🧅
🧅 Growing Onion in Zone 4b
Zone 4b has cold winters and a moderate growing season. Timing is key for Onion in this zone. Last frost: May 1. First frost: Oct 5.
Planting Calendar
Season: May 1 – Oct 5 (157 days)
When to Plant Onion in Zone 4b
Start Seeds Indoors: Feb 20
Start Onion seeds indoors around Feb 20 (10 weeks before last frost). Optimal germination temperature: 70°F. Germinates in 7–14 days.
Transplant Outdoors: Apr 3
Transplant Onion seedlings outdoors after Apr 3. 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 22
First harvest approximately Jun 22 (~80 days from transplant). Continue harvesting until first frost (Oct 5).
Companion Planting
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 13bFrequently Asked Questions
When should I plant Onion in Zone 4b?
Start Onion seeds indoors around Feb 20. Transplant outdoors after Apr 3. Expect first harvest around Jun 22.
What is the last frost date for Zone 4b?
The average last spring frost date for Zone 4b is May 1. The first fall frost averages Oct 5, giving a 157-day growing season.
Can I grow Onion in Zone 4b?
Yes. Onion needs 110 days to harvest. Zone 4b has a 157-day growing season, which is sufficient.
What is the best month to plant Onion in Zone 4b?
The best time to start Onion in Zone 4b is Feb. Begin seeds indoors around Feb 20, then transplant outdoors after the last frost date of May 1.
What companion plants grow well with Onion?
Good companion plants for Onion include Strawberries, Cabbage, Beets, Lettuce, Carrots, Tomatoes. Avoid planting Onion near Beans, Peas.
How long does Onion take to harvest?
Onion takes approximately 110 days from planting to harvest. In Zone 4b, expect your first harvest around Jun 22.
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