Perennial cornflower

Sun

Full sun to light partial shade; afternoon shade helps in warmer gardens.

Water

Water regularly while establishing. Established plants tolerate short dry spells, but flower best with some moisture; avoid persistently wet soil.

Soil

Well-drained, moderately fertile soil, from slightly acidic to alkaline. Avoid waterlogged clay and heavily enriched beds.

Height

1-2 ft (0.3-0.6 m)

Spread

1-2 ft (0.3-0.6 m), eventually wider if allowed to spread

Flowers

Late spring to early summer, with fringed violet-blue outer florets and reddish-purple centres; a smaller repeat flush may follow cutting back.

Foliage

Soft, slightly hairy, grey-green leaves, lance-shaped to oblong, on leafy stems.

Growth

Moderate to fast

Care needed

Medium

• Pollinators
• Cold hardy
• Wildlife
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Easy

Toughness

Very tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   1.2 ft (0.36 m)

3. After 2 years

   1.4 ft (0.42 m)

4. After 3 years

   1.5 ft (0.45 m)

   full size

About 2 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Native to

the UK

Invasive in

the US and Canada

In the garden

Spreads vigorously: plan to contain it.

Growth rate

Fast

• Water newly planted clumps during dry weather until roots are established.
• Apply a thin compost mulch in spring, keeping it away from the crown; routine feeding is rarely needed.
• Avoid rich fertiliser and excessive watering, which encourage floppy growth.
• Divide crowded clumps every 3-4 years in spring or early autumn.
• Remove unwanted shoots and seedlings promptly, especially near natural areas.

Pruning. Remove spent flower heads before seed ripens. After the main flowering flush, cut tired stems and foliage back to about 4-6 in (10-15 cm) above the ground to encourage fresh growth and possible repeat flowering.

Early spring

Remove dead stems and check for shoots spreading beyond the planting area.

Spring

Plant or divide clumps, water them in, and apply a thin compost mulch.

Late spring

Deadhead fading flowers regularly to limit self-seeding.

Early summer

Cut back after the main flowering flush and water if the soil is dry.

Late summer

Remove unwanted seedlings and check foliage for mildew.

Autumn

Divide overgrown clumps where winters are mild enough for roots to establish; otherwise wait until spring.

• Plant in small groups toward the front or middle of cottage borders, alongside hardy geraniums and lady's mantle.
• Combine with catmint and salvias for a loose blue-and-purple planting in a sunny border.
• Use beside pale pink peonies or roses, where its blue flowers provide a cool contrast.
• Plant along a sunny woodland edge with good drainage, leaving access to control spreading clumps.

Garden styles it suits: Cottage garden, English country, Blues and silvers, Pollinator garden, Modern rustic and Traditional.

Plant it with: Hardy geranium, Lady's mantle, Catmint, Meadow sage, Peony and Bearded iris.

Wildlife: The flowers provide nectar and pollen for bees and attract butterflies and other flower-visiting insects.

• Powdery mildew: improve airflow, avoid drought stress, and cut back badly affected foliage after flowering.
• Root or crown rot in wet soil: improve drainage or move the plant to a raised position; discard badly rotted plants.
• Flopping stems: reduce feeding, provide more sun, and use discreet supports if needed.
• Unwanted spread: deadhead before seed develops, remove seedlings, and dig out encroaching underground stems.

Not known to be toxic to people, cats, dogs or horses. No particular part is established as poisonous, but species-specific safety information is limited; do not treat it as an edible plant or livestock feed.

Where it spreads. Can spread aggressively by underground stems and seed. It is reported as invasive in parts of the Pacific Northwest, including Washington State and British Columbia; check local guidance before planting and keep it away from natural habitats.

• Annual cornflower (Centaurea cyanus)

  An annual with narrower leaves and more slender, branching stems; mountain bluet has broader leaves and forms a persistent spreading clump.

• Persian cornflower (Centaurea dealbata)

  Usually has pink flowers with pale centres and deeply divided leaves with whitish undersides, rather than blue flowers and mostly undivided leaves.

The epithet montana means 'of mountains', reflecting the species' European mountain habitats, while perennial cornflower distinguishes it from the annual cornflower.

Propagation. Divide clumps in spring or early autumn, keeping roots and healthy shoots on each piece. The species can also be raised from seed, but seedlings of named cultivars may differ from the parent.

Accepted botanical name

Centaurea montana

In the US and Canada

Introduced in Alaska, Canada, the lower 48 states and St. Pierre and Miquelon.

Native range

Austria, Baltic States, Belgium, Czechoslovakia, France, Germany, Great Britain, Ireland, Italy, Netherlands, Northwest European R and Norway.

Measured

Average height 45 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.