When should I plant Onion in Zone 5b?

Start Onion seeds indoors around Feb 17. Transplant outdoors after Mar 31. Expect first harvest around Jun 19.

What is the last frost date for Zone 5b?

The average last spring frost date for Zone 5b is Apr 28. The first fall frost averages Oct 8, giving a 163-day growing season.

Can I grow Onion in Zone 5b?

Yes. Onion needs 110 days to harvest. Zone 5b has a 163-day growing season, which is sufficient.

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🧅 Growing Onion in Zone 5b

Zone 5b has cold winters and a moderate growing season. Timing is key for Onion in this zone. Last frost: Apr 28. First frost: Oct 8.

Planting Calendar

Indoor

Outdoor

Harvest

Feb 17Oct 8

Season: Apr 28 – Oct 8 (163 days)

Zone5b

Last FrostApr 28

First FrostOct 8

Season Length163 days

Days to Harvest110

SunFull Sun

Frost ToleranceModerate

Spacing9/sqft (4" apart)

When to Plant Onion in Zone 5b

Start Seeds Indoors: Feb 17

Start Onion seeds indoors around Feb 17 (10 weeks before last frost). Optimal germination temperature: 70°F. Germinates in 7–14 days.

Transplant Outdoors: Mar 31

Transplant Onion seedlings outdoors after Mar 31. Wait until soil temperature reaches 45°F. Space plants at 9/sqft (4" apart). Harden off plants for a week before moving outside.

Harvest: Jun 19

First harvest approximately Jun 19 (~80 days from transplant). Continue harvesting until first frost (Oct 8).

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