Sweet Corn in Zone 3a & 3b
Zea mays
When to plant sweet corn in zone 3b
Zones 3a and 3b 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 | Jun 6–Jun 13 |
| Estimated harvest | Aug 20–Aug 27 (~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 3's season
Zone 3b's frost-free window runs about 98 days, from May 30 to September 5. 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 3b 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 3b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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