Delphinium

Sun

Full sun; light afternoon shade can help in warmer areas. Choose a position sheltered from strong winds.

Water

Keep the root zone evenly moist during growth and flowering, watering deeply during dry spells. Avoid waterlogged soil, especially in winter.

Soil

Fertile, humus-rich, well-drained soil, preferably neutral to slightly alkaline. Improve heavy soil drainage before planting.

Height

4-6 ft (1.2-1.8 m), occasionally reaching 8 ft (2.4 m)

Spread

2-3 ft (0.6-0.9 m)

Flowers

Early to midsummer, sometimes with a smaller late-summer flush after cutting back. The species has blue to violet flowers, often with contrasting dark centres; cultivated selections and related hybrids offer a wider colour range.

Foliage

Green, deeply palmately lobed leaves form a basal clump, with smaller leaves along the flowering stems. Top growth dies back in winter.

Growth

Fast seasonal growth from a dormant crown.

Care needed

High

• Water deeply during dry weather; do not let the soil dry out while flower spikes are developing.
• Top-dress with compost and apply a balanced fertiliser as growth starts in spring.
• Mulch to retain moisture, keeping mulch clear of the crown.
• Install tall stakes or a support frame early, and tie stems loosely as they lengthen.
• Divide congested clumps in early spring, usually every three to four years if growth weakens.

Pruning. Cut spent flower stems back to healthy basal growth after the first flush to encourage a smaller repeat display. Once the foliage dies back in autumn, cut the remaining stems close to ground level and remove diseased debris.

Early spring

Divide congested clumps as new shoots appear, and protect emerging growth from slugs and snails.

Spring

Apply compost and balanced fertiliser, then install supports before stems become tall.

Late spring

Tie developing stems to supports and water deeply if rainfall is insufficient.

Early summer

Check ties as flower spikes lengthen, and watch for aphids and powdery mildew.

Midsummer

Cut back spent flowering stems; water and give a light feed if the plant is making fresh growth.

Late autumn

Remove dead top growth and check that water is not collecting around the crown.

• Plant near the back of a sunny mixed border for tall flower spires above lower perennials.
• Combine with roses, peonies and hardy geraniums for a layered cottage-garden border.
• Repeat small groups along a long border to create rhythm and vertical accents.
• Use blue-flowered forms with white flowers and silver foliage for a cool summer colour scheme.

Garden styles it suits: English country, Cottage garden, Romantic rose garden, Arts and Crafts, Blues and silvers and English manor.

Plant it with: Roses, Peonies, Hardy geraniums, Catmint, Lady's mantle and Border phlox.

Wildlife: Flowers provide nectar and pollen for bees, especially bumblebees. Double-flowered selections may offer less accessible food than single flowers.

• Slugs and snails can destroy emerging shoots: inspect new growth frequently, remove pests and use iron-phosphate bait according to the label where needed.
• Powdery mildew causes white-coated leaves: allow good air circulation, water the soil rather than the foliage and prevent drought stress.
• Crown and root rot cause wilting or collapse in wet soil: improve drainage, keep mulch off the crown and remove badly affected plants.
• Flower stems snap or lodge in wind and rain: provide sturdy supports early and tie individual stems loosely at several heights.

All parts are poisonous to people, cats, dogs and horses if eaten, especially seeds and young growth. Delphinium alkaloids can cause severe weakness, heart effects, breathing failure and death. Keep plants and cuttings away from grazing animals and seek urgent medical or veterinary advice after ingestion; wear gloves if the sap irritates your skin.

• Annual larkspur (Consolida ajacis)

  Usually has much finer, threadlike leaf divisions and a lighter, more branching habit. It completes its life cycle in one season rather than returning from a perennial crown.

• Monkshood (Aconitum napellus)

  Has similar divided foliage and blue flower spikes, but each flower has a rounded helmet-shaped hood rather than a backward-pointing delphinium spur. Monkshood is also highly poisonous.

• Foxglove (Digitalis purpurea)

  Has broad, softly hairy leaves and hanging tubular bells, often arranged along one side of the stem. Delphinium has divided leaves and open-faced, spurred flowers.

Delphinium comes from the Greek word for dolphin, referring to the shape of the flower buds, while elatum means tall.

Propagation. Sow fresh seed, following the supplier's instructions because germination requirements vary; a period of cold can help. Named selections may not come true from seed, so propagate them by basal cuttings in spring or careful division of healthy clumps.

Accepted botanical name

Delphinium elatum

In the US and Canada

Introduced in Alaska, Canada and the lower 48 states.

Native range

Altay, Austria, Belarus, Central European Rus, Czechoslovakia, East European Russia, France, Irkutsk, Kazakhstan, Kirgizstan, Krasnoyarsk and Mongolia.

Measured

Soil pH 7 to 7.5. Average height 163 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.