In zone 4, sow sweet corn directly in the garden from May 23 to May 30, one to two weeks after your last spring frost, once the soil is at least 50 °F (65 °F for supersweet types). Expect ripe ears in about 80–100 days, from around August 11.
Sweet corn dates for your ZIP code
Planting times based on university extension guidance (UNH, Cornell, Purdue, Minnesota, Nebraska and UMass Extension). Frost dates from NOAA 1991–2020 U.S. Climate Normals, nearest weather station. Zones derived from the 2023 USDA Plant Hardiness Zone Map data (PRISM Climate Group, Oregon State University). This is not the official USDA Plant Hardiness Zone Map.
Sweet corn timing in zone 4
| Task | When |
|---|---|
| Sow outside | May 23 – May 30 |
| First harvest | August 11 – September 7 |
| Sow again | Every 7–10 days, or plant early and late varieties together |
| Side-dress with nitrogen | When plants are 15–18 inches tall |
| Water | About 1 inch a week, especially before silks appear |
Most of zone 4 sees its last spring frost between May 11 and May 23, with a typical date of May 16. Corn seed rots in cold, wet soil, so the soil temperature matters more than the calendar date. The tool above uses the weather station closest to your ZIP code.
Why sweet corn waits for warm soil
Sweet corn is a warm-season crop. Frost damages it, and its seed rots in cold, wet soil. It germinates best at soil temperatures of 60–85 °F and needs at least 50 °F, or 65 °F for supersweet varieties. That is why it is sown one to two weeks after the last spring frost.
Best sweet corn varieties for zone 4
In zone 4, choose early varieties with the fewest days to maturity, and types that sprout in cool soil:
- Sugar-enhanced (se) varieties such as Sugar Buns, Peaches and Cream and Ambrosia: sweeter than standard corn, hold their sugar longer, and germinate in cooler soil.
- Standard (su) varieties such as Early Sunglow: an early option for cool areas.
- Supersweet (sh2) varieties are the sweetest but sprout poorly in cold, wet soil. Wait until the soil reaches 65 °F.
How to plant sweet corn
- Sow directly in the garden, about 1 inch deep in early plantings and 1–2 inches later in the season.
- Space seeds 8–10 inches apart in rows 2½–3 feet apart.
- Plant in a block of at least three or four short rows for good pollination.
- Fertilize before planting, then side-dress with nitrogen when plants are 15–18 inches tall.
- Water about an inch a week, especially in the two weeks before silks appear.
Zone 4 sweet corn tips
- Don’t sow into cold soil. Below 50 °F, seed rots. In early sowings, plant no deeper than 1 inch.
- Plant in blocks, not one long row. Corn is wind-pollinated, and a block of several short rows gives fuller ears.
- Keep supersweet corn apart. If it crosses with other corn, both lose quality. Separate them or plant them so they don’t tassel at the same time.
- Stagger plantings every 7–10 days for a longer harvest.
Harvesting sweet corn
Sweet corn is ready about 20 days after the first silks appear, when the silks are dry and brown, the husks are still green and the ears feel plump. Pull back a husk to check: the kernels should be full and milky. Pick in the cool of early morning and refrigerate right away, because the sugar turns to starch quickly in warm temperatures.
Sweet corn planting dates in nearby zones
See dates for every zone on the sweet corn planting guide, or build a full schedule with the planting calendar.
Frequently asked questions
Is it too late to plant sweet corn in zone 4 in June?
It may be. Corn needs 80–100 days, and your first fall frost comes around September 25. If you sow in June, choose the earliest variety you can find.
Why do my corn ears have missing kernels?
Poor pollination. Each kernel needs pollen from the tassels. Plant in blocks of several short rows, and keep the plants watered when the silks appear.
What do su, se and sh2 mean on sweet corn seed?
They are sweetness types. Standard (su) is the classic flavor, sugar-enhanced (se) is sweeter and holds its sugar longer, and supersweet (sh2) is the sweetest but needs warm soil and must be kept apart from other corn.
Why plant sweet corn in blocks?
Corn is pollinated by wind, and each kernel needs its own grain of pollen. A block of several short rows catches pollen much better than a single long row.
How long does sweet corn take to grow?
About 80–100 days from sowing, depending on the variety.
Sources. Planting dates use the median frost dates of each USDA zone, calculated from NOAA climate data for every ZIP code in the zone.