Getting it to bloom

Why won't my Black Knight Butterfly Bush bloom? (and how to make it flower)

Also called Black Knight Buddleia, Summer Lilac, Orange-Eye Butterfly Bush (Buddleja davidii 'Black Knight').

More about black knight butterfly bush

About Black Knight Butterfly Bush

Buddleja davidii 'Black Knight' · also called Black Knight Buddleia, Summer Lilac · flowering

Black Knight Butterfly Bush is a vigorous deciduous shrub producing exceptionally long, deep violet-purple to almost black fragrant flower spikes in summer that are magnets for butterflies, bees, and other pollinators. Fast-growing and easy to manage with hard annual pruning. The ASPCA lists Buddleja davidii as toxic to dogs, cats, and horses.

Plant type: flowering

Watch for — Invasive self-seeding: Prolific seed producer; deadhead promptly after flowering to prevent unwanted seedlings in borders and on walls.

The reasons black knight butterfly bush isn't blooming

Almost every non-blooming black knight butterfly bush traces back to one of these, roughly in order of how common they are:

Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.
Too much nitrogen feed, driving lush foliage at the expense of flowers (very common with general or lawn feeds).
The plant has not been deadheaded, so it stops flowering once it sets seed.
Irregular watering — drought or waterlogging at the budding stage makes buds abort.
It is still too young or was checked by a transplant and is rebuilding before flowering.

Feeding black knight butterfly bush a high-nitrogen general feed and growing it in too little sun — you get a big leafy plant and almost no flowers.

The fix — how to get black knight butterfly bush to flower

Maximise sun. Give black knight butterfly bush the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers.
Switch the feed. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.
Deadhead regularly. Remove spent flowers often to keep it producing more rather than stopping to set seed.
Water consistently. Keep moisture even through budding and flowering — drought-then-flood swings make buds drop.

Light and feeding do most of the heavy lifting here. Dial in the spot with the light guide for black knight butterfly bush and get the feeding right with the black knight butterfly bush fertilising schedule — the wrong feed (too much nitrogen) is one of the most common silent reasons a healthy plant makes leaves instead of flowers.

Bloom season and what to expect

Black Knight Butterfly Bush flowers across its growing season (mostly summer) and, kept fed and deadheaded, can bloom for many weeks or right up to frost.

Post-bloom care so it flowers again

Deadhead, keep feeding lightly, and many will rebloom; collect seed from the best plants at the end of the season if you want to grow them again.

For everything else this plant needs day to day, see the full black knight butterfly bush care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Black Knight Butterfly Bush blooming — frequently asked questions

Why won't my black knight butterfly bush flower?

Black Knight Butterfly Bush blooms on the season's growth given enough sun, warmth and the right feed — there is no cold or photoperiod trick, just good growing conditions and a bloom-leaning feed. The most common reason it is not happening: Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.

How do I make black knight butterfly bush bloom?

Give black knight butterfly bush the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.

When does black knight butterfly bush normally bloom?