When should I plant Onion in Zone 3b?

Start Onion seeds indoors around Mar 6. Transplant outdoors after Apr 17. Expect first harvest around Jul 6.

What is the last frost date for Zone 3b?

The average last spring frost date for Zone 3b is May 15. The first fall frost averages Sep 22, giving a 130-day growing season.

Can I grow Onion in Zone 3b?

Yes. Onion needs 110 days to harvest. Zone 3b has a 130-day growing season, which is sufficient.

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🧅 Growing Onion in Zone 3b

Zone 3b has harsh winters and a short growing season. Start Onion early indoors to maximize your harvest window. Last frost: May 15. First frost: Sep 22.

Planting Calendar

Indoor

Outdoor

Harvest

Mar 6Sep 22

Season: May 15 – Sep 22 (130 days)

Zone3b

Last FrostMay 15

First FrostSep 22

Season Length130 days

Days to Harvest110

SunFull Sun

Frost ToleranceModerate

Spacing9/sqft (4" apart)

When to Plant Onion in Zone 3b

Start Seeds Indoors: Mar 6

Start Onion seeds indoors around Mar 6 (10 weeks before last frost). Optimal germination temperature: 70°F. Germinates in 7–14 days.

Transplant Outdoors: Apr 17

Transplant Onion seedlings outdoors after Apr 17. 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 6

First harvest approximately Jul 6 (~80 days from transplant). Continue harvesting until first frost (Sep 22).

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