In zone 9, sow sweet corn directly in the garden from March 10 to March 17, 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 May 29.
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 9
| Task | When |
|---|---|
| Sow outside | March 10 – March 17 |
| First harvest | May 29 – June 25 |
| Sow again | Every 7–10 days in spring |
| Side-dress with nitrogen | When plants are 15–18 inches tall |
| Watch for earworms | From silking onward |
Most of zone 9 sees its last spring frost between February 16 and March 15, with a typical date of March 3. 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 9
In zone 9, plant sweet corn early so it pollinates before the worst heat. Varieties grown in the South include:
- Yellow: Merit (su), Sugar Buns (se) and Illini Gold (sh2).
- White: Silver Queen (su), Silver King and Silver Princess (se), and Kandy Korn (se).
- Bicolor: Ambrosia, Peaches and Cream and Chubby Checkers (all se).
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 9 sweet corn tips
- Plant early. Heat or drought during tasseling leads to poor pollination and ears with few kernels.
- Check the soil temperature. Wait until the soil 4 inches down is at least 50 °F, or 65 °F for supersweet varieties.
- Expect corn earworms. They are the most common sweet corn pest in the South. Cut off damaged ear tips at harvest.
- Keep supersweet corn apart from other corn, about 400 yards, or plant it to tassel a month apart.
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
- Zone 8April 7 – April 14
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 9 in April?
For good ears, probably. Corn planted that late pollinates in peak summer heat, which leaves ears with gaps. Plant early next spring.
Why do my corn ears have missing kernels?
Usually heat or drought during tasseling, which ruins pollination. Plant early, in blocks, and water well while the silks are out.
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.