Centaurea cyanus
Centaurea cyanus, commonly known as cornflower, bachelor's button, bluebottle, boutonniere flower, hurtsickle or cyani flower, is an annual flowering plant in the family Asteraceae, native to Europe. "Cornflower" is also used for chicory, and a few other Centaurea species; to distinguish C. cyanus from these it is sometimes called common cornflower. It may also be referred to as basketflower, though the term also refers to the Plectocephalus group of Centaurea, which is probably a distinct genus.
It is an annual plant growing to 16-35 inches tall, with grey-green branched stems. The leaves are lanceolate, 1–4 cm long. The flowers are most commonly an intense blue colour, produced in flowerheads (capitula) 1.5–3 cm diameter, with a ring of a few large, spreading ray florets surrounding a central cluster of disc florets. The blue pigment is protocyanin, which in roses is red.
In the past it often grew as a weed in crop fields, hence its name (fields growing grains such as wheat, barley, rye, or oats are known as corn fields in the UK). It is now endangered in its native habitat by agricultural intensification, particularly over-use of herbicides, destroying its habitat; in the United Kingdom it has declined from 264 sites to just 3 sites in the last 50 years. In reaction to this, the conservation charity Plantlife named it as one of 101 species it would actively work to bring 'Back from the Brink'.
It is also, however, through introduction as an ornamental plant in gardens and a seed contaminant in crop seeds, now naturalised in many other parts of the world, including North America and parts of Australia.
Cultivation
It is grown as an ornamental plant in gardens, where several cultivars have been selected with varying pastel colours, including pink and purple. Centaurea is also grown for the cutflower industry in Canada for use by florists. The most common colour variety for this use is a doubled blue variety such as 'Blue Boy' or 'Blue Diadem'. White, pink, lavender and black (actually a very dark maroon) are also used but less commonly. It is also occasionally used as a culinary ornament. Cornflowers have been used and prized historically for their blue pigment. Cornflowers are often used as an ingredient in some tea blends and herbal teas, and is famous in the Lady Grey blend of Twinings. Wild cornflower floral water is produced in Provence, France. It is obtained by steam distillation which can be used as a natural mild astringent and antiseptic to prevent eye infections as well as an alcohol-free natural toner. A relative, Centaurea montana, is a perennial plant which is also cultivated as a garden plant. Cornflowers germinate quickly after planting.
Light requirements: full sun. Water requirements: high-average water daily. Soil pH requirements: neutral (6.6-7.5) to mildly alkaline (7.6-7.8).
It flowers from June until August.
The cornflower is considered a beneficial weed, and its edible flower can be used to add colour to salads.
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