Sweet Corn planting dates by zone

Su, se, sh2: the code on the packet

University of Minnesota Extension says three genes control sweetness, and seed packets mark them. Standard sugary (su) corn has the classic flavor and creamy kernels but turns to starch quickly, so pick it the day you eat it. Sugary enhanced (se) corn is sweeter and more tender and holds its sweetness for days in the refrigerator. Shrunken or supersweet (sh2) corn is sweeter still and crisp, and keeps for about a week. Synergistic (sy) types combine the genes. Minnesota says these are classic plant breeding, not genetic engineering.

University of Illinois Extension calls se types the gourmet choice for home gardens and says, unless the corn must be stored or shipped, they eat better than supersweets. Clemson Cooperative Extension’s Home & Garden Information Center says su and se corn germinate in cooler soil and need no isolation from each other.

For short seasons choose early varieties. Utah State University Extension says sweet corn takes 60 to 90 days from planting; early varieties suit short, cool seasons and make smaller, less sweet ears, while late varieties suit long, warm ones. Minnesota’s list runs from ‘Northern Xtra Sweet’ at 63 days and ‘Quickie’ at 67 to ‘How Sweet It Is’ at 87 and ‘Silver Queen’ at 92.

When to sow

Corn needs warm soil. Minnesota sows direct once the soil has warmed and checks it with a soil thermometer. Illinois makes early plantings of standard varieties at, or just before, the frost-free date; Utah State plants after the last frost-free date. Supersweet seed is the fussiest: Minnesota, Illinois and Clemson all say it germinates poorly in cold, wet soil, so plant it later.

The table dates the first sowing 1 week after each zone’s median last spring freeze, the offset our seed-starting tool uses, and gives the cautious date the last freeze falls before in nine years of ten. Illinois and Utah State plant earlier under clear plastic, which warms the soil; Utah State sows 3 to 4 weeks early under clear plastic tunnels, and Illinois warns that unseasonable heat under clear plastic can kill seedlings.

For a long harvest, Illinois plants an early, a second-early and a main-crop variety together, then sows again each time the last planting shows three or four leaves; Clemson sows every 10 to 14 days. Illinois plants as late as the first week of July and Utah State until early July.

Spacing and pollination

Plant in blocks, not one long row. Minnesota says wind carries pollen from the tassels to the silks, and a single row loses most of it, leaving ears with blank spots; it plants at least four rows. Minnesota spaces seed eight to 12 inches apart, one inch deep, in rows 30 to 36 inches apart; Clemson 10 inches in rows 3 feet apart; Utah State 7 to 9 inches in rows 24 to 30 inches apart. UF/IFAS says small plantings can be hand-pollinated by shaking a cut tassel over the silks.

Keep types apart. Minnesota says crossing between shrunken types and any other corn gives starchy, tough kernels, and suggests 300 feet from the nearest cornfield, or varieties whose pollen comes at least two weeks apart. Illinois gives 500 feet or more for supersweets, especially downwind, and Clemson 400 yards or maturity dates a month apart.

Do not pull the side shoots. Clemson says not to remove them, and Illinois and Utah State say removing them does not raise yields; Utah State says closer spacing makes fewer.

Water and feeding

Minnesota calls an inch of rain a week good, and Clemson says at least an inch is needed for normal growth. The critical times, Clemson and Illinois say, are tasseling, silking and ear filling: Illinois says hot, dry weather at pollination leaves missing kernels, small ears and poorly filled tips.

Illinois side-dresses nitrogen when the plants are 12 to 18 inches tall; Minnesota at one foot; Utah State at 8 to 10 leaves and again when the first tassels or silks appear. Clemson says too much nitrogen makes plants fall over.

The last planting

The table’s last planting counts back 75 days from each zone’s median first fall freeze: our crop table’s 75 days from sowing to harvest, with no frost to spare, because corn is a warm-season crop. Pick an early variety for a late sowing; a 92-day ‘Silver Queen’ needs that much more time.

Southern timing

Clemson’s planting table gives the South Carolina Piedmont March 30 to May 31 and the Coastal Plain March 1 to April 15, and names ‘Early Sunglow’, ‘Illini Gold’, ‘Merit’, ‘Sugar Buns’, ‘Kandy Korn’, ‘Silver King’, ‘Silver Princess’, ‘Silver Queen’, ‘Ambrosia’, ‘Chubby Checkers’ and ‘Peaches and Cream’. UF/IFAS names ‘Silver Queen’, ‘How Sweet It Is’, ‘Sweet Ice’, ‘Sweet Riser’ and ‘Early Sunglow’ as varieties that perform well in Florida.

Texas A&M AgriLife’s home vegetable gardening guide sows sweet corn 1 to 6 weeks after the frost-free date in spring and 12 to 14 weeks before the first freeze in fall, 9 to 12 inches apart in rows 24 to 36 inches apart, with 70 to 90 days to harvest.

