When to plant onion in zone 3a — planting calendar

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Showing USDA Zone 3A

Growing SeasonZone 3a

Last frost ~May 30First frost ~Sep 10Today

Start indoorsTransplant / sowHarvestFrost risk

MARAPRMAYJUNJULAUGSEP

Start indoors Mar 21 · Sow May 16 · First harvest Aug 14 · Wrap by Sep 10

Last spring frostMay 30

Start seeds indoorsMar 21

Direct sowMay 16

First harvestAug 14

Last harvestSep 10

First fall frostSep 10

Why these dates work in zone 3a

Zone 3a's last spring frost averages May 30 and first fall frost Sep 10 — about 103 frost-free days. Onion tolerates light frost, so you can sow ahead of the last-frost date and keep harvesting into the cooler fall. Starting seeds indoors 10 weeks ahead gives strong transplants ready the moment the soil warms.

Common questions

How long does onion take to grow in zone 3a?

Onion matures in about 90–110 days from sowing. In zone 3a that means sowing around May 16 and first picking around Aug 14.

Will onion survive frost in zone 3a?

Yes — onion tolerates light frost. In zone 3a you can sow a little before the last frost (around May 30) and keep harvesting past the first fall frost (around Sep 10).

For soil, spacing, pests and companion planting, see the full onion growing guide →