key growing information

Growing Sweet Corn: How to Plant, Grow & Harvest

How to grow sweet corn: soil temperature for treated and untreated seed, isolating super sweets, spacing and blocks for pollination, harvest timing and seeding rates.

By Hensley’s Seed Co. September 3, 2026

Sweet Corn - Key Growing Information

An ear of developing sweet corn; a stalk at right shows male flowers with anthers and pollen.

SCIENTIFIC NAME:

Zea mays

CULTURE:

Cold soil means poor germination. Wait for soil of at least 65°F (18°C) for untreated seed and 60°F (16°C) for treated seed. Only treated seed of varieties known for good cold germination should go into 55°F (13°C) soil, and only when warmer weather is on the way. Floating row covers over early plantings help even out soil temperatures.

DAYS TO MATURITY:

Counted from direct sowing. Weather and planting date shift maturity a great deal, so use these numbers to compare varieties rather than to predict an exact harvest day.

ISOLATION REQUIREMENTS:

Super sweet types crossed heavily with other sweet corn give tough, starchy kernels in both. If you grow both kinds, prevent cross-pollination in one of three ways: 1) keep super sweets at least 300' from other types; 2) plant 12 days apart and keep the plantings 25' apart; or 3) choose varieties whose maturity dates differ by at least 12 days and keep them 25' apart. DIRECT SEEDING: Plant ¾–1" deep, 6–7" apart (or 2 seeds every 9", later thinned to one), in rows 30–36" apart; sow a little more heavily if the seed is untreated. Corn is wind-pollinated, so plant in blocks of at least 4 rows to get well-filled ears. You can keep planting into early summer, and many growers stretch the season by growing several varieties with different maturity dates.

AVG. DIRECT SEEDING RATE:

At 2 seeds per foot in rows 36" apart: 1,000 seeds sow about 500', 5,000 about 2,500', 25,000 about 12,500'; plan on roughly 30,000 seeds per acre.

INSECT PESTS:

Your local Cooperative Extension office can advise on integrated pest management. Plowing under or pulling and composting stalks promptly after harvest reduces insect pressure on next year's corn.

HARVEST:

Pick when kernels are plump and sweet; the silks drying and turning brown is the usual sign. Note the day when about half the plants are silking: ears are generally ready 18–24 days later, sooner in hot weather.SEEDS/LB.: About 2,700 per lb. for su, se and synergistic types; about 2,900 per lb. for super sweet types.

PACKET:

150 seeds per packet, enough for about 75' at 2 seeds per foot.