Sweet corn is one of the great rewards of the summer garden. There’s almost nothing better than ears picked and cooked within minutes — the sugar starts converting to starch immediately after harvest, so homegrown corn from a well-timed planting is a genuinely different experience from anything you can buy.
But corn has strict timing requirements. Plant it too early and seeds rot in cold soil. Plant too late and the ears won’t ripen before fall frost. This guide gives you exact planting dates by zone.
When to Plant Corn by Zone
Corn needs soil temperatures of at least 60°F to germinate reliably — 65–70°F is ideal. Plant after your last frost date, once the soil has warmed. Corn planted in cold soil germinates unevenly, sits for weeks, and is often outcompeted by weeds before it gets established.
| USDA Zone | First Planting | Last Planting |
|---|---|---|
| Zone 3 | Jun 1 – Jun 8 | Jun 15 |
| Zone 4 | May 22 – May 29 | Jun 15 |
| Zone 5 | May 7 – May 14 | Jun 30 |
| Zone 6 | Apr 22 – Apr 29 | Jul 1 |
| Zone 7 | Apr 12 – Apr 19 | Jul 1 |
| Zone 8 | Mar 27 – Apr 3 | Jul 15 |
| Zone 9 | Mar 7 – Mar 14 | Jul 15 |
| Zone 10 | Feb 7 – Feb 21 | Jul 31 |
Last planting dates ensure ears ripen at least 2 weeks before your first fall frost. Subtract your variety’s days-to-maturity from the first frost date to find your last safe planting date.
Why Corn Needs Warm Soil
Unlike cool-season crops that can germinate in near-freezing soil, corn seeds require warmth to germinate. In soil below 55°F, germination is slow and uneven, and seeds can rot before sprouting. Below 50°F, germination fails almost entirely. Wait for the soil to warm — the extra patience pays off with much better stands.
A soil thermometer is the most reliable tool for timing corn planting. Check soil temperature at 2–3 inch depth in the morning (that’s when it’s coolest) for 3–5 days in a row. Once you’re consistently above 60°F, you’re ready to plant.
Succession Planting for Extended Harvest
Sweet corn matures all at once — a whole planting ripens within a few days of each other. To extend your harvest, make 2–3 successive plantings spaced 2–3 weeks apart (within the window shown in the table above).
Alternatively, plant early, mid-season, and late-maturing varieties at the same time. The different maturity dates stagger your harvest without multiple planting dates.
Important: Don’t plant different corn varieties that mature at the same time within 400 feet of each other — they’ll cross-pollinate, which doesn’t affect the harvest year but can cause quality problems if you save seeds, and may affect flavor in some sweet corn types.
Plant in Blocks, Not Single Rows
Corn is wind-pollinated. Pollen from the tassels (top of the plant) must fall onto the silk (the silky strands emerging from the ear). In a single long row, pollen drifts away from the ears and pollination is poor — resulting in ears with missing kernels.
Always plant corn in blocks of at least 4 rows wide. In a small garden, a 4×4 grid of 16 plants pollinates well. The block can be any shape as long as you have multiple rows in all directions.
Planting Depth and Spacing
Plant seeds 1 inch deep in cool soil, up to 2 inches deep in warm soil (deeper planting helps with moisture and anchorage). Space seeds 9–12 inches apart in rows 24–30 inches apart. If you plant closer together in a small garden, thin to the best seedling per spot once plants are 4 inches tall.
Choosing the Right Variety
For short-season zones (3–4), choose varieties that mature in 65–75 days: ‘Early Sunglow’ (62 days), ‘Quickie’ (65 days), ‘Bodacious RM’ (75 days). For zones 5–8, standard varieties that mature in 75–85 days give the best flavor: ‘Incredible’ (85 days), ‘Ambrosia’ (75 days), ‘Silver Queen’ (92 days — only for longer seasons).
