Delphiniums produce the most extraordinary vertical element in the cutting garden — tall spikes packed with flowers in true blue, purple, white, and bicolors, sometimes scented, irresistible to bees and impossible to substitute. They are also among the more demanding garden plants: they want rich, deep, moisture-retentive soil, staking before the stems reach their full height, and protection from wind.
Cut the main spike when the lower third of flowers is open. After the first flush, cut back to lateral shoots which will produce a second, smaller flush. In Zone 6b they are reliably perennial with good drainage. All parts are toxic — wear gloves when handling.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Botrytis (grey mould)
Grey fuzzy mould on petals and stems, worst in cool wet conditions.
Remove affected parts immediately. Improve air circulation. Avoid overhead watering. Apply copper fungicide if severe.