Inula Royleana
Midwest Gardening
Centaurea Cornflower

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Centaurea, a perennial cornflower with unusual flowers

The Centaurea genus of the daisy family includes several species such as annual cornflower and knapweed, Centaurea montana are the perennial cornflowers or Mountain Bluet.  They prefer full sun, but can bloom fairly well in light shade.  Centaurea reproduce quite easily from small pieces or root left behind in the soil after removal or division, and can spread quite rapidly.  This is a tough perennial that tolerates nearly any soil condition except consistently wet, and is not at all fussy about pH.  They are easy to grow, very tolerant of drought, and will naturalize.  The blooms are large, very showy, long blooming, and quite unique.

 

Centaurea montana ‘Amethyst in Snow’
Centauea montana 'Amethyst in Snow' by Sarah

  • Common Name:  Perennial Cornflower, Mountain Cornflower, Bachelor’s Button, Montana Knapweed, Mountain Bluet
  • Plant Type:  Herbaceous perennial
  • Height:  12-30”
  • Spread:  10-30”
  • Sun/Shade Requirements:  Full sun to light shade
  • Water Requirements:  Low to average, drought tolerant
  • Soil Requirements:  Average well drained soil
  • Growth Habit:  Erect, in low mounding clumps
  • Bloom Time: Mid May to Mid June, light rebloom in autumn if deadheaded.
  • Bloom Color: White petals with plum-purple center
  • Bloom Form:  2 1/2” showy flowers with spider-like, fringed petals, born singly on 12-18” stems.
  • Foliage:  Large, gray green lower leaves are 7” and lance shaped, diminishing in size progressing up the stalk.
  • Fragrance:  None
  • Pest and Disease Resistance:  In wet conditions may be susceptible to dieback and mildew.  Deer and rabbit resistant.
  • Fertilize:  Feeding not required, may be fertilized in early spring if soil is unusually poor.
  • Maintenance:  Divide in spring or fall every 2-3 years.
  • Other:  Attracts butterflies
  • Hardiness:  Zones 3-8

‘Amethyst in Snow’ may be the first bi-color cultivar of Centaurea montana that was introduced to the commercial market.  The striking blooms are snow white with plum-purple centers and black-edged bracts under the petals.  The ‘Purple Heart’ culitivar is believed to be identical to ‘Amethyst in Snow’.  Deadhead spent flowers to prevent self seeding and encourage rebloom.  In midsummer, the foliage may become less than attractive.  Cut the whole plant to the ground or back by two thirds, and fresh foliage will emerge.  Grow in full sun to prevent stems from becoming long and floppy.  ‘Amethyst in Snow’ can be expected to live 15 years or more.

Fertile soil and cool northern climates create a perfect growing environment, and ‘Amethyst in Snow’ may multiply rapidly.  Fertilizing may also encourage spread.  Regular division will help minimize the spread, but be sure to remove the entire root structure as remnants left behind will often produce new plants.  Wonderful for naturalizing or in a cottage garden.  An eye catching cut flower in a fresh or dried arrangement.

 

Centaurea montana ‘Montana Blue’
Centaurea Montana 'Blue' by TOG

  • Common Name:  Perennial Cornflower, Mountain Cornflower, Bachelor’s Button, Montana Knapweed, Mountain Bluet
  • Plant Type:  Herbaceous perennial
  • Height:  12-24”
  • Spread:  12-18”
  • Sun/Shade Requirements:  Full sun to part shade.
  • Water Requirements:  Low to average, drought tolerant
  • Soil Requirements:  Average well drained soil
  • Growth Habit:  Upright, low mounding clump, spreading
  • Bloom Time: May through June, light rebloom repeats if deadheaded
  • Bloom Color: Cornflower blue with purple-blue centers and black edged bracts.
  • Bloom Form:  2-3” showy flowers with spider-like, fringed petals, born singly on strong stems.
  • Foliage:  Large gray green lower leaves are 7” and lance shaped, diminishing in size progressing up the stalk.
  • Fragrance:  None
  • Pest and Disease Resistance:  In wet conditions may be susceptible to dieback and powdery mildew.  Deer and rabbit resistant.
  • Fertilize:  Feeding is not required, may be fertilized in early spring if soil is unusually poor.
  • Maintenance:  Divide in spring or fall every 2-3 years.
  • Other:  Attracts butterflies and bees
  • Hardiness:  Zones 2-8
Centaurea Montana 'Montana Blue' by TOG

