How to Grow Cornflower
Centaurea cyanus
Cornflowers are hardy annuals suited to full sun and well-drained, even poor, soil. Direct sow in spring or autumn for early displays. Plants are upright and may need light staking in windy sites. Deadhead to keep a long flowering season, or leave some seed heads to self-sow. Great for cutting—pick when the first few florets open. Avoid overfeeding; lush growth flops and flowers less.
When to Start
Direct sow outdoors as soon as soil reaches 5°C — typically early to mid spring. Can also be started indoors 4 weeks earlier for a head start.
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Growth Stages
Approximate days from start
Care Essentials
- Rarely needed. Thrives in poor soil — rich soil produces floppy growth.
- Classic wildflower meadow plant. Self-seeds freely. Blue varieties are the most popular.
Growing Conditions
- Min. soil temperature
- 5°C+
- Germination temperature
- 15–20°C
Pet Safety
- Sow indoors
- —
- Transplant out
- —
- First harvest
- —
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Spacing & Planting
| Plant spacing | 20 cm |
| Row spacing | 30 cm |
| Sow depth | 0.5 cm |
| Mature height | 75 cm |
| Mature spread | 30 cm |
Also known as Bachelor's Button. Can be direct-sown and thinned. Closer spacing can provide some mutual support for tall stems.
Pests & Diseases
Pest Aphids
Identification: Clusters of small green insects on shoot tips and flower buds, causing distorted growth and sticky honeydew
- Blast off with a strong jet of water
- Spray with fatty acid-based insecticide
- Encourage ladybirds, lacewings and hoverflies
- Spray with a contact insecticide containing deltamethrin or lambda-cyhalothrin
Pest Slugs and Snails
Identification: Irregular holes in young leaves and slime trails around plants, worst in wet weather
- Use beer traps or copper tape barriers
- Apply organic slug pellets (ferric phosphate)
- Encourage natural predators such as hedgehogs and ground beetles
- Ferric phosphate-based pellets
Disease Powdery Mildew
Symptoms: White powdery coating on leaves and stems, causing yellowing and reduced vigour
Treatment: Remove badly affected leaves. Spray with a fungicide if severe
Prevention: Space plants well for good airflow, avoid overcrowding, and thin seedlings early
Disease Rust
Symptoms: Orange-brown raised pustules on the undersides of leaves, with corresponding yellow spots on upper surfaces
Treatment: Remove and destroy affected leaves. Improve air circulation around plants
Prevention: Avoid overhead watering, space plants adequately, and remove plant debris at the end of the season
Growing Conditions
| Min. soil temperature | 5°C |
| Germination temperature | 15–20°C |
| Base growth temperature | 4°C |
| Min. daylength to start | 9h |
| Photoperiod sensitivity | day neutral |
Frequently Asked Questions
- How far apart should I plant Cornflower?
- Plant Cornflower 20cm apart with 30cm between rows.
- When does Cornflower flower?
- Cornflower typically flowers approximately 60 days after transplanting.
- Is Cornflower frost hardy?
- Cornflower is classified as Hardy.
