Centaurea cyanus 'Blue Ball' (d)

RHS Plant Profile
cornflower 'Blue Ball'

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Synonyms

Centaurea cyanus 'Double Blue'

Plants for pollinators
Annual Biennial
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An annual cornflower, to around 80cm high in flower, with lance-shaped, grey-green leaves. Double, showy bright cobalt blue flower-heads are produced all through the summer

Position

Full sun

Soil Types

Chalk, Loam, Sand

Size

Time to Maturity
1–2 years

Growing Conditions

Chalk Loam Sand
Moisture
Moist but well–drained or Well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
South–facing or West–facing
Exposure
Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

  • H1A: under glass all year (>15C)
  • H1B: can be grown outside in the summer (10 - 15)
  • H1C: can be grown outside in the summer (5 - 10)
  • H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
  • H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
  • H4: hardy through most of the UK (-10 to -5)
  • H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
  • H6: hardy in all of UK and northern Europe (-20 to -15)
  • H7: hardy in the severest European continental climates (< -20)
H6

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Clump forming
Genus
Centaurea may be annuals, perennials or subshrubs, with simple or pinnately lobed leaves and showy thistle-like flowers-heads, often with enlarged outer florets
Name Status
Unresolved

How to Grow

Cultivation

Grow in well-drained soil in full sun

Propagation

Propagate by seed sown in-situ in spring or autumn

Suggested planting locations and garden types

  • Cottage and informal garden
  • Patio and container plants
  • Wildflower meadow
  • Wildlife gardens
  • Cut flowers
  • Flower borders and beds

Pruning

Deadhead regularly to prolong flowering

Pests

Generally pest-free

Diseases

May be susceptible to powdery mildews