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Sweet Corn

Zea mays var. saccharata (also var. rugosa)

VegetableSummer Medium

Tall, fast, and unmistakably summer. Corn is wind-pollinated, so plant it in a block — never a single row — and keep super-sweet types isolated from other corn to stay tender.

Growing conditions

Light
Full sun — at least 6–8 hours of direct sun per day
Water
Medium
Soil
Deep, fertile, well-drained loam rich in organic matter; needs steady nitrogen · pH 6.0–6.8 (slightly acidic to neutral)
When to sow
Sow 1–2 weeks AFTER the last spring frost, once both frost danger has passed and the soil has warmed. Corn is frost-tender — a light frost kills seedlings.
Spacing
Plant in a BLOCK of at least 4 short rows (not one long row). Space seeds 20–25 cm (8–10 in) apart within the row, with rows 60–90 cm (24–36 in) apart. Thin seedlings to ~25–30 cm (10–12 in) apart.
Days to maturity
60–100 days from direct sowing — early types 60–70, midseason 70–80, late 80+ (supersweet/sh2 often run longer)
Hardiness
Grown as a summer annual in USDA zones 3–11; not winter-hardy anywhere — it is the length of the warm, frost-free season (roughly 60–100 days) that limits which varieties you can ripen, not the zone's winter low.

How to grow it

  1. 1

    Sow in a block, in warm soil

    Wait until the frost is past and the soil is reliably 16°C (60°F)+ — supersweet seed wants 18°C (65°F) or it rots. Sow 2.5–4 cm (1–1.5 in) deep, then arrange the rows as a square block of at least four short rows rather than one long line. Corn is wind-, so this block layout is what lets the tassels (the male flowers on top) shower pollen onto the silks (each silk feeds one kernel) of neighboring plants.

  2. 2

    Thin and keep weeds down early

    Once seedlings are up, thin to one strong plant every 25–30 cm (10–12 in) so they aren't crowded — crowded corn pollinates poorly and makes gappy ears. Cultivate shallowly to kill weeds while plants are small; corn roots are near the surface, so hoe lightly.

  3. 3

    Feed heavily — corn is hungry

    Work and a complete into the bed before sowing. Then side-dress (feed) with nitrogen twice: about 14 g/m² (½ lb of 21-0-0 per 100 sq ft) when plants are knee-high (8–10 leaves), and again as the first tassels and silks appear. Place fertilizer ~15 cm (6 in) to the side of the row and water it in.

  4. 4

    Water deeply, especially at tasseling

    Give corn about 2.5 cm (1 in) of water per week, and never let it stress for moisture from tasseling through ear fill — this is when kernels set. Deep water at the base rather than overhead, and between rows to hold moisture and suppress weeds.

  5. 5

    Help pollination and consider hilling

    Corn relies on wind to , not bees — the block planting does the work, but on a small patch you can hand-pollinate by snapping off a tassel and dusting the silks on a calm morning. As plants grow tall, mounding ( up / hilling) soil 10–15 cm (4–6 in) around the base and letting the prop roots anchor helps them resist lodging in wind.

  6. 6

    Succession-sow for a long harvest

    Because each block ripens within a few days, plant a new block every 10–14 days, or plant early, mid, and late varieties together, so you aren't flooded with corn all at once. You can also try the Three Sisters method — corn as the pole for climbing beans, with squash sprawling below as living .

Gardener's notes

  • Isolate sugar types: a single supersweet (sh2) block tasseling near your su or se corn will cross- it into tough, starchy kernels — separate incompatible types by ~75 m (250 ft) or stagger planting by 2–3 weeks. This 'xenia' effect changes the kernels on the current ear, not just next year's seed.
  • Pick at milk stage, not by the calendar: the perfect window is only a few days. Watch the silks browning and use the thumbnail/milky-juice test rather than trusting the days-to-maturity number, which shifts with weather.
  • It's wind, not bees: corn is wind-, so a tight block of several short rows out-yields a long single row every time — and on a tiny patch you can hand-shake the tassels over the silks on a calm morning to fill the ears.

