Butterfly Bush – Buddleja Davidii ‘Black Knight’

Butterfly Bush – Buddleja Davidii ‘Black Knight’

Buddleja davidii (spelling variant Buddleia davidii), also called summer lilac, butterfly-bush, or orange eye, is a species of flowering plant in the family Scrophulariaceae, native to Sichuan and Hubei provinces in central China, and also Japan. It was found near Ichang by Dr Augustine Henry about 1887 and sent to St Petersburg. Another botanist-missionary in China, Jean-André Soulié, sent seed to the French nursery Vilmorin, and B. davidii entered commerce in the 1890s.

Flowers are perfect (having both male and female parts), hence are hermaphrodite rather than monoecious (separate male and female flowers on the same plant) as is often incorrectly stated. Ploidy 2n = 76 (tetraploid)

Buddleja davidii ‘Black Knight’ has been one of the most successful davidii cultivars ever released. A selection made by Ruys at the Moerheim Nursery, Dedemsvaart, Netherlands, circa 1959, it was accorded the RHS Award of Garden Merit (record 676) in 1993.

The cultivar is distinguished by its deep purple flowers, reckoned to be the darkest of all the davidii cultivars, but the panicles, at 15–20 cm in length, are smaller than the type. Moreover, the medium-green leaves do not complement the flowers.

‘Black Knight’ is a vigorous large deciduous shrub to 3m – 4m, with somewhat arching growth and lance-shaped leaves, whitish beneath. Flowers scented, deep purple, in elongated panicles at tips of current year’s growth.  The blooms come from early summer to first frost. The foliage is willow-like and grayish green.

The removal of spent flower panicles may be undertaken to reduce the nuisance of self-seeding and encourage further flower production; this extends the flowering season which is otherwise limited to about 6 weeks, although the flowers of the second and third flushes are invariably smaller.

Height: 6 ft. to 10 ft.
Spread: 10 ft. to 15 ft.
Growth Habit:Clumps
Growth Pace: Fast Grower,
Invasive/Aggressive Grower
Light: Full Sun , partial shade
Moisture: Medium Moisture
Maintenance: Moderate
Characteristics: Attracts Butterflies,, Attracts Hummingbirds,, Fragrant Flowers,, Showy Flowers
Bloom Time:  Fall, Summer
Uses:  Beds and Borders,, Cut Flower
Tolerance: Frost Tolerant
Aspect: South-facing or East-facing or West-facing
Exposure: Exposed or Sheltered

Date Planted

Planted as a 2 year (?) plant in fall 2016 in Brugge, BE

Purchase Info

Fall 2016 around Brugge Belgium.


June 23, 2018 in Bloom


Diseases and Problems

Pests : Capsid bug, caterpillars, weevils, mullein moth, leaf and bud eelworms, aphids and glasshouse red spider mite. Fungal leaf spots and diebacks can occur.

Diseases: May suffer from a virus


  • MoistureWell-drained, Moist but well-drained
  • SoilLoam, Chalk, Sand, Clay
  • pHAcid, Alkaline, Neutral

Care: Easy to grow in fertile, well-drained soil in full sun. Prune back or cut to the ground in late winter or early spring. Deadhead regularly.

Propagation: Root semi-ripe cuttings in summer or hardwood cuttings in fall. Sow seed at 66-75°F  in spring.

How to prune summer-flowering shrubs
In early to mid-spring cut back the previous year’s flowering stems to within one or two buds of the older woody framework. Also remove any thin, weak or dead growth.

Fuchsia may need cutting back to near ground level. This stimulates development of strong new growth on which flowers will be produced in late summer.

Pruning as early in spring as possible will give the maximum growing period for the young shoots. Evergreens require a slightly different approach.

After pruning, mulch and feed. Overgrown shrubs may need renovation.

Renovation: Overgrown, old deciduous shrubs can be easily renovated by drastic pruning. After this, annual pruning will stop them getting out of hand again.

When to prune shrubs

Renovate deciduous shrubs between autumn and spring, usually between November and March.

How to prune shrubs

The aim of most pruning is to keep plants healthy and improve flowering, by removing older, less productive wood. Over time, if shrubs have not been regularly pruned, they can become overcrowded, and less productive.

Hard pruning usually stimulates strong new growth, but unfortunately will result in the loss of flowers for a year or two for some shrubs (particularly those, such as Philadelphus and Camellia, that flower on the previous season’s growth).

You can renovate shrubs in two ways: robust shrubs can be completely renovated in one year, but where the response is unknown, carry out a staged renovation instead.