Growing and Caring for Cornflowers (Centaurea cyanus) from Seed

Cornflowers, with their sky-blue blooms and cottage garden charm, are a delight in any Cornish border. They thrive in the wilder corners of a garden, weaving between other plants or adding height and colour to a cut flower patch. Though simple to grow, a little attention to detail when sowing and caring for them will reward you with a summer-long display.

Starting Cornflowers from Seed

When to Sow:

• Indoors: Start 4–6 weeks before the last frost (typically March–April).
• Outdoors: Direct sow from mid-April, after the risk of frost.

How to Sow Indoors:

• Fill seed trays or small pots with moist, fine seed compost.
• Sow seeds on the surface, covering lightly with 0.5–1 cm of compost or vermiculite — a little darkness helps germination.
• Cover with a plastic lid or bag until germination (7–14 days at 15–20°C).
• Once seedlings emerge, remove cover and place in bright light.

Growing On:

• When seedlings have two true leaves, prick out into larger pots.
• Grow in a bright, cool place.
• Harden off gradually before planting outside.

Planting Out and Care

Cornflowers love a sunny spot with free-draining soil. They perform well in poorer soils and can bring a touch of relaxed beauty to less cultivated areas.

• Space plants 10–15 cm apart.
• Water young plants well until established.
• Avoid rich feeding — this encourages foliage over flowers.
• Regular deadheading keeps blooms coming.
• Stake taller types in exposed spots.

Optimising Soil for Cornflowers

Choose a sunny site with well-drained, moderately fertile soil.

• Light, sandy, or loamy soils work best.
• Improve heavy soils with sand, gravel, or compost.
• Avoid overfeeding — too rich and you’ll get leaves, not flowers.
• Maintain a neutral to slightly alkaline pH (6.5–7.5).
• Prepare a fine tilth before sowing.

Protecting Young Plants

• Birds: Netting helps protect emerging seedlings.
• Slugs and Snails: Hand-pick, use barriers, or organic slug pellets.

Annual vs Perennial Cornflowers

Annuals (Centaurea cyanus):

• Quick bloomers — often within 10–12 weeks.
• Thrive in poorer soils.
• Need regular deadheading.
• Self-seed if left unchecked.

Perennials (Centaurea montana):

• Return each year from the root.
• Prefer slightly richer soil and regular mulching.
• Benefit from dividing every few years.
• May require staking and deadheading.

Quick Care Reminders

With thoughtful care, cornflowers bring a generous sweep of colour to Cornish gardens — perfect for informal borders, cutting patches, or even meadow-style planting. Their mix of ease, beauty, and tradition makes them a cherished choice for gardeners looking for low-fuss, high-reward blooms.