Flowers & bulbs

How to Grow Sunflowers: Planting, Spacing, Care & Harvest

Quick answer

Direct-sow sunflowers after all danger of frost has passed (UMN; NC State), when soil is warm — about 50 degrees F or warmer (OSU) or ideally at least 60 degrees F (UGA). Plant about 1 inch deep. Spacing depends on height: roughly 6 inches for shorter types, 12 inches for tall, 18 to 24 inches for branching or giants.

Sunflower at a glance

PlantDirect sow: 0–2 wk after last frost
SunFull sun (UMN; UGA; OSU; NC State).
Waterlight moisture for germination, then regular water especially around flowering for tall types.
SpacingUMN: plant seeds one inch deep; spacing by height — 2–5 ft types about 6 inches apart; taller at least 1 foot; giants 2 feet; branching 18–24 inches.
Days to bloomBloom season July–Aug. (Purdue HO-80)
-3-2-1LF+1+2+3
■ Start indoors   ■ Plant out   ■ Harvest
Weeks relative to last frost (LF). Colored weeks show when our ZIP planner schedules each step.
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Updated

Field of sunflowers in bloom
Sunflowers (Helianthus annuus). Photo: USDA ARS (Bruce Fritz), Wikimedia Commons, Public domain (resized).

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

Planting timing

UMN: “Direct seed sunflowers after all danger of frost has passed.” Germination within 7 to 10 days (UMN Extension). UGA: plant several weeks after the last frost; soil ideally at least 60°F (UGA Extension). OSU: after last frost when soil is at least 50°F (OSU Extension). NC State: after last frost; not frost-tolerant (NC State). Soil-temp floor 50°F (OSU) vs 60°F (UGA) — show both. Succession every 1–3 weeks (UMN; UGA; Missouri).

Depth and spacing

UMN: plant seeds one inch deep; spacing by height — 2–5 ft types about 6 inches apart; taller at least 1 foot; giants 2 feet; branching 18–24 inches. UGA: 1 to 2 inches deep; thin to 12–15 inches. OSU: about 1 inch deep; branching 18–24 inches; single-stem as close as 4–6 inches. Sources differ — show each.

Tall types about 12 inches apart (UMN; OSU).

Sun, soil and water

Full sun (UMN; UGA; OSU; NC State). Well drained; pH about 6.0–6.8 (UMN/UGA) or 6.0–7.5 (OSU). Water: light moisture for germination, then regular water especially around flowering for tall types. No synthetic fertilizer rates; compost amendment OK (OSU). Stake giants / windy sites.

Care and harvest

Weed early; birds and deer may need exclusion. Seed harvest (UGA): when the back of the head turns from green to yellow-brown and heads nod; cut, hang warm dry ventilated, then rub seeds free. NC State: leaving seedheads feeds birds; self-seeds readily.

Pests and diseases (organic)

Slugs, snails, caterpillars, beetles (NC State). Handpick; iron phosphate bait; Btk for leaf feeders per label (UC IPM). Aphids: strong water spray; soap/oil per label (UC IPM aphids). UGA: spraying can harm beneficials and pollinators — use caution. Powdery mildew and leaf spots often on oldest leaves; spacing for air flow.

Related: organic pest control · ZIP planner

Frequently asked questions

When do I plant sunflowers?

After frost danger has passed (UMN; NC State), when soil is warm — about 50°F+ (OSU) or ideally 60°F+ (UGA).

How deep and how far apart?

About 1 inch deep (UMN; OSU; Missouri) or 1–2 inches (UGA). Spacing depends on height: roughly 6 inches for shorter types, 12 inches for tall, 18–24 inches for branching/giants.

How do I get blooms all summer?

Succession sow every 1–3 weeks or mix days-to-maturity (UMN; UGA; Missouri).

How do I save seeds before birds eat them?

Cut nodding, drying heads and cure indoors (UGA).

Sources