How to Grow Centaurea Plants in your Garden

Gardener's HQ Guide to Growing Cornflower, knapweed, and Basket Flower

There are many commonly grown garden plants that belong to the Centaurea genus, these include but are not limited to cornflower, Bachelor's buttons, Basket flower, Knapweed, Ragged robin, and Sweet sultan.

The variety means that the genus contains plants that are hardy annuals, biennials and perennials.

This means that the flowering season is also very variable, though annuals tend to flower from late in spring to late in the summer, whereas perennial members of Centaurea tend to flower in the spring or summer.

They tend to have deeply coloured petals of varying colours and vary in height from 30 to 90 cm, they make ideal plants for growing in simulated wild gardens.

Centaurea montana
Centaurea montana by Alexandre Dulaunoy.

Centaurea macrocephala
Centaurea macrocephala by Matt Lavin.

Centaurea Growing and Care Guide

Common Names: Knapweed, Starthistle, Loggerheads, Bluets, Sweet Sultan, Basket Flower, Cornflower, Ragged robin, Bachelor's buttons.
Life Cycle: Hardy annual. Hardy biennial. Hardy perennial.
Height: 12 to 36 inches (30 to 90 cm).
Native: Europe.
Family: Compositae, Asters

Growing Region: Annuals: zones 1 to 10; perennials: Zones 3 to 10.
Flowers: Spring and/or summer.
Flower Details: Blue, red, pink, yellow, white. Pompom-like. Fine petals.
Foliage: Weedy. Elongated lobes, often spiny.

Sow Outdoors: Cover seeds. Use successive sowing for continued blooms. Before last frost or autumn. Spacing 6 to 12 inches (15 to 30 cm).
Sow Indoors: Germination time: one to five weeks. Darkness. Temperature 60 to 70°F (15 to 21°C). Seven or eight weeks in advance. Transplant annuals outdoors at the end of spring. Perennials and biennials can be planted out in either late spring or early autumn.

Requirements: Full sunlight. Good drainage. Soil pH 5.5 to 7. Ordinary soil. Feed in spring. Regular watering. Deadhead. Stake taller species. Cut back perennials following blooming. Divide perennials in spring in cool areas or autumn in warmer areas.
Miscellaneous: These plants are attractive to insects, therefore they can be grown as an alternative source of food for insects when growing crops.

How to Grow Centaurea

If planning to grow cornflower-like species outdoors then the seeds should be sown in sunny areas of the garden that have soil with good drainage, ideally the pH should be from 5.5 to 7.

It is best to sow the Centaurea seeds successively from just before the last frost of spring, or in the autumn.

If first growing indoors, then they normally take about one week to one month to germinate. Start off about 6 or 7 weeks before you plan to put them out into the garden, in the late spring.

Caring for Centaurea Species in the Garden

Centaurea require regular watering and ideally should be fertilized in the spring.

If you require more seeds then Centaurea annuals will self seed and you can divide perennial varieties in the spring.

Common Questions

How many members does the Centaurea genus have?

The Centaurea genus consists of about 350 to 600 species.

Do members of Centaurea make a good garden or landscaping plant?

Yes, many species of Centaurea such as Centaurea cyanus (Cornflower) are popular garden plants due to their vibrant blooms.

Which Centaurea species are most frequently grown by gardeners?

Centaurea cyanus (Cornflower) and Centaurea montana (Mountain Bluet) are often chosen by gardeners for their vivid, blue flowers.

Are members of the Centaurea plant genus fragrant?

While some Centaurea species may have a mild scent, they are not typically known for their fragrance.

What is the perfect location to grow Centaurea?

Centaurea plants enjoy full sun and well-drained soil. They are fairly drought-tolerant, making them ideal for xeriscaping.

Is Centaurea invasive in the USA?

Some species like Centaurea diffusa (Diffuse Knapweed) are considered invasive in certain regions of the USA due to their aggressive growth.

How do I remove Centaurea plants from my garden?

To remove Centaurea, manually pull out the plants, ensuring to remove all roots. Repeated mowing can also help control their spread.

Summary

The Centaurea genus is part of the Asteraceae family and is native to the Old World. This diverse genus includes well-known species like the Cornflower and Bachelor's Button, beloved for their thistle-like flowers that bloom in a variety of colors.

To cultivate Centaurea, plant them in full sun, in well-drained soil. They can be grown from seeds sown in spring or fall, or by division in the fall. Regular watering is needed, but they are fairly drought-tolerant once established. Deadheading can promote prolonged blooming.

I hope that you enjoyed this guide on how to grow Centaurea plants. You may also enjoy the following Gardener's HQ growing guides: How to grow Zinnia angustifolia and Argyranthemum frutescens plants.