Buddleia ‘Black Knight’

Buddleia 'Black Knight' (Buddleja davidii 'Black Knight') carries the darkest flower in the butterfly bush group: long tapered spikes of near black violet, honey scented, and busy with butterflies from late spring until the cold arrives. It reaches about 2.5m tall and 2m wide, deciduous, and because it blooms on new wood a hard prune each winter keeps it dense and covered.

Why you'll love it

• The deepest purple of any buddleia. Spikes 20 to 30cm long in a violet dark enough to read as black against pale foliage.
• Butterflies and birds work it all summer. The flowers are nectar rich, and small birds follow the insects in.
• Fast from a small plant. It puts on real size in a single warm season, so tube stock is not a long wait.
• Tough where other flowering shrubs sulk. Frost hardy, drought tolerant, wind tolerant and content in poor soil.
• Honey scent on warm evenings. Strongest at dusk, which makes it worth planting near a seat or a path.

Where it works best

Mass planting and borders. Plant 1.5m apart for a massed border. Three or five in a drift gives a far better show than a single plant, and the spacing leaves room to prune each one properly.

Informal screening. At 1.5m apart it makes a soft summer screen along a fence. Be clear eyed about it: this is deciduous, so the screen disappears over winter.

Feature planting. One plant at the back of a sunny bed carries the mid to late season, when the spring shrubs have finished.

Growing Buddleia 'Black Knight' in Australia

Position and climate. Full sun, and plenty of it. This is a cool temperate, warm temperate and Mediterranean plant, at home in the southern highlands, the tablelands and the drier southern capitals. It is not the pick for tropical or humid subtropical gardens, where the spikes rot before they open.

Soil. Drainage matters more than fertility. It grows in poor, stony and sandy ground without complaint, but it will not sit in wet clay, so mound the bed if drainage is slow.

Water and feed. Water weekly through the first summer, then only in long dry spells. A light dressing of complete fertiliser in early spring is enough. Overfeeding gives you leaves instead of flowers.

Pruning. Cut the whole plant back to about 40cm in late winter, every year. Deadhead spent spikes through the season: it keeps new flowers coming and cuts down the seed it sheds.

What to expect when it arrives

It is sold as tube stock, so the plant that arrives is young, single stemmed and often under 30cm. That is the right way to buy a buddleia. They travel well at this size, establish quickly, and a tube planted in spring will usually flower by its first or second summer rather than waiting years.

One honest caution: this species sets abundant seed and is listed as an environmental weed in parts of cooler Australia. Check your local council or state listing before planting, keep it away from bushland and waterways, and deadhead. Delivered Australia wide, delivery from $29.95. Every plant carries our 30 day healthy plant guarantee.

Plant care guides and related reading

• More plants that feed bees and butterflies
• Browse the deciduous shrub range
• A beginner's guide to pruning shrubs
• Other fragrant plants for the garden

Common questions

When and how hard should I prune it?

Late winter, hard, down to roughly 40cm. It flowers only on the current season's growth, so a plant left unpruned gets tall, bare at the base and shy of bloom.

Will it self seed in my garden?

It can. Deadheading through the season removes most of the risk, and in bushland areas or near creeks it is worth choosing a sterile hybrid instead.

Does it lose its leaves?

Yes, it is deciduous, and in cold gardens it stands bare from late autumn until spring. In mild coastal gardens it may hold a few leaves, but do not rely on it for year round cover.