How to Grow Delphiniums from Seed (Delphinium elatum)

Few flowers say ‘summer border’ like a delphinium: tall spires of blue, violet, white or pink standing over everything else in June. Bought as plants they are expensive, and named varieties are short-lived, so the sensible way to fill a border with them is from seed. Growing delphiniums from seed is not hard once you know their one quirk — the seed wants it cool and dark, not warm and bright like most flowers. This guide covers Delphinium elatum and its hybrids, from sowing in late winter to staking, slug control and getting a second flush of flowers in September, with a side-by-side look at their annual cousin, larkspur.

• Sow January–March under cover, or fresh seed in July–August
• Germination 2–4 weeks at 13–18 °C · cover the seed and keep it dark
• Plant out April–May, 45–60 cm apart, full sun, rich but free-draining soil
• Flowers June–July, with a second flush in September if cut back

Which delphiniums can you grow from seed?

Garden delphiniums are hardy herbaceous perennials: they die back to a crown each autumn and push up fresh shoots in spring. The big border types belong to the Delphinium elatum group, and the best-known strain raised from seed is the Pacific Giants (sold as Delphinium × cultorum) — spikes of 1.5–1.8 m in mixed blues, purples, pinks and whites, many with a contrasting central ‘bee’. They are not as long-lived as the old named clones, typically giving three or four good years, which is exactly why a fresh sowing every couple of years makes sense.

From seed you can also grow the lighter, branching Belladonna types, around 90–120 cm and excellent for cutting, the compact gentian-blue Delphinium grandiflorum 'Summer Blues', which often flowers in its first summer, and the unusual orange-red Delphinium nudicaule from California, a short plant for very well-drained soil or pots. You will find all of them in our delphinium seed collection, and the annual species in larkspur.

When to sow delphinium seeds

There are two good windows. The main one is January to March, in an unheated greenhouse, cold frame or cool windowsill. Plants sown in January or February often give a modest first show in late summer and flower properly the following June. The second window is July to August, using freshly harvested seed; the seedlings are potted on, overwintered in a cold frame and planted out in spring. Delphinium seed is short-lived — our guide to how long seeds last puts it at one to two years — so buy fresh and keep any leftovers in a sealed jar in the fridge.

A third, low-effort route is to sow outdoors in winter and let the weather do the chilling. Delphiniums respond well to a cold spell before germination, which makes them ideal for winter sowing in milk jugs from December to February. For the science behind that, see how to grow perennials from seed.

How to sow delphiniums: cool and dark

• Chill the seed first. A week or two in the fridge, in its packet inside a sealed bag, evens out germination — especially for seed that is a few months old.
• Sow thinly and cover. Use a gritty seed compost, sow on the surface and cover with about 3 mm of sieved compost or vermiculite.
• Exclude light. Delphinium seed germinates better in darkness. Cover the tray with a sheet of cardboard or newspaper and check daily.
• Keep it cool. 13–18 °C is ideal. Above about 20 °C germination drops sharply, so a heated propagator or a warm kitchen does more harm than good.
• Uncover as soon as they show. Remove the cover the moment the first seedlings appear and give them good light so they stay short.

Seedlings usually appear in two to four weeks. If nothing happens, the usual culprit is heat; our guide to why seeds are not germinating covers the rest.

Pricking out, planting and staking

Prick the seedlings out into individual 9 cm pots once they have their first true leaves, and grow them on somewhere cool and bright. Harden them off and plant out from April into May, in full sun, sheltered from strong wind, in fertile soil that holds moisture in summer but never sits wet in winter — waterlogged crowns rot. Space tall types 60 cm apart and Belladonnas around 45 cm, and dig in plenty of compost first.

Stake early. When the shoots of Pacific Giants reach 30–45 cm, push in a cane for each flowering stem and tie loosely as they grow, or surround the clump with canes and string. A single summer storm can snap an unsupported spike at the base. Our guide to plant supports shows the options.

How to grow delphiniums from seed: step by step

1. January–March: chill, sow and cover One to two weeks in the fridge, then sow under 3 mm of compost at 13–18 °C, in the dark.
2. After 2–4 weeks: uncover and give light Remove the cover as soon as seedlings appear; keep cool to avoid leggy growth.
3. First true leaves: pot on One seedling per 9 cm pot in a cool greenhouse or cold frame.
4. April–May: harden off and plant Full sun, rich free-draining soil, 45–60 cm apart; protect from slugs straight away.
5. At 30–45 cm: stake each spike Canes and soft ties now save broken stems later.
6. After flowering: cut back and feed Cut spent stems to the ground, water and feed for a second flush in September.

Delphinium or larkspur?

The two are close relatives and are often mixed up on seed packets — larkspur is sold as Consolida ajacis, Delphinium consolida or Delphinium ajacis. The difference that matters in the garden is lifespan and how you sow them:

Larkspur germinates best in cool soil, which is why it features in our guide to autumn-sown hardy annuals. Hang bunches upside down when the lower third of the florets are open and they keep their colour for months, alongside strawflowers and statice. Browse the annual forms in Delphinium consolida.

Common mistakes when growing delphiniums

• Germinating them warm. A propagator at 21 °C plus is the most common reason delphinium seed fails. Keep it cool.
• Using old seed. Viability drops quickly at room temperature. Sow fresh seed, or store it in the fridge.
• Ignoring slugs in spring. Young shoots in March and April are a slug favourite and a crown can be grazed to nothing overnight — see common garden pests.
• Staking too late. Once a spike has bent or snapped it will not recover. Put supports in when shoots are knee-high.
• Crowding. Poor airflow invites powdery mildew in late summer. Give each plant room and water at the base — more in common plant diseases.
• Forgetting they are toxic. All parts, the seed above all, are poisonous if eaten. Wear gloves and keep seed away from children and pets.

Frequently asked questions

Do delphiniums flower in the first year from seed?
Some do. Pacific Giants and 'Summer Blues' sown in January or February often flower in late summer of the same year, but the full display comes in the second June. Summer-sown seedlings flower the following year.

Do delphinium seeds need cold stratification?
Fresh seed germinates without it, but a week or two in the fridge improves and evens out germination, especially for stored seed. Winter sowing outdoors gives the same chilling naturally.

How long do delphiniums live?
Seed-raised strains such as Pacific Giants usually give three to four good years before declining. Sow a small batch every couple of years to keep the border full.

Can I get a second flush of flowers?
Yes. Cut the faded spikes down to the ground straight after the first flowering in July, then water and feed. New, shorter spikes usually appear in September.

A tray of delphiniums sown this winter fills a border for years for the price of a single potted plant. Pair them with foxgloves, columbines and echinacea for a cottage-garden mix that bees love, or browse more perennial flower seeds and blue flowers. New to sowing? Start with our beginner's guide to growing flowers from seed, browse all our seed collections, or explore the rest of our growing guides.