Sweet Corn in Zone 4a & 4b
Zea mays
When to plant sweet corn in zone 4b
Zones 4a and 4b share the same average frost dates in our data, so this page covers both.
Method: Direct sow: Direct-sow outside. Sweet Corn doesn't transplant well, or doesn't need the extra time indoors.
| Start indoors | Not typically started indoors |
|---|---|
| Direct sow / transplant outside | May 22–May 29 |
| Estimated harvest | Aug 5–Aug 12 (~75 days after direct-sowing) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 5-8 ft.
Corn takes up a full square foot per plant and grows tall enough to shade everything around it, so it's a bigger commitment than most vegetables, and unlike almost everything else in the garden, it needs company. A single row or a lonely handful of stalks is the most common way home gardeners end up with ears full of blank, unpollinated patches.
How sweet corn fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Sweet Corn needs about 75 days from sowing to first harvest.
Good companions
- Bush Beans: The classic 'three sisters' pairing. WSU Extension confirms the real mechanism: beans climb corn stalks and fix nitrogen the corn uses.
- Winter Squash: The third 'three sisters' pairing. WSU Extension confirms squash's broad leaves shade the soil, reducing evaporation and suppressing weeds around corn.
Where to buy sweet corn seeds
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing sweet corn" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 4b calendar · Full companion planting guide · Full plant profile · Plan your beds in the Garden Designer →
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Growing Sweet Corn in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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