Caring for Delphinium

Delphiniums are high-maintenance perennials that reward effort with spectacular blooms but will sulk or fail without consistent care. Water regularly throughout the growing season, especially from April to August. They need moderate but reliable moisture—aim for a deep soak once or twice a week in dry weather rather than frequent shallow watering. Avoid wetting the foliage, as damp leaves encourage powdery mildew, the plant's most common ailment. Feed generously. In March, as growth begins, apply a balanced granular fertiliser such as Growmore or blood, fish and bone around the base of each clump. Follow up in April with a high-potash liquid feed every fortnight until buds show colour; this strengthens stems and improves flower quality. After cutting back spent blooms, give one more liquid feed to support any secondary flowering. Mulch annually in spring with well-rotted manure or compost, keeping it a few centimetres clear of the crown to prevent rot. This suppresses weeds, conserves moisture and adds nutrients. Delphiniums are fully hardy but the crown can rot in wet winters, especially on heavy soils. No special protection is needed, but ensure drainage remains good. Slugs and snails are the chief enemy, devouring young shoots in spring. Use your preferred control method—pellets, nematodes, beer traps or night patrols—from March onwards. Powdery mildew often appears in late summer, especially in dry spells or crowded plantings; improve air circulation and remove affected leaves promptly. Delphiniums are short-lived perennials, typically declining after three to five years, so plan to divide or replace clumps regularly.