Centaurea trial 2024–2026

Objectives and purpose of the trial

The focus of this trial is to showcase a range of hardy herbaceous Centaurea (cornflower or knapweed) cultivars available to gardeners. The trial at RHS Wisley, Surrey, will assess the performance of new cultivars that are not only visually appealing and popular but also feature long flowering periods and come in a variety of colours. Those that perform best will be awarded the RHS Award of Garden Merit (AGM).
Showy yellow flower-heads of Centaurea macrocephala in summer
Thistle-like flowers of Centaurea montana ‘Joyce’ make a statement

Judges and criteria

Judging criteria

The following factors are all taken into consideration as part of the judging of the trial:

  • Floral impact and duration of flowering
  • Use as a foliage plant

  • How much and how quickly each plant spreads

Suppliers to the trial

List of plants in the trial

View all of the Centaurea on trial at RHS Wisley
  • Centaurea affinis
  • Centaurea scabiosa subsp. alpestris 
  • Centaurea calocephala
  • Centaurea bella
  • Centaurea carniolica
  • Centaurea cheiranthifolia
  • Centaurea dealbata
  • Centaurea dealbata ‘Steenbergii’
  • Centaurea glastifolia
  • Centaurea ‘Caramia’
  • Centaurea jacea
  • Centaurea ‘John Coutts’
  • Centaurea ‘Jordy’
  • Centaurea macrocephala
  • Centaurea ‘Larch Cottage Electric Blue’
  • Centaurea montana
  • Centaurea montana ‘Alba’
  • Centaurea montana ‘Amethyst Dream’
  • Centaurea montana ‘Amethyst in Snow’
  • Centaurea montana ‘Blewit’
  • Centaurea montana ’Carnea’
  • Centaurea montana ’Joyce’
  • Centaurea montana lilac-flowered
  • Centaurea orientalis
  • Centaurea montana ’Parham’
  • Centaurea montana purple-flowered
  • Centaurea montana ‘Purple Heart’
  • Centaurea nigra
  • Centaurea simplicicaulis
  • Centaurea triumfettii subsp. stricta
  • Centaurea from Turkey
RHS Award of Garden Merit logo
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Handy tools and information

Get in touch

For more information on our RHS Plant Trials or to access older trial reports, please get in touch with our team via email at [email protected].

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