Centaurea macrocephala Seeds | Globe Cornflower
LATIN NAME: Centaurea macrocephala
COMMON NAME: Globe Cornflower
Plant Profile
Centaurea macrocephala comes from the Caucasus and northeastern Turkey, where it grows in mountain meadows and on rocky slopes. It is a clump-forming perennial 1 to 1.5 m tall, with coarse, lobed leaves and a stout stem that carries a single flower head 5 to 7 cm across.
The head is a thistle-like button of golden yellow florets, surrounded by overlapping brown, papery bracts that give it a globe shape and a texture like dried scales. The bracts are the reason the plant is grown as much for drying as for the border, since they keep their shape and colour for years after cutting.
The plant is one of the largest of the knapweeds, and it ranks among the few that is grown for ornament rather than being a weed. It flowers in early and midsummer, and the heads are produced over several weeks, which makes it a useful cut flower as well as a border plant.
The genus name comes from the Centaur Chiron, who was said to have used a knapweed to heal a wound, and the family name comes from the same story. The common name globe cornflower refers to the shape of the head, and it is a better description than the botanical name.
Science & Biotechnology
Centaurea is a genus of about 700 species in the Asteraceae, and it includes cornflower, knapweed and a number of serious agricultural weeds. The genus is characterised by the involucre of overlapping bracts, which in this species are papery and brown rather than green. The yellow colour is produced by carotenoids in the florets, and the brown of the bracts is produced by oxidation of phenolic compounds as the head matures. That oxidation is why the bracts keep their colour when dried: the pigments are already stable, and there is nothing left to fade.
The genus is divided into sections on the basis of flower colour, bract shape and chromosome number, and the classification has been revised several times. C. macrocephala belongs to a group of yellow-flowered species from the Caucasus and Turkey, which are more closely related to each other than to the blue cornflower of Europe.
The plant is pollinated by bees and by butterflies, and it is self-incompatible, which means that two different plants are needed for a good seed set. That is why a single plant in a garden often sets little seed, and why a group of three or more is better for both seed and display.
Uses & Benefits
It is used at the back of a border, in a wild garden and in a cutting garden, where its height and its unusual heads make it a focal point. It is also one of the best plants for drying, since the bracts hold their colour and shape and the heads can be used in winter arrangements.
The flowers are visited by bees and by butterflies, and the plant is a good source of nectar in early summer. It is not edible, and the foliage is bitter and unpalatable, which is one reason it survives in rough grassland.
In a border it needs staking in a windy site, since the heads are heavy and the stems are hollow. It combines well with grasses, with verbascum and with other tall summer perennials, and it ranks among the few yellow flowers that works at the back of a border without looking coarse.
For drying, cut the heads when the bracts are fully formed but before the florets fade, and hang them upside down in a dark, airy room. They will keep for years, and they are useful in arrangements where a strong shape is needed without much colour. The rest of the Asteraceae here runs to Centaurea stoebe, Centaurea americana and Euryops pectinatus.
Growing from Seed
Under cover in late winter, six to eight weeks before the last frost, at 18 to 21 °C, with just enough compost to hide the seed. The seedlings arrive somewhere between two and three weeks. The seed is large, germination is dependable, and the seedlings grow away quickly. Pot on into 9 cm pots at 15 °C. Plant out in spring or early autumn, 45 cm apart, in full sun and well-drained soil. The plant tolerates poor ground and needs no feeding; rich soil produces tall growth that needs staking.
Water in the first season, then only in severe drought. Stake the stems in a windy site, or plant it at the back of a border where the heads can lean without blocking the view. Cut the flowered stems back after flowering if you do not want seed, or leave a few for the birds.
Divide clumps every three or four years in spring, discarding the woody centre. The plant self-sows where it is happy, and seedlings can be moved while they are small. It is hardy to about -25 °C and needs no winter protection.
Our Take
Globe cornflower is a plant for the back of a border and for the drying basket. It is tall, bold and unusual, and it lasts for years in a dried arrangement, which is more than most perennials can offer. Grow it where its height can be seen, stake it against wind, and cut it for drying. It is not a plant for a small garden, but it is a good one for a large border.
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