How to Grow Sweet Corn: Planting, Spacing, Care & Harvest

Quick answer

Sow sweet corn after frost danger is past and soil has warmed — about 60 degrees F for many types, about 65 degrees F for supersweet (UMD; UMN). Plant in a block of at least three to four rows for pollination. Pick when kernels are milky and silks are browning, about 17 to 24 days after first silk.

Sweet corn at a glance

PlantDirect sow: 1–2 wk after last frost
SunFull sun (UMD).
WaterUMN about 1 inch per week; UMD uniform moisture especially at establishment, flowering, and ear fill.
SpacingUMN: plant 1 inch deep (shrunken types no deeper than ¾–1 inch); 8 to 12 inches apart in the row; rows 30 to 36 inches.
Days to harvest80-95
-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.
Jump to

Updated

Planting dates for your ZIP: the ZIP planting planner counts each window from your local frost dates.

Organic pests and diseases: see also organic pest control. Use any product as the label directs.

Boiled sweet corn on the cob
Sweet corn on the cob. Photo: Undeka 11, Wikimedia Commons, CC BY-SA 4.0.

Planting timing

UMD: very tender warm-season annual; “Seed after the danger of frost is past; super-sweet varieties should be planted when soil temperatures reach 65°F.” (UMD Extension) UMN: direct seed after soil has warmed; seeds germinate best near 60°F soil; shrunken (sh) supersweet types often need warmer soil near 65°F (UMN Extension). Prefer frost-passed plus soil-warm language; link the ZIP planner.

Isolation and block planting

Wind-pollinated. Plant in blocks of at least four rows (UMN) / minimum three rows, preferably four (UMD) — not a single long row — or ears will have blank kernels. Isolate genetic types and field corn by distance or time. UMN: about 300 feet from field corn; home gardens often isolate by planting types at least two weeks apart in maturity/pollen time, or grow only one type. UMD: extra-sweet vs standard isolation by 400 yards or two weeks. Sources differ on distance — present both; stress time isolation as the practical home-garden option. Genetic types (su/se/sh/sy) may be explained without naming cultivars.

Depth and spacing

UMN: plant 1 inch deep (shrunken types no deeper than ¾–1 inch); 8 to 12 inches apart in the row; rows 30 to 36 inches. UMD: 9–12 inches in-row × 24–36 inches between rows. Succession (UMD): every two weeks or when prior planting has 3–4 leaves.

Sun, soil and water

Full sun (UMD). UMN: well-drained soil with organic matter; pH 5.8 to 7.0; no fresh manure; no fertilizer with weed killer. Water: UMN about 1 inch per week; UMD uniform moisture especially at establishment, flowering, and ear fill. Side-dress when plants are about 1 foot tall (UMN) / 12–18 inches and again at tassel (UMD) using soil-test–based organic sources only — no synthetic product rates.

Care

Do not remove suckers — may reduce yield (UMD). Optional string support around the block to reduce lodging (UMD). Shallow cultivation for weeds until canopy shades the row (UMN).

Harvest and storage

Days to maturity: UMD 63–100; Clemson planning citation 80–95 — show both. Ready when kernels in mid-ear are full and milky if squeezed; silks drying/brown (UMN; UMD). Timing about 18–24 days after first silk (UMN) / 17–24 days (UMD). Fridge life depends on genetic type: traditional sugary types lose quality fast (same-day best per UMN); newer types hold longer (UMN up to a week+; UMD newer types 2–3 weeks) — label by source/type.

Pests and diseases (organic)

Corn earworm: caterpillar in ear tip; cut off damaged tip and eat the rest if found in the kitchen (UMN). UC IPM: early plantings less damaged than late; optional few drops of mineral oil on silks 3–5 days after silks appear; spinosad or Bacillus thuringiensis on silks on a short interval schedule — follow the label; destroy culls after harvest (UC IPM).

Birds and raccoons: row cover until emergence against seed-eating birds; fencing where needed (UMN).

Smut: cut out galls before they spore; remove from garden; do not compost (UMN). Leaf rust: resistant cultivars as a practice note only — no named list (UMN).

Related: organic pest control · ZIP planner · popcorn

Frequently asked questions

Why plant corn in a block?

Wind pollination — single rows leave blank kernels (UMN; UMD).

When is an ear ready?

Milky kernels, browning silks, about 17–24 days after first silk (UMD; UMN).

How do I limit earworms organically?

Prefer early plantings; mineral oil on young silks; Bt or spinosad on silks per label before larvae enter the ear; cut damaged tips (UC IPM; UMN).

More grow guides: Carrots · Strawberries · Shallots · Raspberries · Spinach · Beets · Dill · Bok Choy · Brussels Sprouts · Collards · All grow guides

Sources