key growing information

How to Grow Delphinium From Seed

How to grow delphinium from seed: long lead time for transplants, cool seedling temperatures, support, greenhouse culture, soil, cutting and rebloom.

By Hensley’s Seed Co. September 3, 2026

Delphinium - Key Growing Information

Delphium stalks, ranging from deep indigo to periwinkle blue to bright white.

DAYS TO GERMINATION:

Allow 10–20 days at 65–70°F (18–21°C).

SOWING:

Transplants are recommended: start seed 10–16 weeks before planting out and cover it lightly. Plan on sturdy support. Pot seedlings up into cell packs or 3–4" pots 6–8 weeks after germination, and grow them cool, at 50–55°F (10–13°C), in a greenhouse or cold frame. Harden off and plant outside after the last frost, avoiding overhead watering. For greenhouse crops, set plugs into raised beds in August or September and install Hortonova (horizontal trellis) 12–18" above the bed. Keep the heated house below 60°F (16°C) and feed with a balanced fertilizer. Direct sowing isn't recommended.

LIGHT PREFERENCE:

Full sun to partial shade.

PLANT HEIGHT:

Depends on variety; strong support is highly recommended.

PLANT SPACING:

12–18" apart when grown as a perennial; 12" when grown as an annual.

HARDINESS ZONES:

Hardy in Zones 3–7. A short-lived perennial that usually lasts about 3 seasons.

HARVEST:

Cut when a quarter to a third of the flowers on the spike are open and put stems straight into water. Cutting plants back right after the first flush brings a second bloom in late summer and early fall.

SOIL REQUIREMENTS:

Fertile, well-drained, slightly alkaline soil rich in organic matter. Feed lightly and often with a balanced fertilizer.

USES:

A superb cut flower and a natural for perennial beds and borders.

SCIENTIFIC NAME:

Delphinium spp.ALTERNATE NAME: Candle larkspur