Delphinium in April: monthly care

Delphiniums thrive in full sun and demand well-drained, fertile soil. They perform best in loam or chalky soils with a neutral to slightly alkaline pH. Before planting, dig over the bed to at least a spade's depth and incorporate plenty of well-rotted manure or garden compost, along with a handful of bonemeal per square metre. Good drainage is essential; delphiniums will rot in waterlogged ground, so avoid heavy clay unless you improve it significantly with grit and organic matter. Plant young delphiniums in March, April or May for flowering the same summer, or in September and October for establishment before winter. Space plants 45 cm apart to allow air circulation and reduce mildew risk. Dig a hole slightly larger than the root ball, set the crown at soil level—never deeper—and firm in gently. Water thoroughly after planting to settle the roots. Delphiniums grow tall and their hollow stems are notoriously brittle, so staking is non-negotiable. Insert sturdy canes or a grow-through support at planting time, before the stems elongate, to avoid root damage later. As shoots emerge, tie them loosely to canes with soft twine every 30 cm or so. Apply a 5 cm mulch of compost or well-rotted manure around the base after planting, keeping it clear of the crown to prevent rot. Water regularly during the first season to help roots establish, especially in dry spells. Delphiniums are hungry, thirsty plants, so starting them off in rich, well-prepared soil makes all the difference to their performance.

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.