Varieties worth knowing

Standard sugary (su) — e.g. 'Silver Queen', 'Golden Bantam'
su type: classic 'old-fashioned' corn flavor, tender but converts sugar to starch fast after picking, so eat or process within hours. Compatible with se; will be ruined (starchy) if it cross-pollinates with sh2 — keep isolated from supersweets.
Sugary enhanced (se / se+) — e.g. 'Bodacious', 'Ambrosia', 'Kandy Korn'
se type: extra-tender, sweeter than su, and holds sweetness a few days longer after harvest. Generally compatible with su and synergistic types in the same patch; the best all-round home-garden choice. Keep away from sh2.
Supersweet (sh2) — e.g. 'Honey Select' (note: a synergistic), 'Xtra-Tender', 'Mirai' series
sh2 type: the sweetest and crunchiest, with the longest shelf life — but the seed germinates poorly in cool soil and MUST be isolated from all other corn (su, se, synergistic, field corn, popcorn). Isolate by ~75 m (250 ft) OR by 2–3 weeks of staggered planting (tasseling time), or cross-pollination yields tough, starchy kernels.
Synergistic (sy: su/se/sh2 blend) — e.g. 'Serendipity', 'Synergy'
Each ear carries a mix of se and sh2 kernels for sweetness plus creamy texture. Plant with se and su; isolate from straight sh2 supersweets to avoid quality loss from xenia (pollen directly affecting kernel quality on the same ear).

Common problems & fixes

Corn earworm
Sign: Caterpillars chewing down from the silk end of the ear, leaving frass and damaged tip kernels.
Fix: Choose tight-husked varieties, which resist entry. Apply a few drops of mineral oil (or Bt) to the silk tip about 5–6 days after silks emerge, repeating as needed. Once the worm is inside the ear it can't be controlled, so timing is everything — just trim the damaged tip at harvest.
Raccoons (and birds/deer)
Sign: Whole stalks knocked over and ears stripped or half-eaten overnight, almost always the night before you planned to pick.
Fix: A two-strand electric fence (wires at ~15 cm/6 in and 30 cm/12 in) is the most reliable deterrent. Harvesting promptly at peak and not leaving over-ripe ears in the patch also reduces the lure.
Poor pollination / gappy ears
Sign: Ears with scattered missing kernels or bare patches, often at the tip.
Fix: Plant in a block of 4+ rows, not a single line; thin to proper spacing; water through tasseling/silking; and isolate incompatible sugar types. Drought, crowding, and single-row planting are the usual culprits — not a seed problem.
Common smut (Ustilago maydis)
Sign: Swollen, silvery-grey galls on ears, tassels, or stalks that rupture into a mass of black spores.
Fix: Cut off and bag galls before they burst, rotate crops, avoid wounding plants and over-applying nitrogen, and keep pollination strong (poor pollination worsens it). Use resistant hybrids. (Note: in Mexico the young galls, 'huitlacoche', are a prized edible.)

Companions

Grows well with
Pole beans (Three Sisters — fix nitrogen and climb the stalks)Winter squash / pumpkins (Three Sisters — shade soil, suppress weeds)CucumbersMelonsPeas
Keep apart from
Tomatoes (share the corn earworm / tomato fruitworm pest)Incompatible corn sugar types nearby (sh2 supersweet beside su/se ruins kernel quality via cross-pollination)

Harvest & storage

Harvest
Harvest at the 'milk stage', about 18–24 days after the silks first appear. The signs: silks are brown and dry but the husk is still green and tight, the ear feels firm and full to the tip. Confirm with the thumbnail test — peel back a little husk and press a kernel; a thin, milky juice means it's ready (clear/watery = too early, thick/doughy = past prime). Pick by holding the stalk and twisting the ear down and off.
Storage
Sweet corn is best eaten the day it's picked — su types lose sweetness within hours as sugar turns to starch (se and especially sh2 types hold longer). Pick in the cool of early morning and chill immediately. Refrigerate in the husk as close to 0°C (32°F) as possible; quality holds only about 5 days. To keep it, blanch and freeze, or cut and freeze the kernels.

Sources

This guide is curated from authoritative horticulture references — primarily US university Extension services, the USDA, and the RHS.