Knapweed – Centaurea species

Charming old-fashioned flowers. The thistle-like flowers of the perennial knapweeds bring a subtle splash of colour to the summer border. There are many types of this easy-going plant to choose from, blooming at different times throughout the summer.




Fertilize soil if especially poor. Plant new specimens. Divide and replant old ones. Mulch (cover surrounding ground) with compost or similar bulky substance.


C starts to bloom.



The main flowering period. Stake larger specimens if necessary. Deadhead (remove dead flower-heads) as the first flush fades. Watch out for powdery mildew and spray if required.



The last flush of

C. ’John

Coutts’ finishes.

Plant bought knapweeds.


Remove any stakes.

Cut dead foliage down, unless weather is very cold.



Allow knapweed to lie dormant.


Dig knapweed up and divide every three years. Replant the most vigorous divisions in the original spot and discard the weaker centre of the clump. Do this in autumn or spring and, at the same time, add fertilizer or compost. 1, PRUNING, 1

If the weather is particu-, larly cold in autumn, or you, have planted the knap-, weeds in an exposed site do not cut the plants down, to the ground

Instead, wait until just, before new shoots start to appear in the springtime.

Leaving the withered stems on the plants will provide the tender crowns (the points where the roots and stems join) with some protection from the frost and rain



To dry knapweed for indoor arrangements, hang small bunches upside-down in a dry room. The flowers will shrink slightly as they dry. To preserve the colour of the blooms, pre- dry them before hanging indoors by putting in a cool oven for 30 minutes.


Name C. dealbata, Colour pink, Height (cm) 100, Flowering

June July

C. dealbata ‘Steenbertfii’, crimson; white centre, 60, July-August

C. hypoleuca ‘John Coutts’

C. macrocephala, rose-pink; cream centre yellow, 60 100, June, Sept-Oct


C. montana, blue; red centre, 45, May-June

C. montana ‘Alba’, white, 45, May-June

C. montana ‘Carnea’, pink, 45, May-June

C. montana ‘Parham Variety’, purple, 45, May-June

Knapweeds are typical country-garden plants which grow strongly and bloom reliably. The flowers are good both for cutting fresh and for drying.

Knapweeds are versatile and adaptable plants. They provide a dashing border display yet are easy to care for, which makes them ideal for busy gardeners.

There are several species of knapweed, but all have similar flowers: a rounded base with slender, coloured petals in florets (small flowers together on a flower-head). There are several different flower colours and all attract many insects.

Which knapweed?

Elegant C. montana goes well with lupins in an early summer border. Its dense mat of green leaves supports floppy stems topped with large, feathery cornflower blooms.

C. dealbata is a larger plant, with lilac-pink flowers among grey-green leaves. It is easy to grow and free flowering, but needs staking.

C, hypoleuca has large, cream-centred rosy flowers and pale leaves which are delightful on their own. It blooms a second time in autumn. Removing the flower-heads as they fade ensures it is seldom out of flower all summer. The pretty seed heads look like silver daisies.

C. macwcephala has large golden flowers on tall, thick stems, which make hand some dried flowers.

Growing from seed

You can raise knapweed from seed.

Sow seeds in April in a cold frame.

Move them to a nursery row for the summer.

Plant out in the flowering position in autumn or the following spring.

Planting and care

Plant nursery-bought specimens out in October or March in a reasonably fertile, well-drained site. Find a sunny or partially shaded spot. Avoid windy sites for larger species or you will have to stake them.

Knapweed grows particularly well on chalky soil. It spreads quickly if given a good position.



Plant in full sun or partial shade. Make sure the site is not exposed to strong winds, especially if planting larger species.


Prefers well-drained, lime-rich soil, but also thrives on any reasonably fertile soil. Avoid waterlogging.


Deadhead (remove dead flowers) throughout the summer to encourage new blooms. Stake taller plants if they flop badly. Divide every 3 or 4 years to keep plants flourishing.


Pests are seldom a problem, but powdery mildew can be a nuisance. This appears as a white coating on plants, particularly in hot, dry weather and on closely spaced plants. Leaves can yellow and fall off and the whole plant may droop.

Mulch (cover ground) with leaf-mould in spring and water during dry spells in summer to try to prevent an outbreak. If powdery mildew does attack, spray with a suitable fungicide. Remove and destroy any diseased debris in autumn.

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