Flowers & bulbs

How to Grow Delphinium: Planting, Care & Toxicity

Quick answer

Start indoors 2–4 weeks before last frost (NDSU H1139). Transplant 4–6 weeks after last frost. NC State: medium severity poison — flowers, leaves, stems; alkaloids; contact dermatitis yes. Digestive issues if ingested. Stake tall types; full sun and excellent drainage.

Delphinium at a glance

PlantStart indoors: 4–2 wk before last frost; Transplant: 4–6 wk after last frost
SunFull sun (≥6 hours); high organic matter; good drainage; alkaline soil listed (NC State).
SpacingNC State: available space about 12 inches–3 feet and 3–6 feet for taller types; width about 2–3 ft; height classes from about 3–5 ft short to over 6 ft tall.
Days to bloomBlooms in summer (NC State)
-5-4-3-2-1LF+1+2+3+4+5+6+7
■ Start indoors   ■ Plant out   ■ Harvest
Weeks relative to last frost (LF). Colored weeks show when our ZIP planner schedules each step.
Jump to

Updated

Poison (required): NC State rates Delphinium elatum poison severity Medium. Toxic principle: alkaloids. Poison parts: flowers, leaves, stems. Symptoms: digestive issues. Causes contact dermatitis: yes. Keep away from children and pets; do not ingest; wash after handling. This page is not medical advice. (NC State Delphinium elatum)

Blue Delphinium elatum spikes
Delphinium (Delphinium elatum). Photo: Krzysztof Ziarnek, Kenraiz, Wikimedia Commons, CC BY-SA 4.0 (resized).

Sourced from university extension guides. For dates where you live, use the ZIP planting planner.

Planting timing

NDSU H1139 chart header: sowing date = number of weeks before last frost date. Delphinium: sow 2 to 4 weeks (2–4 weeks); transplant 4–6 weeks after last frost. That sets planner Start indoors last frost −4 to −2 and Transplant last frost +4 to +6. (NDSU H1139)

Size and staking

NC State: available space about 12 inches–3 feet and 3–6 feet for taller types; width about 2–3 ft; height classes from about 3–5 ft short to over 6 ft tall. Staking is necessary. Plant along a fence for wind and rain protection; afternoon shade helps in southernmost zones. (NC State)

Sun, soil and water

Full sun (≥6 hours); high organic matter; good drainage; alkaline soil listed (NC State). High humidity is detrimental. Good drainage and air circulation reduce disease. Prefer compost in spring; we omit printed synthetic fertilizer rates.

Toxicity

NC State: poison severity Medium; alkaloids; poison parts flowers, leaves, stems; digestive issues; contact dermatitis yes. (NC State)

Pests and diseases

NC State diseases: crown rot, leaf spot, blight, powdery mildew — sunny site, drainage, air flow. Pests: snails/slugs, aphids, leaf miners, mites, stem borers. Slugs: handpick; iron phosphate as the label directs (UC IPM). Aphids: soap or oil with thorough coverage (UC IPM aphids).

Related: ZIP planner · foxglove · organic pest control

Frequently asked questions

When do I transplant delphinium?

About 4–6 weeks after last frost (NDSU). Start indoors −4 to −2.

Is delphinium poisonous?

Yes — NC State medium severity. Flowers, leaves, and stems; alkaloids; contact dermatitis. Do not ingest.

Do I need to stake them?

Yes for taller types (NC State).

Sources