Delphinium belladonna bellamosum as a Cut Flower Crop

The notes below are made from observations while growing the crop commercially ourselves and observing D. b. bellamosum grown on other properties.
They are intended as a guide only and we accept no liability for their accuracy and/or effectiveness.
Soil: Should be well drained with a nutrient level similar to that required for chrysanthemums.
Planting: For optimum results plant plants 20-24 per m². Where it is not essential to harvest a full crop of first spikes, planting 12 per m² is acceptable.
Irrigation: Ground level irrigation such as row drip (4" spaced drippers) is recommended. Keep plants moist and well drained at all times.
Fertigation: Plants should be fed with every watering. Stock solution should contain a relatively high nitrogen ratio when compared to that required for other cut flower crops - e. g.
  • N P K
  • Summer 5 1 3
  • Winter 3 1 2
Pests & Diseases: The most common diseases of delphinium belladonna when grown undercover in New Zealand are phytophthora and powdery mildew. Sclerotinia rolfsii
(delphinium blight) can be a major problem if not diagnosed quickly and treated promptly and is typified by a sudden collapse of the plant, usually just prior to flowering. Small creamy brown sclerotes (1-2mm dia balls) may be seen at the base of the plant and a vivid white mycelium may be present in the surrounding soil.
Drenching plants with Terrazole at planting should prevent phytophthora establishing whilst regular sprays of a sulphur compound alternated with Phaltan will help prevent powdery mildew. If powdery mildew does become established include an eradicant e. g. systhane, or calixen. Nimrod is effective when used in conjunction with sulphur.
Mites can be a problem in hot weather but these pests really prefer other hosts. Broad mite however can cause much damage (deformed growth and flower colour blasts) but may be eradicated with the application of suitable systemic miticides.
Crop Care: Grow flowers through one layer of metal netting, raising as the crop grows. After the second flush the crop is best controlled by cutting all plants down to ground level and allowing to regrow.
(This is very rapid.) The crop can thus be staggered according to when different sections are cut back.
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Dowdeswell's Delphiniums - Wanganui, New Zealand