 1-2 years or when roots outgrow the pot.
Signs that repotting is needed include roots growing out of the drainage holes and stunted growth. When repotting, choose a pot 1-2 inches larger in diameter and refresh the soil.
Propagation
Cornflowers can be propagated through seeds or division.
For seed propagation, sow seeds directly in the garden in early spring or fall. Space seeds about 12 inches apart and cover lightly with soil. For division, dig up established plants in early spring or fall and separate them into smaller clumps, replanting immediately.
When it's unhappy
Yellow leaves
Why it happens
This can be caused by over-watering or nutrient deficiency.
How to fix it
Ensure proper watering practices and consider fertilizing if nutrient deficiency is suspected.
Root rot
Why it happens
Over-watering and poor drainage can lead to root rot.
How to fix it
Allow the soil to dry out between waterings and ensure pots have adequate drainage holes.
Leggy growth
Why it happens
Insufficient sunlight can cause plants to stretch towards the light.
How to fix it
Move the plant to a sunnier location to encourage bushier growth.
Pest infestations (aphids, spider mites)
Why it happens
Pests can thrive in warm, dry conditions.
How to fix it
Inspect plants regularly and treat infestations with insecticidal soap or neem oil.
Poor flowering
Why it happens
This can result from insufficient light or nutrient deficiency.
How to fix it
Ensure the plant receives full sun and consider fertilizing to promote blooming.
Care through the year
Spring
In spring, sow seeds directly in the garden after the last frost. Ensure they receive full sun and water regularly as they establish.
Summer
During summer, monitor for pests and water as needed. Deadhead spent flowers to encourage continued blooming.
Fall
In fall, allow the plants to go to seed if you want them to self-seed for next year. Cut back any dead foliage after the first frost.
Winter
In winter, if grown in pots, protect them from extreme cold by moving them to a sheltered location. Mulch garden beds to protect roots.
Toxicity & Safety
Cornflowers are generally non-toxic to pets and children. However, ingestion of large quantities may cause mild gastrointestinal upset. The plant is safe to grow around cats and dogs.
Good to know
How often should I water my cornflower?
Water cornflowers when the top inch of soil feels dry, typically every 1-2 weeks. Adjust frequency based on weather conditions.
Why are my cornflower leaves turning yellow?
Yellow leaves can indicate over-watering or a nutrient deficiency. Check your watering schedule and consider fertilizing.
Can I grow cornflowers in pots?
Yes, cornflowers can be grown in pots. Ensure the pot has good drainage and use a well-draining potting mix.
When do cornflowers bloom?
Cornflowers typically bloom from late spring to early summer, with the possibility of a second bloom in late summer if deadheaded.
What is the best soil for cornflowers?
Cornflowers prefer well-drained, sandy or loamy soil with a pH of 6.0 to 7.0 for optimal growth.
Are cornflowers annual or perennial?
Cornflowers are typically grown as annuals, but they can self-seed and return in subsequent years.
How do I propagate cornflowers?
Cornflowers can be propagated from seeds sown directly in the garden or by dividing established plants in spring or fall.
Track this plant in your garden.
Set care reminders, log growth, and join a community of plant lovers.