How to prune delphinium 'black knight'

After first flush (early–midsummer); cut back fully in autumn. Cut spent main spikes to the nearest lateral shoot with sharp secateurs. After secondary spikes fade, cut all stems to ground level. Remove all dead growth in autumn.

Deadhead after each flush; full cut-back once or twice per season. Pruning drives a second flush of the iconic dark-violet spikes. After the first flush, cut spent spikes back to the nearest lateral bud or to strong basal shoots. Once secondary spikes fade, cut all growth to the ground to stimulate fresh basal foliage. Cut back to ground level again in autumn after frost.

Cut spent main spikes to the nearest lateral shoot with sharp secateurs. After secondary spikes fade, cut all stems to ground level. Remove all dead growth in autumn.