Getting it to bloom

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

Also called Black Knight delphinium (Delphinium elatum 'Black Knight').

More about delphinium 'black knight'

About Delphinium 'Black Knight'

Delphinium elatum 'Black Knight' · also called Black Knight delphinium · flowering

'Black Knight' is a Pacific Giant (Round Table) Delphinium elatum hybrid with towering spires of deep velvety violet-purple flowers, each with a dark bee, in early summer. A stately back-of-border perennial reaching 1.5-1.8 m, it needs full sun, rich moist soil, shelter and staking. All delphiniums are toxic to cats and dogs.

Plant type: flowering

Watch for — Wind and rain damage: Tall spikes snap in exposure. Plant in a sheltered spot and stake each stem early with canes or grow-through supports before the flowers add weight.

The reasons delphinium 'black knight' isn't blooming

Almost every non-blooming delphinium 'black knight' 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 delphinium 'black knight' 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 delphinium 'black knight' to flower

Maximise sun. Give delphinium 'black knight' 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 delphinium 'black knight' and get the feeding right with the delphinium 'black knight' 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

Delphinium 'Black Knight' 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 delphinium 'black knight' care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Delphinium 'Black Knight' blooming — frequently asked questions

Why won't my delphinium 'black knight' flower?

Delphinium 'Black Knight' 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 delphinium 'black knight' bloom?

Give delphinium 'black knight' 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 delphinium 'black knight' normally bloom?