With its deep purple, almost black flowers, Buddleja ‘Black Knight’ AGM is probably the darkest-flowered buddleia of all. Just look at the long heads - or botanically speaking, elongated panicles - of flowers on arching branches. The honey-fragrant flowers are a magnet to butterflies and bees, so it’s an ideal addition to a wildlife garden.
Buddleias are easy-going shrubs and will grow in any well-drained soil and in all but north facing situations.They are excellent for a low-maintenance border, cottage or informal gardens.
If you have the time, deadheading will encourage them to produce more flowers and minimise unwanted seedlings. You’ll need plenty of room as they are large, vigorous plants that can grow up to 3m (10ft). Flowers are produced on the current year’s growth so it’s a late winter or early spring job to prune back to three or four buds.
Plant B.‘Black Knight’ AGM with blue agapanthus or purple phlox to harmonise with the flower colour, or with yellow coneflowers or Leucanthemum to pick up the orange centres. Spherical or daisy-like flowers such as globe thistle will be a contrast in shape, as will plants with spiky and strappy foliage.
As you would expect, we have this lovely shrub growing in the Cottage Garden at RHS Garden Rosemoor, along with other cottage garden favourites: shrubs such as Cistus, roses and Deutzia and herbaceous perennials like Veronica, Geranium and Phlox. We’ve added a touch of formality by placing a standard rose in the mix; the icing sugar pink Rosa Bonica AGM. This combines deliciously with the deep-purple buddleia flowers. The aster Symphyotrichum novae-angliae 'Harrington's Pink' AGM forms a mass of pretty pink flowers at a lower level.
In the Long Border, we have grouped it with other tall and imposing plants, including purple-blue Nepeta parnassica, pink-lavender Veronicastrum sibiricum.
B. 'Black Knight' AGM is normally stocked in the Rosemoor Plant Centre along with many of the other plants mentioned; you only need a few to make a bold statement in your garden.