Perennial
How to grow delphiniums
Delphinium elatum hybrids
Delphiniums need full sun, shelter from wind and deep, fertile soil that holds moisture in summer but drains in winter. Plant in March or April for flower spikes in June and July. Three jobs decide the result: keep slugs off the new shoots from February, stake before the stems reach 30 cm, and feed generously, because this is one of the hungriest border perennials. Cut back after flowering for a second, smaller show in September.
- Hardiness
- Fully hardy
- Position
- Full sun, sheltered
- Soil
- Deep, rich, moisture-retentive, free-draining
- Ideal pH
- 6.5 to 7.5
- Water
- Moderate to high in dry spells
- Feeding
- Heavy feeder
Sowing and planting delphiniums
WhenPlant Mar to Apr; flowers Jun to Jul (second flush Sep if cut back)
Starting off
Plant pot-grown crowns Mar to Apr or Sep. Sow fresh seed Feb to Mar at 15 to 18 °C, 3 mm deep, germination 14 to 28 days; old seed loses viability within a year. Named forms come from basal cuttings 8 cm long taken Mar to Apr when shoots are solid, rooted in grit at 15 °C; divide clumps in Mar every 3 to 4 years.
Spacing and planting
Plant 60 to 90 cm apart in a clump of three, or in a row 45 cm apart with 90 cm between rows; set the crown at soil level. Not a container plant beyond a 50 cm tub for dwarf 'Magic Fountain' types.
Varieties worth growing
- Pacific Hybrids 'Black Knight'
- Deep violet-blue with a dark eye, about 1.5 m, widely sold and easy from seed. Shorter-lived than named cutting-raised plants, so expect to replace it every few years.
- Magic Fountains Series
- Dwarf at about 90 cm with full-sized spikes. Needs little staking and is the one to choose for a windy garden or a large tub.
- New Millennium Series 'Pagan Purples'
- Modern seed strain with thick, strong stems and double purple flowers; stands up to weather and mildew better than the Pacific Hybrids.
- D. elatum 'Faust'
- Named variety raised from cuttings, tall at up to 2 m, in ultramarine with a dark eye. Long-lived if divided, for the back of a sheltered border.
- Belladonna Group 'Völkerfrieden'
- Branching plant about 1 m tall with loose sprays of gentian blue instead of one heavy spike. Lighter in the border, good for cutting and repeat flowers readily.
Delphiniums month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Clear dead leaves from the crowns and top up the ring of grit.
- February
Start slug patrols as the first shoots show. Sow fresh seed indoors at 15 to 18 °C.
- March
Plant, or divide old clumps. First feed and a mulch. Take basal cuttings.
- April
Thin established clumps to the strongest 5 to 7 shoots. Stake when growth reaches 30 cm.
- May
Second, lighter feed. Tie in every 30 cm. Start potash liquid feeds as the spikes form. Water in dry spells.
- June
Flowering. Keep tying in and watering.
- July
Cut spent spikes down, feed and water well for a second flush.
- August
Keep the regrowth watered. Remove mildewed leaves.
- September
Second flush flowers. Pot-grown plants can go in this month.
- October
Nothing to do beyond clearing fallen leaves from around the crowns.
- November
Cut all stems to the ground and ring the crown with grit.
- December
Nothing to do.
Feeding delphiniums
A hungry plant: tall spikes built in ten weeks need a balanced feed in spring, potassium as the spikes form and another feed after cutting back. Rich soil and a mulch matter as much as the fertiliser.
Hungry for those tall spires, rich soil and a balanced spring feed; mulch well.
Feeding plan
March, as shoots emerge
100 g/m² scattered round the clump and lightly forked in; a group of three plants covers about a square metre, so roughly 35 g each. Follow with a 5 cm mulch of garden compost, kept off the crown.
Mid May to late June, as spikes form and colour
Potassium Rich Fertiliser 11% K
1 g per litre of water (10 g in a 10 litre can) every 2 weeks, about 5 litres to each established clump.
