Knapweeds – Centaurea SPP.: Edible & Medicinal Uses of the Cornflower of Wild Plants

Table of Contents

Most local knapweeds (centaurea spp.) look similar to bull thistle. However, you’re more likely to find your knapweed in patches instead of lone like bull thistles. Spotted knapweed (c. maculosa) is noted in Haliburton Flora on the edge of the highway, which is where I’ve seen it too. Another centaurea is bachelor’s buttons, as pictured immediately below. It’s been used in landscaping and can be aggressive, although some people find them controllable. Both are nonnative and rare here.

Cornflower AKA Bachelor’s Buttons / Knapweeds – Centaurea SPP.
Knapweeds -  Centaurea SPP.
Knapweeds – Centaurea SPP.

Edible Uses of Knapweeds

The flowers are edible raw or cooked and make a pretty garnish. The blue flowers of c. cyanus can give tea a nice colour. This pigment can also be used as a natural food dye.

Medicinal Uses of Knapweeds

Knapweed is primarily said to support these body systems:

  • Digestive
  • Integumentary

Medicinal tags include Astringent, Diaphoretic, Diuretic and Vulnerary. See Medicinal tag key for more information.

Common usage includes astringent uses like eye washes and compresses with the cornflower blue c. cyanus.

Multiple species of knapweeds have had their roots and seeds used for sore throat gargles, and in ointments for wounds and skin infections. Especially greater knapweed (c. scaboisa).

Alternative Uses of Cornflowers

A blue ink or dye is obtained from cornflower (c. cyanus) petals when mixed with alum-water. The colour cornflower blue gets its name from this plant! This pigment is used commercially too.

The fresh or dried flowers can be used in arrangements and the dried can be used in potpourri.

Extracts can be used in hair products.

Knapweeds – Centaurea SPP.

Growing Centaurea SPP.

Native thistle, ironweeds, lance leaf coreopsis and bee balm are some alternatives to nonnative knapweeds. Like their lookalike nonnative thistle “Canada” thistle, spotted knapweed can spread uncontrollably in disturbed ground like agricultural fields. Like many nonnative plants they are allelopathic too, which means they make toxins in their roots to stunt plants around them. People have given mixed reports regarding the blue-flowered bachelor’s buttons aggressiveness. If you need to remove either, try and get all the deep taproots and keep rechecking the spot for a couple years.

There are a handful of moths and butterflies whose larvae eat knapweeds, and they’ve been used to biologically control the plant. And American goldfinches may eat the hard kernel-like seeds. But at the same time the species is still crowding out higher quality native food sources for animals.


And the Usual Cautions:

1) Most medicinal herbs, if edible, are meant to be eaten in moderation, even sparingly. Some require extra preparation. Tannins are toxic if consumed in excess.

2) People can be allergic or sensitive to nearly any plant; try new herbs one at a time at your own risk. For instance, saponins commonly cause stomach upset.

3) For medicinal use, I must recommend receiving a diagnosis and working with a reputed health care provider. I generally do not post specific treatments and dosages because I think that is best between you and your health care provider, and ideally monitored.

4) Anyone pregnant, nursing, or taking prescription drugs should talk to a health care professional before adding new food items to their diet.

5) Many plants have look-a-likes, and sometimes they are poisonous.

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A Modern Herbal (Volume 2, I-Z and Indexes)

The Herb Book: The Most Complete Catalog of Herbs Ever Published (Dover Cookbooks)

Reader’s Digest Magic and Medicine of Plants

Illustrated Encyclopedia of Herbs

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