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Gardening: Plant Hunters Article - June/July 23

Cornflowers and Knapweeds by Martin Blow

We all love to see cornflowers growing wild, although it is a rare sight these days. These wildflowers are the annual Centaurea cyanus that can be grown from seed each year. There are, however, lots of perennial types that have the same shuttlecock flowers but come up year after year in the garden. Cornflowers and knapweeds all belong under the name of Centaurea which harks back to the ancient Greek legends of their healing properties.

It isn’t just the flowers that provide garden interest. Many varieties have grey leaves often divided into lacy filigree. The flower buds are clothed in woody, shiny or spiny scales and can be almost jewel-like. One of my favourite natives is Centaurea nigra, known as hardheads or black knapweed. It grows in all kinds of grassland and is a favourite of bees and butterflies all through the summer. Another native, greater knapweed (Centaurea scabiosa) grows well in our garden seeding around gently.

There are many varieties suitable for the garden that enjoy the rough and tumble of the crowded border or naturalistic planting. The giant yellow knapweed, Centaurea macrocephala, has perhaps one of the most iconic flowers of the genus. The large globular yellow flowers resemble a giant thistle or cardoon flower. For a more refined look to the border choose the dainty Eastern knapweed (Centaurea orientalis).

For an upright, purple-pink flowered cornflower you can’t do much better than the new variety “Caramia”. This will rebloom if cut back hard after flowering and grows to about 1ft 6in tall.

Most gardeners will know Centaurea montana, the mountain bluet, for its blue flowers, grey-green leaves, and low growing, running habit. There are lots of new colours available now: the white-flowered Alba; Carnea is flesh pink; Purpurea is royal purple, and Purple Heart is white with an attractive purple centre. The new variety Jordy is a “must have” plant with large burgundy flowers. It is more upright and reblooms through to the autumn if cut back hard after each crop of flowers finish.

Centaureas will grow in most soil types including sticky clay but if your soil is very acid, you may find a dressing of powdered limestone each spring is useful. Spreading types can be divided before or between flowering.

Centaurea are one of the best bee plants in the garden, particularly for bumblebees. We have spotted many species of bumblebee regularly visiting them in large numbers. Butterflies are also attracted by the chance to fuel up with nectar.

Whilst deadheading flowers is useful for us gardeners, it’s well worth leaving seed heads on to allow charms of goldfinches (and occasionally Redpolls) to come take their fill of the seeds, even in mid-summer and particularly through the winter.

These easy to grow flowers are sure to please the gardener as well as the bees, butterflies and birds.

Janet & I organise Plant Hunters’ Fairs, specialist plant fairs at wonderful locations. Please see for a full list of our 2023 plant fairs. Please check our website for ticketing information and all the latest updates before travelling. Plant Fair Dates for your diary 2023:

Middleton Hall, Nr Tamworth, B78 2AE on Sunday 25th June, entry to Gardens & Plant Fair only £3.50 (special reduced entry price). 1620s House and Garden, Nr. Coalville, LE67 2FW on Sunday 30th July, entry to Garden & Plant Fair £1.