This Centaurea has been found marketed under several different names, sometimes simply Centaura montana, but also with a cultivar name of ‘Blue’, ‘Montana Blue’, ‘Northern Lights’, as well as others.  It is native to the mountains of Europe, and so is very drought resistant.  Exactly why they also do very well in containers that may dry out quickly.
Centaurea montana 'Northern Lights' by TOG

‘Montana Blue’ has striking blooms of deep cornflower blue and purple-blue centers.  Deadhead spent flowers to prevent self seeding and encourage rebloom.  ‘Montana Blue’ spreads quite aggressively by underground rhizomes and by self seeding.  In midsummer, the foliage may become less than attractive.  Cut the whole plant to the ground, or back by two thirds, and fresh foliage will emerge.  Grow in full sun to prevent stems from becoming long and floppy.

Fertilie soil and cool northern climates create a perfect growing environment, and ‘Montana Blue’ may multiply rapidly.  Fertilizing may also encourage spread.  Regular division will help minimize the spread, but be srue to remove the entire root structure, as remnants left behind will often produce new plants.  ‘Montana Blue’ is perfect for naturalizing or in a cottage garden.  Striking in a fresh arrangement or dried.  Cut flowers will last 4 or 5 days.

 

Centauea montana ‘Alba’
Centaurea montana 'Alba' by rattyfied

  • Common Name:  Perennial Cornflower, Mountain Cornflower, Bachelor’s Button, Montana Knapweed, Mountain Bluet
  • Plant Type:  Herbaceous perennial
  • Height:  12-24”
  • Spread:  8-12”
  • Sun/Shade Requirements:  Full sun to part shade
  • Water Requirements:  Low to average, drought tolerant
  • Soil Requirements:  Average, well drained
  • Growth Habit:  Upright, clump florming
  • Bloom Time: May to July
  • Bloom Color: Pure white petals with violet centers.
  • Bloom Form:  2” showy flowers with spider-like, fringed petals, born singly on strong stems.
  • Foliage:  Large lower leaves are 7” and lance shaped, diminishing in size progressing up the stalk.
  • Fragrance:  None noted
  • Pest and Disease Resistance:  No notable problems.  Deer and rabbit resistant.
  • Fertilize:  Feeding is not required, may be fertilized in early spring if soil is unusually poor.
  • Maintenance:  Divide in spring or fall every 2-3 years.
  • Other:  Attracts butterflies and bees.  Salt tolerant.
  • Hardiness:  Zones 3-8

‘Alba’ has stunning pure white blooms, but often when grown from seed up to 25% of the blooms will be produced in varying shades of blue.  This only adds to the charm of the plant.  Early blooming is abundant, with occasional blooming throughout the season.  Deadhead or cut flowers for fresh arrangements to minimize self seeding.  ‘Alba’ reliably blooms in the first year.  This Centaurea is sometimes difficult to find.

If ‘Alba’s’ foliage becomes unattractive, it may be cut back to the ground.  Fresh foliage will emerge, and it may flower again.  Stems are short and strong enough to avoid staking.  ‘Alba’ is quite tolerant of a range of soils, but does prefer moist, but well drained soil with plenty of sun.  Do not over water, and avoid sites that may remain wet over winter.

‘Alba’ is an excellent perennial border plant if space to spread allows, in wildflower or naturalized garden, or in rock gardens.  It also works nicely as a taller groundcover, great on a hillside. It can spread somewhat aggressively by underground runners and self seeding.  Regular division and deadheading will help minimize spread.  With its’ drought tolerance and some resistance to salt, ‘Alba’ may work well in a roadside planting.

