Garden PlannerEvidence-aware. Garden with confidence.
Entire healthy mature sunflower plant in a real garden bed, showing growth habit and scale.Primary identification image. 150–300 cm tall, 45–60 cm wide at maturity.

Sunflower

Helianthus annuus L.

Family
Asteraceae
Season
Warm-season annual
Best grown in
Portland, Oregon

A very tall annual that casts heavy shade and feeds bees, then birds; plan for its footprint and shadow.

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Life cycle & growth stages

  1. 1. SeedSow 2–3 cm deep after frost.
  2. 2. SeedlingEmerges in 7–10 days; protect from slugs.
  3. 3. Mid-growthRapid height gain; stake if exposed.
  4. 4. FloweringHeads open at 8–12 weeks; bees visit.
  5. 5. SeedHeads droop; seeds ripen.
  6. 6. HarvestCut heads and dry, or leave for birds.

Growth stages are ordered chronologically; timing varies with cultivar, temperature, light and care.

Planting calendar for Portland, Oregon

direct sow 1–5 weeks after last frost; 70–100 days to maturity from sowing. Windows are derived from the region's average frost dates (last Apr 5, first Nov 5) and are estimates until you confirm your own dates in the calendar.

SunflowerHelianthus annuus
PlantStart indoorsDirect sowAutumn sowTransplantTendHarvest
Sunflower—Apr 12–May 10 (estimate)——May 10–Jun 21 (estimate)Jun 21–Sep 1 (estimate)
  • Direct sow: Apr 12 – May 10
  • Tend and monitor: May 10 – Jun 21
  • Harvest: Jun 21 – Sep 1

Spacing & support

In-row 30–60 cm; rows 75–90 cm. Planner footprint: 1 cell of 30 cm.

Side-profile diagram of mature sunflower: canopy 150–300 cm tall, 45–60 cm wide, deep root zone, support and harvest-access envelope.

Soil & water

Soil
Any well-drained soil
pH
6–7.5
Fertility
moderate
Water
Deep water weekly in dry weather.
Frost
tender; killed by frost

Support & training

Stake tall cultivars in wind. Install at planting so roots are not disturbed later.

Sunflower trained on its support: stake tall cultivars in wind.

Harvest signs

  • Back of the head turns yellow-brown
  • Petals drop; seeds plump
  • Cover heads with mesh against birds
Sunflower at harvest readiness, showing the visual cues: back of the head turns yellow-brown; petals drop; seeds plump.

Common problems

Pests: birds, squirrels, slugs on seedlings

Diseases: rust, downy mildew

Appearance alone is not a diagnosis; confirm with a regional extension guide.

Side-by-side: healthy sunflower leaf or fruit and an example of rust.

Container growing

  • Minimum 20 L (30 cm deep)
  • Use quality potting mix and water more frequently
  • Dwarf cultivars only.
Mature sunflower in a correctly sized container (20 L or more) with drainage visible.

Companion overview

3 reviewed relationship records (evidence: low).

Supported or conditional

None reviewed

Avoid or separate

None with evidence

Traditional claims only: Cucumber, Pole beans, Potato.

Full companion profile

Crop rotation

Avoid planting sunflower or other daisy family crops in the same spot for 1 year. Rotation is about previous seasons, not about live neighbours.

Year 1Year 2Year 3AsteraceaeOther familyOther familyback after 1+ years

Shared risks in Asteraceae: lettuce downy mildew, aphids, slugs on lettuce.

Crop rotation hub

Sources, reviewer & update

Sources

Reviewer: Garden Planner editorial team (pending independent horticultural review)

Last reviewed: August 15, 2026 · version 1

Found an error or have feedback? Let us know.

Growing sunflower

Sunflowers are sown directly after the last frost and reach 1.5–3 m in 70–100 days. Their shade to the north is substantial, which can shelter lettuce in summer or rob sun from peppers. Seed heads feed birds in autumn if left.

Sunflower seed beside a ruler or coin for scale.
Sunflower seedling at cotyledon and first-true-leaf stage, in soil, distinguishable from common weeds.
Immature seeds of sunflower developing on the plant.

Sunflowers are commonly said to be allelopathic; laboratory bioassays show inhibitory compounds in hulls and residues, but a field effect on garden neighbours at normal spacing is not established, and competition for light and water explains most observations. Their large flowers are heavily visited by bees.

Two or more mature sunflower plants with a tape measure showing in-row spacing (30–60 cm).
Sunflower flower detail or bolting stage.
Immature seeds of sunflower developing on the plant.

Edible parts and safety

Edible: seeds, petals, buds.

Hands or tool harvesting sunflower correctly (cut, pull, twist or pick) without damaging the plant.

Pests and diseases

Common pests: birds, squirrels, slugs on seedlings. Common diseases: rust, downy mildew. These vary by region; a photograph is an example, not a diagnosis. See the pest and disease guides and your local extension service.

birds on sunflower, with a wider damage-context view.

Timeline

Season timeline for sunflower: sowing, transplanting, flowering, harvest and bed occupancy aligned to frost dates.Text alternative: Direct sow Apr 12–May 10; Tend and monitor May 10–Jun 21; Harvest Jun 21–Sep 1.

Related plants

See also: Asteraceae family page · crop rotation · regional calendar · guides

Our Methodology & Sources

We synthesize peer-reviewed research, university extension publications, and trusted horticulture resources. Our evidence levels help you understand how strong the science is behind the guidance.

Evidence tiers

Supported evidenceConsistent results from multiple robust studies
Traditional claimHistorical use reported, limited scientific support
Context dependentMixed or variable results across conditions
No verified relationshipNo reliable evidence identified

Primary source types

  • Peer-reviewed journal articles
  • University extension publications
  • Government & research institute reports
  • Systematic reviews & meta-analyses

Last updated

August 24, 2026

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