When should I plant Onion in Zone 3a?

Start Onion seeds indoors around Mar 13. Transplant outdoors after Apr 24. Expect first harvest around Jul 13.

What is the last frost date for Zone 3a?

The average last spring frost date for Zone 3a is May 22. The first fall frost averages Sep 12, giving a 113-day growing season.

Can I grow Onion in Zone 3a?

Yes. Onion needs 110 days to harvest. Zone 3a has a 113-day growing season, which is sufficient.

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🧅 Growing Onion in Zone 3a

Zone 3a has harsh winters and a short growing season. Start Onion early indoors to maximize your harvest window. Last frost: May 22. First frost: Sep 12.

Planting Calendar

Indoor

Outdoor

Harvest

Mar 13Sep 12

Season: May 22 – Sep 12 (113 days)

Zone3a

Last FrostMay 22

First FrostSep 12

Season Length113 days

Days to Harvest110

SunFull Sun

Frost ToleranceModerate

Spacing9/sqft (4" apart)

When to Plant Onion in Zone 3a

Start Seeds Indoors: Mar 13

Start Onion seeds indoors around Mar 13 (10 weeks before last frost). Optimal germination temperature: 70°F. Germinates in 7–14 days.

Transplant Outdoors: Apr 24

Transplant Onion seedlings outdoors after Apr 24. Wait until soil temperature reaches 45°F. Space plants at 9/sqft (4" apart). Harden off plants for a week before moving outside.

Harvest: Jul 13

First harvest approximately Jul 13 (~80 days from transplant). Continue harvesting until first frost (Sep 12).

Companion Planting

✅ Strawberries✅ Cabbage✅ Beets✅ Lettuce✅ Carrots✅ Tomatoes

❌ Beans❌ Peas

Onion in Other Zones

1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b 10a 10b 11a 11b 12a 12b 13a 13b

Plan Your Onion Garden

Track Onion from seed to harvest with personalized frost dates, watering recommendations, and companion planting visualization.

Start Free Onion Growing Guide