How to plant Centaurea

Centaurea is a diverse genus ranging from annual Cornflowers to hardy perennial Knapweeds. In this guide we will refer to the hardy perennial varieties. Originating from damp meadows, plant breeders have transformed these informal plants into well behaved garden beauties with border-worthy growth habits. Despite their name, Knapweeds won’t spread and take over your garden but instead form neat, compact clumps. Growing reliably on most sites and soils, Knapweeds are indispensable for bringing a traditional feel to the front of cottage garden borders and informal wildlife gardens. The shaggy, nectar rich blooms are loved by bees and butterflies in early summer, with a second flush often appearing in late summer.

How to plant

  • Plant Centaurea in spring between February and May, ideally within a week of delivery.
  • Soak the roots in water for 3-6 hours prior to planting. Pot into temporary 2 litre (or 15-20cm diameter) pots, using a good quality multi-purpose compost.
  • Plant so that the roots are fully submerged and the crown is just level with the soil surface. Any shoots or leaves which have emerged should be exposed above the soil surface.
  • Grow them on in a sheltered spot outside. They can be transplanted to suitable final positions after 2-4 months, or once growth is established and the plant is easily removed from the pot with the soil intact.
  • Centaurea prefers a moist, fertile and well drained soil, but isn’t fussy about soil type. It will happily thrive in clay, sandy or stony soil.
  • Choose a position in full sun or light shade where it will receive some sun throughout the day as this promotes flowering.
  • This perennial is fully hardy and does not require winter protection.
  • Water-in after planting and keep hydrated over summer, particularly during the first year.

Aftercare

  • Centaurea will start to produce new growth in spring with flowers appearing around from May to July. Each year, as the clump grows, the plant will produce more flowers.
  • Centaurea may benefit from some twiggy sticks or other form of support for its stems as the summer progresses. These are best put in place as new growth emerges in spring.
  • Deadhead the faded flowers of Centaurea to encourage more blooms to develop. If chopped back immediately after the first flowers fade, you may see another flush of blooms later in summer. This also prevents the stems collapsing, as the plants will produce new stems from the base.
  • The stems will naturally die back in late summer and autumn. They can then be cut back to around 3cm above ground level.
  • Overcrowded clumps should be lifted and divided in early spring or late autumn.