Sweet corn planting months by climate zone
The chart comes from the same data as the planting calendar. Tap a zone for its full calendar and the towns it covers, including frost warnings by town.
| Zone | J | F | M | A | M | J | J | A | S | O | N | D | Sow or plant |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tropical | yes | yes | yes | Apr–Jun | |||||||||
| Subtropical | yes | yes | yes | yes | yes | yes | yes | yes | Aug–Mar | ||||
| Arid and semi-arid | yes | yes | yes | yes | yes | yes | Sep–Feb | ||||||
| Temperate | yes | yes | yes | yes | yes | Sep–Jan | |||||||
| Cool | yes | yes | yes | yes | Oct–Jan | ||||||||
| NZ warm north | yes | yes | yes | Oct–Dec | |||||||||
| NZ temperate | yes | yes | yes | Oct–Dec | |||||||||
| NZ cool south | yes | yes | yes | Oct–Dec |
sow or plantnot recommendedthis month
From temperate Australia south, and in New Zealand, the window opens with the warmth of spring and closes by midsummer. That leaves time for a crop that takes 11–14 weeks to ripen before autumn cools. The subtropics have a long season on either side of winter. The tropics, as the NT Government recommends, sow in the dry season from April to June.
Soil temperature
Cold soil slows corn right down. The germination table by J. F. Harrington of UC Davis, republished by Oregon State University Extension, shows how much warmth matters:
| Soil temperature | Days for seedlings to emerge |
|---|---|
| 10 °C | 22 |
| 15 °C | 12 |
| 20 °C | 7 |
| 25–30 °C | 4 |
| 35 °C | 3 |
10 °C is the minimum in that table, but it is not a target. Illinois Extension sows standard sweet corn once the soil is above about 13 °C, and supersweet varieties at about 18 °C. The University of Georgia waits for at least 16 °C. Check with a soil thermometer at seed depth in the morning. Sow about 13 mm deep in cool, moist soil and 25–38 mm deep in warm, dry soil.
Plant in blocks, not a single row
Corn is pollinated by wind. Pollen falls from the tassels at the top onto the silks below, and each silk that catches a grain becomes one kernel. Plant one long row and much of the pollen blows away, leaving cobs with gaps. So plant a square block of short rows, 20–30 cm apart. The planting calendar suggests at least three rows, and the University of Georgia four or more. Illinois Extension notes that pollination takes about 5 days after the first silks appear. Keep the water up then: Georgia puts corn's needs at about 25 mm a week, and most of all during pollination and while the cobs fill.
Standard, sugary enhanced and supersweet
- Standard (su) varieties are creamy, but their sugar turns to starch within days of picking.
- Sugary enhanced (se) varieties are sweeter and still tender. The University of Georgia says they need no isolation from other types.
- Supersweet (sh2) varieties stay sweet longer after picking, with crisper kernels. They must not cross with other corn. If they are pollinated by standard sweet corn, popcorn or field corn, the kernels come out starchy and tough.
How far apart is far enough? Illinois says at least 150 m, especially downwind, and Georgia says about 365 m. Neither is possible in a backyard. So grow one type at a time, or time the sowings so the two types don't tassel together. Georgia suggests maturity dates about a month apart.
When to pick
Illinois Extension times the harvest about 20 days after the first silks appear. The signs are:
- brown, drying silks
- full kernels right to the tip
- firm cobs
- kernels that are smooth and plump and squirt milky juice when pressed with a thumbnail
Sweet corn stays at this milk stage for less than a week, so check daily once the silks brown. Standard varieties lose sweetness quickly, so cook them the day you pick.
Questions
When should I plant sweet corn in Melbourne?
Melbourne is in the cool zone, where the calendar gives October to January. Wait until the soil is above about 13 °C, or 18 °C for supersweet varieties, and until the frosts have finished.
Why are my corn cobs only half full?
Usually poor pollination. Every kernel needs pollen to land on its own silk, which happens far more reliably in a block of short rows than in a single row. Dry soil while the silks are out makes it worse.
How do I know when sweet corn is ready?
About 20 days after the silks first appear, when the silks are brown and dry and the cob feels firm and full. Press a kernel with your thumbnail: milky juice means it is ready.
Can I grow supersweet corn next to other corn?
Not if they flower at the same time. Pollen from standard sweet corn, popcorn or field corn makes supersweet kernels starchy. Grow one type per season, or sow them far enough apart in time that they don't tassel together, about a month between maturity dates.
Sources
- Illinois Extension, Corn. Covers soil temperatures for standard and supersweet corn, sowing depth, isolation, pollination time, harvest timing and the milk stage.
- University of Georgia Extension, Growing home garden sweet corn (C 905). Covers the su, se and sh2 types, isolation distance and timing, soil temperature, planting in blocks, spacing and watering.
- Oregon State University Extension, Soil temperature conditions for vegetable seed germination, after J. F. Harrington, UC Davis.
- Planting months, spacing and days to harvest: the GardenMaths planting calendar, from ABC Gardening Australia, the NT Government, Tui and others listed on each zone page.
Last reviewed 24 September 2026 · Report an error