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Entire healthy mature corn plant in a real garden bed, showing growth habit and scale.Primary identification image. 150–250 cm tall, 30–45 cm wide at maturity.

Corn

Zea mays L.

Also called: Sweet corn, Maize, Sweetcorn

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

A tall, wind-pollinated, heavy-feeding grass that must be planted in blocks, not single rows, to fill its ears.

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Life cycle & growth stages

  1. 1. SeedSow 3–4 cm deep in blocks.
  2. 2. SeedlingEmerges in 7–10 days.
  3. 3. Mid-growthRapid growth; hill soil around the base.
  4. 4. TassellingTassels shed pollen onto silks.
  5. 5. Ear fillKernels fill over 3 weeks after silking.
  6. 6. Harvest readySilks brown; kernels milky.
  7. 7. HarvestTwist ears downward; eat quickly.

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

Planting calendar for Portland, Oregon

direct sow 1–4 weeks after last frost; 65–95 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.

CornZea mays
PlantStart indoorsDirect sowAutumn sowTransplantTendHarvest
Corn—Apr 12–May 3 (estimate)——May 3–Jun 16 (estimate)Jun 16–Aug 20 (estimate)
  • Direct sow: Apr 12 – May 3
  • Tend and monitor: May 3 – Jun 16
  • Harvest: Jun 16 – Aug 20

Spacing & support

In-row 20–30 cm; rows 75–90 cm. Planner footprint: 1 cell of 30 cm.

Side-profile diagram of mature corn: canopy 150–250 cm tall, 30–45 cm wide, deep root zone, support and harvest-access envelope.

Soil & water

Soil
Fertile, well-drained loam
pH
6–7
Fertility
high
Water
Critical during tasselling and ear fill.
Frost
tender; killed by frost

Support & training

No support structure needed.

Corn mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Harvest signs

  • Silks brown and dry
  • Ear feels full to the tip
  • Kernel exudes milky juice when pierced
Corn at harvest readiness, showing the visual cues: silks brown and dry; ear feels full to the tip.

Common problems

Pests: corn earworm (tomato fruitworm), cutworms, raccoons, birds

Diseases: corn smut, rust

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

Side-by-side: healthy corn leaf or fruit and an example of corn smut.

Container growing

Needs a block of plants for pollination; not practical in containers.

Companion overview

7 reviewed relationship records (evidence: high).

Supported or conditional

Pole beans, Winter squash, Lettuce

Avoid or separate

Tomato

2 popular pairings reviewed with no verified relationship.

Full companion profile

Crop rotation

Avoid planting corn or other grass family crops in the same spot for 2 years. Rotation is about previous seasons, not about live neighbours.

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

Shared risks in Poaceae: corn earworm (also tomato fruitworm), corn smut, raccoons and birds.

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 corn

Sweet corn is sown directly after the last frost into soil above 16 °C, in blocks of at least four short rows so the wind carries pollen from tassels to silks. Single rows produce half-filled ears.

Corn seed beside a ruler or coin for scale.
Corn seedling at cotyledon and first-true-leaf stage, in soil, distinguishable from common weeds.
Corn mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Plants reach 1.5–2.5 m and cast deep shade to the north (in the northern hemisphere); that is an asset for lettuce in summer and a problem for sun-loving neighbours. Corn is a heavy nitrogen feeder.

Two or more mature corn plants with a tape measure showing in-row spacing (20–30 cm).
Corn flower detail or bolting stage.
Immature kernels of corn developing on the plant.

Corn earworm is the same insect as tomato fruitworm (Helicoverpa zea), so adjacent tomatoes and corn share a pest; extension services advise separating them. In the Three Sisters arrangement, corn provides the physical support for pole beans.

Edible parts and safety

Edible: kernels (ears).

Hands or tool harvesting corn correctly (cut, pull, twist or pick) without damaging the plant.
Corn at end of season: seed head, dry pod, spent plant or removal stage.

Pests and diseases

Common pests: corn earworm (tomato fruitworm), cutworms, raccoons, birds. Common diseases: corn smut, rust. These vary by region; a photograph is an example, not a diagnosis. See the pest and disease guides and your local extension service.

corn earworm on corn, with a wider damage-context view.

Timeline

Season timeline for corn: sowing, transplanting, flowering, harvest and bed occupancy aligned to frost dates.Text alternative: Direct sow Apr 12–May 3; Tend and monitor May 3–Jun 16; Harvest Jun 16–Aug 20.

Related plants

See also: Poaceae 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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