How to Grow Delphinium elatum from Seed

Delphinium elatum is a short-lived herbaceous perennial that forms a clump of deeply dissected, soft-green palmate foliage, from which emerge flowering stems from June to September, and is much visited by foraging insects. They are the true stars of the early summer garden!

Plants form low mounds of deeply-cut green leaves, bearing tall spikes of satiny flowers. The flowers are single or semi-double, cupped and arranged on large, upright spikes. The plant grows from a woody rhizome that sinks vertically into the ground. Its deciduous vegetation is absent in winter.

Delphiniums thrive in sunny areas with rich and deep soil, and are equally at home in window boxes, flowering pots around the house or in bouquets.

They are a good companion for mossy or gallic roses, with which they form charming tableaux in the purest English style. You can also plant them with daylilies, phlox and gypsophila or foxglove, tall bearded iris and peony.

The Basics

Height at maturity: 90-100 cm
Spread at maturity: (38 - 46cm)
Light needs: Full sun to part shade; at least six hours of sun per day
Hardiness: USDA Zones 3-7; until -40.0°C
Type of soil: Rich, fertile, well-draining, humus, loamy
Soil pH: 5.5-6.5
Water: Keep soil moist but not soaked
Where to plant: Borders, beds, containers, windowboxes
Features: Attracts hummingbirds, excellent cut flower
Pruning: Deadhead by cutting spent flower spikes back. This will encourage further blooms. Cut down all growth to ground level once it has withered in autumn.
Disease: Plants are often attacked by mildew in mid summer; simply cut back hard to encourage fresh foliage.
Flowering period: Spring to Summer
Best time to sow seeds: Spring or fall
Common names: Candle larkspur
Plant type: Short-lived perennial (2-3 years)
Difficulty: Easy; low maintenance
Warning: harmful if eaten

How to Grow Delphinium From Seed

Use a well-drained soil medium with low soluble salt levels, 10-30% clay and 0-15 % parts (e.g. bark, sand, perlite). Do not add peat to the soil. Moisten before sowing the seed.

Place seeds on top, then cover lightly with vermiculite, sand or substrate after sowing (no more than two millimeters). Keep soil slightly moist but not wet. Bottom watering is best as not to disturb the seed.

Light is not necessary until germination occurrs. Germination takes about 12-20 days at 15-22 °C.

Autumn sown seed can be overwintered in a cold frame with a frost-protecting fleece and given a permanent place in the garden the following spring. Don't let the temperatures dip below 3 °C.

Transplant into larger cell packs or 3-4" containers 6-8 weeks after germination. Support, such as a horizontal trellis is advised for larer varieties (not necessary for the Magic Fountains variety). Grow seedlings at 18-21°C in the greenhouse or cold frames. Harden off and transplant outside after the last frost.

In spring, the plants will grow best outside at 15-18°C.

The trick in hot-weather sowing is to keep the seed box dark and cool until germination, and then gradually to admit light and air. Keep soil moist but never wet. When three true leaves show, transplant to a shaded coldframe for winter.

Direct seeding in the ground outside is not recommended.

Growing on

After another 4-6 weeks, transplant each plant into its own 8-10 cm sized pot. After 4-6 more weeks, move it into a 5-10 litre-sized container.

Make sure the pots are not too small as this will inhibit root growth and thus prevent flowering.

Delphinium takes about 18-22 weeks to mature from seed. Cut back after flowering to allow it to rebloom.

Fertilization

Delphinium elatum is a heavy eater. Use a slow release, complete balanced fertilizer once per week at low concentrations. It is better to fertilize more frequently (weekly) with low concentrations. Avoid using high concentrations as roots are very sensitive to high salt levels in substrates. Avoid high ammonium and high nitrogen levels.

Don’t fertilize after flowering or after early September.