Cornflower – Centaurea cyanus

The Cornflower is so named because it was once a wild flower growing as a weed in fields of corn. It makes a pleasing plant for a tub or window-box now it has been tamed. Those varieties of the Cornflower that are best in pots grow to about 30cm (12in) and there is a range of flower colours to choose from.

The Cornflower is relatively easy to grow and is not affected by many pests. However, it does suffer from some diseases so it needs to be given a thorough visual examination periodically.

The Cornflower can be between 30-90cm (1-3ft) high. The plant is bushy and has lance-shaped grey-green leaves that are slightly serrated. The flowers are about 4cm (1½in) across and borne on sprays that branch. The flowers are produced all through the summer.

There are two groups of varieties of Cornflower. The taller ones such as ‘Blue Diadem’ are best grown in beds in gardens but the smaller varieties are best in pots and tubs. The varieties to pick are ‘Dwarf Blue’ for a striking blue, ‘Polka Dot’ for a mixture and ‘Dwarf Rose Gem’ for a cheerful red.Cornflower - Centaurea cyanus

Cornflower is an annual that produces beautiful flower heads of blue, red, purple, pink and white.

Propagation

You can sow the seeds of the Cornflower in either March—April or September. Always sow seeds from packets labelled for the current year. If you sow in the spring, make a series of sowings, with about a 14 day gap between, to extend the flowering season. Sow the seeds in an open soil-based compost.

Plants can be given an early start if seeds are sown under cover in seed trays or pans. They have to be hardened off and then planted outside when there is no longer any danger of frost.

When the seedlings have grown up to a respectable height you can thin them out to prevent overcrowding. Plants sown in September are larger than those sown in spring so give them more space than the spring-sown seedlings.

Pests And Diseases

A white powdery coating forming on the plant’s surface could be caused by mildew.

Treatment: Remove the affected parts and spray with a fungicide.

Brown spore-like accumulations on the undersides of the leaves of the Cornflower are caused by rust.

Treatment: Remove the affected areas and spray the plant with an appropriate chemical agent. If one application does not work, you may have to carry out the process again.

PLANT CARE

Needing the minimum of care, the Cornflower can almost fend for itself in a large tub or window-box, providing it gets plenty of sunshine and is watered when the top layer of compost has dried out.

  • Potting: Put in a tub containing rich, soil-based compost.
  • Water moderately but be sure to let the upper part of the compost become dry between waterings. In the summer beware of long, hot periods that might dry out the compost completely.
  • Feeding: Feed occasionally with a proprietary liquid fertilizer, especially during the growing season.

BEST GROWTH ENVIRONMENT

  • Light: This plant does well in positions of good light and enjoys full sun.
  • Temperature: The plant will grow outside quite happily and is completely hardy, even in cold Scandinavian climates.

Buying Tips

  • The plant is grown annually from seed sown either in early spring or late summer. It is offered in trays of bedding plants, modestly priced in late spring.
  • Buy healthy looking plants with plenty of flower buds and with a neat bushy shape or buy seeds sealed in airtight packs. It is usually grown from seed as an annual.

The Cornflower, with its charmingly coloured flowers, is a hardy annual that will thrive outdoors in a sunny tub or window-box. It will also do well in a conservatory.

Centaurea is the cornflower, and although the annual forms are best known, there are several perennial species worth growing. They are easily cultivated in ordinary garden soil and are usually grown because of their attractive, often silvery-grey foliage. They may be propagated by division in the spring.

C. montana makes good bushy plants varying in height from I to 2 ft and having rather thin-looking, violet-blue flowers in July. It has varieties with lighter blue, pale pink and white blooms.

C. dealbata has thistle-shaped, rosy-purple flowers on 18-in. Stems which appear from July until October, and it has a cyclamen-red variety. C. ruthenica has lemon-yellow blooms which last well.

 

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