Sweet Corn in Zone 4a & 4b
Zea mays
Yes, sweet corn grows in zones 4a and 4b. Plant it outside May 22–May 29.
When to plant sweet corn in zone 4b
Zones 4a and 4b share the same average frost dates, so this page covers both.
Method: Direct sow: Direct-sow outside. It 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.
Plant alongside it in zone 4b
These go outside within two weeks of sweet corn in zone 4b, so one planting day can cover them.
- TomatoMay 29–Jun 5
- CucumberMay 22–May 29
- ZucchiniMay 22–May 29
- BroccoliniMay 15–May 22
- Napa Cabbage (Chinese Cabbage)May 15–May 22
- BurdockMay 22–May 29
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.
Sweet Corn planting windows in every zone
Zone 4b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Harvest |
|---|---|---|---|
| 3a & 3b | Not usually | Jun 6–Jun 13 | Aug 20–Aug 27 |
| 4a & 4b (your zone) | Not usually | May 22–May 29 | Aug 5–Aug 12 |
| 5a & 5b | Not usually | May 17–May 24 | Jul 31–Aug 7 |
| 6a & 6b | Not usually | May 2–May 9 | Jul 16–Jul 23 |
| 7a & 7b | Not usually | Apr 17–Apr 24 | Jul 1–Jul 8 |
| 8a & 8b | Not usually | Apr 1–Apr 8 | Jun 15–Jun 22 |
| 9a & 9b | Not usually | Feb 22–Mar 1 | May 8–May 15 |
| 10a & 10bSpring window | Not usually | Feb–Mar | ~75 days after direct-sowing |
| Summer window | Not usually | Jul–Aug | ~75 days after direct-sowing |
Harvest dates are about 75 days after the sow or plant-out date.
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
True Leaf Market · High Mowing Organic Seeds (each supplier's sweet corn seeds)
Varieties we recommend, and where to get them:
- Ambrosia (se): One of UMN Extension's named sugary-enhanced examples, raising sugar levels 30-35% over standard sugary corn and slowing sugar-to-starch conversion after harvest for better fresh-eating quality. Buy: Botanical Interests · Burpee Full notes
- Northern Xtra Sweet (supersweet/sh2): UMN's example of the shrunken (sh2) supersweet type, 40-50% sugar against se's 30-35%, crisper but less traditionally creamy in texture per UMN's own comparison. Buy: Burpee Full notes
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 · 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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