When to plant onion in zone 5a — planting calendar

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Showing USDA Zone 5A

Growing SeasonZone 5a

Last frost ~May 10First frost ~Oct 1Today

Start indoorsTransplant / sowHarvestFrost risk

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Start indoors Mar 1 · Sow Apr 26 · First harvest Jul 25 · Wrap by Aug 22

Last spring frostMay 10

Start seeds indoorsMar 1

Direct sowApr 26

First harvestJul 25

Last harvestAug 22

First fall frostOct 1

Why these dates work in zone 5a

Zone 5a's last spring frost averages May 10 and first fall frost Oct 1 — about 144 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 5a?

Onion matures in about 90–110 days from sowing. In zone 5a that means sowing around Apr 26 and first picking around Jul 25.

Will onion survive frost in zone 5a?

Yes — onion tolerates light frost. In zone 5a you can sow a little before the last frost (around May 10) and keep harvesting past the first fall frost (around Oct 1).

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