 

Centaurea montana ‘Purple Heart’
Centaurea montana 'Purple Heart' by jacki-dee

  • Common Name:  Perennial Cornflower, Mountain Cornflower, Bachelor’s Button, Montana Knapweed, Mountain Bluet
  • Plant Type:  Herbaceous perennial
  • Height:  18-32”
  • Spread:  12-24”
  • Sun/Shade Requirements:  Full sun to light shade.
  • Water Requirements:  Low to average, prefers consistently moist soil but is drought tolerant.
  • Soil Requirements:  Average well drained.
  • Growth Habit:  Upright in mounding clumps
  • Bloom Time: May into July, light reblooming if deadheaded.
  • Bloom Color: White petals with purple centers
  • Bloom Form:  2” showy flowers with spider-like, fringed petals, born singly on short strong stems.
  • Foliage:  Large lower leaves are 7” and lance shaped, diminishing in size progressing up the stalk.
  • Fragrance:  None
  • Pest and Disease Resistance:  In wet conditions may be susceptible to dieback and mildew.  Deer and rabbit resistant.
  • Fertilize:  Feeding not required, may be fertilized in early spring if soil is unusually poor.
  • Maintenance:  Divide in spring or fall every 2-3 years.
  • Other:  Attracts butterflies and bees.
  • Hardiness:  Zones 3-8

‘Purple Heart’ has pure white petals surrounding a dark purple center, creating an eye catching bloom.  It is very similar to ‘Amethyst in Snow’, in fact many believe it may be identical.  ‘Purple Heart’ is fairly drought tolerant, more so than ‘Gold Bullion’, however all the Centaurea montanas will bloom best if they do not dry out.  Fertile soil and cool northern climates create a perfect growing environment where ‘Purple Heart’ may multiply rapidly.  Fertilizing may also encourage the spread.  Regular division will help minimize the spread.  Root remnants left in the soil may produce new plants.

Deadhead ‘Purple Heart’s’ spent flowers to help prevent self seeding and encourage rebloom.  In midsummer if foliage becomes less than attractive, the plant may be cut back by two thirds or right to the ground.  Fresh foliage will emerge and it will likely rebloom.  Excellent in the front of a perennial bed, entry garden, as an accent plant and for long lasting cut flowers.

 

Centaurea montana ‘Gold Bullion’
Centaurea montana 'Gold Bullion'

  • Common Name:  Perennial Cornflower, Mountain Cornflower, Bachelor’s Button, Montana Knapweed, Mountain Bluet
  • Plant Type:  Herbaceous perennial
  • Height:  12-18:
  • Spread:  12-24”
  • Sun/Shade Requirements:  Full sun to part shade
  • Water Requirements:  Low to average, drought tolerant
  • Soil Requirements:  Average well drained soil.
  • Growth Habit:  Upright with spreading mounds
  • Bloom Time: May to June, light reblooming if deadheaded.
  • Bloom Color: Cornflower blue with red-blue centers and black edged bracts.
  • Bloom Form:  2” showy flowers with spider-like, fringed petals, born singly on strong stems.
  • Foliage:  Foliage is golden yellow.  Large lower leaves are 7” and lance shaped, diminishing in size progressing up the stalk.
  • Fragrance:  None
  • Pest and Disease Resistance:  Deer and rabbit resistant.  May be susceptible to stem rot in moist conditions.
  • Fertilize:  Feeding is not required, may be fertilized in early spring if soil is unusually poor.
  • Maintenance:  Divide every 2-3 years in spring or fall.
  • Other:  Attracts butterflies
  • Hardiness:  Zones 3-8

‘Gold Bullion’s’ golden, chartreuse yellow foliage color is best achieved in full sun.  In too much shade, the golden foliage will become lime green.  By autumn the golden color will begin to fade.  Remove any leaves that have reverted to true green, as well as all green seedlings.  ‘Gold Bullion’s’ golden foliage contrasts the deep cornflower blue blooms beautifully.  Wonderful when planted with purple foliaged plants. 

Rich fertile soil should be avoided to minimize spreading by underground rhizomes.  Colonies can be formed quite rapidly in optimum growing conditions, including cool northern climates.  Spent blooms should be removed to minimize self seeding and to encourage reblooming.  Or cut flowers for fresh or dried arrangements.  The plants do not come up true from seed, producing variants of this hybrid often with green foliage.

By midsummer the foliage may become unattractive.  If so, cut the whole plant to the ground, or back by two-thirds, and fresh foliage will emerge.  Additional blooming may also occur.

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