When should I plant Onion in Zone 4a?

Start Onion seeds indoors around Feb 24. Transplant outdoors after Apr 7. Expect first harvest around Jun 26.

What is the last frost date for Zone 4a?

The average last spring frost date for Zone 4a is May 5. The first fall frost averages Oct 1, giving a 149-day growing season.

Can I grow Onion in Zone 4a?

Yes. Onion needs 110 days to harvest. Zone 4a has a 149-day growing season, which is sufficient.

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🧅 Growing Onion in Zone 4a

Zone 4a has cold winters and a moderate growing season. Timing is key for Onion in this zone. Last frost: May 5. First frost: Oct 1.

Planting Calendar

Indoor

Outdoor

Harvest

Feb 24Oct 1

Season: May 5 – Oct 1 (149 days)

Zone4a

Last FrostMay 5

First FrostOct 1

Season Length149 days

Days to Harvest110

SunFull Sun

Frost ToleranceModerate

Spacing9/sqft (4" apart)

When to Plant Onion in Zone 4a

Start Seeds Indoors: Feb 24

Start Onion seeds indoors around Feb 24 (10 weeks before last frost). Optimal germination temperature: 70°F. Germinates in 7–14 days.

Transplant Outdoors: Apr 7

Transplant Onion seedlings outdoors after Apr 7. 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 26

First harvest approximately Jun 26 (~80 days from transplant). Continue harvesting until first frost (Oct 1).

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