July, after cutting back the spent spikes
50 g/m² watered in thoroughly, to fuel the September flush. Nothing after this.
Potting, dwarf varieties in tubs
5 g per litre of compost mixed in: 250 g for a 50 cm tub holding about 50 litres. Top-dress at 2 g per litre (100 g) in May.
Signs to watch
Floppy spikes with pale, large leaves
Nitrogen excess and shade
High-potash feed and full sun
Lower leaves yellow with brown edges in Jul
Potash short
Sulphate of potash
Small, late spikes on an old clump
Congestion
Divide in Mar and replant in soil enriched with compost
Pests, diseases and problems
Shoots fail to appear in spring, or come up chewed and hollowed at the base
Slugs and snails feeding on the crown and new shoots from late winter, the most common cause of lost delphiniums
Clear old debris from the crown in January, ring it with sharp grit, and hand-pick at night from February. Apply nematodes as soon as the soil reaches 5 °C and again six weeks later.
White powdery coating on leaves and stems from midsummer
Powdery mildew, worst on crowded clumps that are dry at the root
Thin shoots in April, water deeply in dry spells and mulch. Cutting the plant back after flowering removes most of it; clear and bin the foliage in autumn.
Large, irregular black blotches on the leaves, spreading to stems and flower buds
Delphinium black blotch, a bacterial disease splashed up from the soil in wet weather
Remove affected leaves as soon as they appear and avoid overhead watering. Dig up and bin plants that are badly affected, and do not replant delphiniums in the same place.
Leaves with brown, dried patches towards the tips, containing small grubs
Delphinium leaf miner
Pick off and bin mined leaves. The damage is unsightly but does not stop flowering.
Flower buds and young leaves eaten, with caterpillars hidden in the spike in June and July
Caterpillars of the golden plusia and other moths
Search the spikes and remove caterpillars by hand.
Crown is brown and rotten in spring and no shoots grow
Crown rot after a winter in wet, heavy soil
Improve drainage before replanting, set the crown at soil level, never deeper, and keep mulch off it. On clay, plant on a slight mound.
Pruning
Pruning and care
Thin a mature clump to 5 to 7 of the strongest shoots in Apr. Stake each spike with a 1.5 m cane at 30 cm tall, tying every 30 cm, or set a grow-through grid by May. Cut spent spikes to the ground and feed for a Sep second flush; cut to the ground in Nov and ring the crown with grit.
Good to knowStake early against wind; thin shoots for stronger spikes.
Growing delphiniums in pots
Tall delphiniums are not container plants: the roots run deep, the spikes catch the wind and the pot dries out in hours. Dwarf strains such as the Magic Fountains Series will grow in a tub at least 50 cm across and deep, one plant to a tub, in loam-based compost with the 4-4-4 mixed through. Water daily in summer, stand the tub out of the wind and still put in a cane. Raise it on feet in winter so the crown does not sit wet, and expect to replace or replant into the border after two or three years.
Delphiniums: common questions
Do delphiniums come back every year?
Yes, delphiniums are hardy perennials that die down in autumn and regrow each spring. They are not always long-lived, though: seed-raised strains often fade after three or four years, and any delphinium can be lost to slugs eating the shoots or to winter wet rotting the crown. Dividing or taking basal cuttings every three to four years keeps them going.
Are delphiniums poisonous to dogs and cats?
Yes, all parts of a delphinium are poisonous if eaten, to dogs, cats, horses and people. Plant them away from pets that chew plants, and contact a vet if any is eaten. The sap can irritate skin, so wear gloves when cutting back or taking cuttings.
When should I cut back delphiniums?
Cut back twice: once after the first flowering in July, and again in November. In July, cut each finished spike down to ground level, then feed and water, and new shoots flower in September. In November, cut every stem to the ground and clear the debris so slugs have nowhere to overwinter.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.