Perennial
Delphinium
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Flowers | Flowers in June | Flowers in July | Flowers in September | |||||||||
| Plant | Plant in March | Plant in April | Plant in May | |||||||||
| Prune | Prune in July | Prune in August | ||||||||||
| Looks good | Looks good in June | Looks good in July |
Overview
Few plants say cottage garden like a row of delphinium spires in true blue. The tall Elatum hybrids reach well over head height in good soil, with flowers in shades of blue, mauve, pink and white, each with a contrasting central "bee". For less staking, try the Belladonna group, which is shorter and more branched, or the compact New Millennium and Magic Fountains series.
Where to grow delphinium
Grow them in full sun in rich, deep soil that stays moist in summer but does not lie wet in winter. Shelter from strong wind matters, because hollow stems snap easily. They do best in cooler, wetter summers, so gardens in the north and west often grow them better than hot, dry eastern ones.
Planting
Plant young plants in spring once the worst frosts have passed, spacing them 45–60 cm apart. Improve the soil with well-rotted manure or compost first. Avoid burying the crown, which can rot.
Care through the year
Spring
Protect emerging shoots from slugs, then thin strong clumps to five to seven stems. Insert canes or grow-through supports before shoots reach 30 cm.
Summer
Tie stems in as they grow, water deeply in dry spells and feed with a balanced liquid fertiliser every couple of weeks until flowering.
Autumn
Enjoy any second spikes, then cut stems to the ground once they die back.
Winter
Mark where clumps sit so you do not dig into them; spread coarse grit around crowns on heavy soil.
Pruning
Once the main spikes fade in July, cut them back to just above the healthy leaves. New shoots will usually produce shorter spikes in September. Cut everything to the base in autumn.
Propagation
Take basal cuttings in spring: slice off young shoots about 8–10 cm long with a sliver of the woody crown attached, and root them in gritty compost. Seed is cheap but variable; Pacific Giants come reasonably true.
Common problems
Slugs and snails are the biggest threat, often wiping out young shoots overnight. Powdery mildew appears in late summer; good air flow and watering help. Crown rot strikes on waterlogged soils.
Guides to the problems most likely to affect delphinium:
Something else wrong? Diagnose it by symptom.
Month-by-month reminders
Jobs for this plant come round in March, April, May, July and August. Each month page lists everything else worth doing in the garden at the same time.
Related plants
Sources
Botanical names follow Kew's Plants of the World Online; growing attributes were checked against the references below. Text is our own. See our editorial policy.