A robust and versatile group of traditional garden and wildflower plants, which provide reliable results on most soil types. The charming button shape flowers are not just available in traditional blues but also in a wide range of pastel colours.
Asteraceae (Daisy family)
Botanical Name: Centaurea
Common Names: bachelor's buttons, bluebottle, cornflower, hardheads, knapweed, loggerheads, sweet sultan.
Foliage: Grey-green or silvery white, pinnately or deeply lobed leaves, often with a hairy underside.
Flowers: button, thistle or quilled globe like blooms. Colours range from white and blue to mauve, purple, pink, yellow and orange (depending on variety).
Flowering Period: spring to summer.
Soil: any fertile garden soil that is moist but well-drained.
Conditions: Best in full sun. North, east, west or south facing aspect, in an exposed or sheltered possition.
Habit: Spreading / Branched.
Type: hardy annuals and perennials.
Origin: Northern temperate zone and South America.
Hardiness: Most species are fully hardy throughout the UK (annuals usually die after flowering at the end of the season). A few varieties are tender to half-hardy.
These carefree plants will thrive in any sunny border, container or even a window-box. In fact these robust plants will grow almost anywhere if given full sun, even in poor soil. They will also tollerate shade for part of the day.
Very easy plants to grow from seed, requiring little care and attention. Can be grown in virtually any soil type from heavy clay to shallow chalk and lighter sandy soils, as long as it is well drained and watered well. All forms do very well in chalky soil.
Common varieties are ideal for cottage, prairie or informal gardens, also wildlife gardens and wildflower meadows.
Tall varieties can reach over 3ft and are good for cutting.
Note: Bide-a-Wee Cottage Gardens, in Northumberland, hold the National Plant Collection of Centaurea.
Most varieties of Centaurea are very robust and will usually tollerate neglect and dry conditions. Annuals are prone to prolific self-seeding and may become quite invasive under certain conditions.
Deadhead regularly to extend the flowering period.
Prone to powdery mildews. Generally disease free
Sow seeds of annuals from March to May or in September for flowering the following year. Divide perennials in autumn or spring. Take cuttings of tender perennials in late summer and over winter young plants under glass. Plant out in late spring once frosts have passed.
There are sizes and types of cornflower to suit most gardens from low growing mat forming to the giant C. macrocephala, which reaches up to 4ft (1.2m).
C. cyanus (hardy annual), in blue & paler shades of lilac, pink & white. Height up to 3ft (1m). The following good forms have been developed from this genus: 'Jubilee Gem' with large double dark blue flowers, 'John Coutts' large pink flowers, 'Polka Dot Mixed' mixed colours good for bedding, 'Rubra' rose-red flowers and 'Rosea' pink flowers, to name but a few.
C. dealbata steenbergii (perennial), with deep pink flowers, May to June. Height 2ft (60cm), spread 18in (45cm).
C. hypoleuca 'John Coutts' (perennial), with pink flowers, May to July. Grey leaves. Height 1ft (30cm).
C. montana (perennial), good forms include 'Rosea' pink flowers and 'Alba' white flowers.
C. moschata (sweet sultan), a hardy annual or biennial with red-purple, pink, yellow or white scented fluffy flowers. Height 2ft (60cm), spread 9-12in (25-30cm).
C. macrocephala, a tall perennial variety with yellow globed flowers, June-August. Height 4ft (1.2m)
C. orientalis, a perennial with yellow, tufty flowers. Height 18in (45cm)
C. rutifolia (Dusty Miller), a half-hardy evergreen perennial with pink flowers. Height 1ft (30cm)