Harvest

Harvest at the milk stage. Illinois says it comes about 20 days after the first silks appear and lasts less than a week: the kernels are full and plump and squirt milky juice when punctured with a thumbnail, the silks are drying and brown, and the ear is full and blunt at the tip. Minnesota gives 18 to 24 days after silking and Utah State 17 to 24.

Clemson picks in the cool of early morning and chills the ears at once, because sweet corn loses sugar fast in heat. Illinois snaps the ear off with a firm downward push, twist and pull, and says to leave the husks on until cooking.

Pollination, pests and raccoons

Corn earworm is the pest you will meet most. Clemson says it is found all over South Carolina, and Illinois that it is a problem every year: the caterpillar follows the silks into the ear tip, and once inside the husk nothing reaches it. Minnesota says to cut off the damaged tip and cook the rest, and that sowing around early May with a variety under 80 days avoids much of the earworm and European corn borer damage in Minnesota. Illinois says a rubber band or clothespin on the husk tip after silking helps.

Flea beetles attack emerging plants and can carry Stewart’s wilt, Illinois says; plant resistant varieties. For smut, the swollen galls on ears and tassels, Minnesota and Illinois cut the galls out while they are firm and keep them out of the compost. Minnesota says rust-resistant varieties are the best control for leaf rust.

Raccoons take the ears just before they ripen. Minnesota, Illinois and Utah State all use a two-wire electric fence, its lowest wire a few inches above the ground, running well before the corn ripens. Minnesota keeps crows off the seed with a floating row cover until the plants emerge.

Common mistakes

• Planting into cold, wet soil. Minnesota, Illinois and Clemson say supersweet seed germinates poorly there.
• One long row. Minnesota plants blocks of at least four rows so the wind pollinates the ears.
• Planting supersweets beside other corn. Minnesota says crossing makes them starchy and tough.
• Water stress at tasseling and silking. Illinois says it leaves gaps and unfilled tips.
• Picking late. Illinois says the milk stage lasts less than a week.
• Pulling the side shoots. Clemson says not to, and Illinois says it does not raise yields.

We found no sweet corn source for Louisiana, Alabama or Mississippi that we read for this page, and UF/IFAS gives no Florida planting months. The Southern timing here is Clemson’s and Texas A&M AgriLife’s.

Questions

When should I plant sweet corn?

After the soil has warmed. Illinois plants standard varieties at or just before the frost-free date, and Utah State after it. The table on this page dates the first sowing 1 week after each zone’s median last spring freeze, from NOAA records.

What do su, se and sh2 mean on sweet corn seed?

They are sweetness genes, University of Minnesota Extension says: standard sugary (su), sugary enhanced (se) and shrunken or supersweet (sh2). Sweeter types hold their sugar longer after picking, and supersweets must be kept away from other corn.

Why are my corn ears missing kernels?

Illinois and Utah State blame dry weather at silking and pollination, crowding, low fertility and poor pollination. Plant in blocks of several rows, Minnesota says, not one long row.

How do I know when sweet corn is ready to pick?

About 20 days after the first silks, Illinois says: the silks are dry and brown, the ear is full at the tip, and a punctured kernel squirts milky juice.

How late can I plant sweet corn?

The table’s last planting is 75 days before each zone’s median first fall freeze. Illinois and Utah State sow until about the first week of July in their states.

Sources

Freeze dates on this page are NOAA 1991–2020 Climate Normals, for every station the ZIP codes in each zone cite. Zones are the USDA Plant Hardiness Zone Map, 2023. The planting rules are named beside the table. Growing advice is quoted from the extension publications below, each written for its own area.

• University of Minnesota Extension, Growing sweet corn in home gardens , by Jill MacKenzie (Reviewed 2026). Written for: Minnesota (USDA zones 3a–5a).
• University of Illinois Extension, Corn (Home Vegetable Gardening) . Written for: Illinois (USDA zones 5a–7a).
• Utah State University Extension, How to Grow Sweet Corn in Your Garden , by Daniel Drost (Published May 2020). Written for: Utah (USDA zones 4a, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b).
• Clemson Cooperative Extension, Home & Garden Information Center, Sweet Corn (HGIC 1308) (Updated January 23, 2023). Written for: South Carolina (USDA zones 8a–9b).
• UF/IFAS Gardening Solutions, Corn (Accessed October 2026). Written for: Florida (USDA zones 8b–11b).
• Texas A&M AgriLife Extension, Texas Home Vegetable Gardening Guide (EHT-077) , by Joseph Masabni (June 2014). Written for: Texas (USDA zones 6b–10b).

How we write our guides

Published October 29, 2026