When to Plant Onion in USDA Zone 3b
Your May game plan for Zone 3b
Welcome to May in Zone 3b. These are the moves that will have the biggest impact on your growing season.
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Plant out onion
Pinch off the lowest leaves on each seedling before you plant — it reduces water loss while the roots catch up.
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Direct-sow onion
Rake a smooth bed, make a shallow furrow, drop seeds at the spacing on the packet, water gently, walk away.
Looking ahead to June
- Starting indoors: onion
- Fall sowing: onion
Onions are a fundamental kitchen staple available in yellow, white, and red varieties. Choose long-day, short-day, or intermediate types based on your latitude.
In Zone 3b, the average last spring frost is around May 10 and the first fall frost is around September 22, giving you a growing season of approximately 135 days.
Onion Planting Timeline — Zone 3b
Where Is USDA Zone 3b?
The map below highlights the states that contain Zone 3b. Click any state to see the Onion planting schedule for that location.
Onion Planting Calendar — Zone 3b
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 29 | Mar 29 – Apr 12 |
| Transplant Outdoors | May 10 | May 10 – May 24 |
| Direct Sow | May 3 | May 3 – May 24 |
| Harvest | August 9 | Aug 9 – Sep 13 |
| Fall Sowing | June 30 | Jun 30 – Jul 14 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Start Indoors |
| May | Transplant Outdoors Direct Sow |
| June | Fall Sowing |
| July | Fall Sowing |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Free Zone 3b Planting Calendar PDF
Know exactly when to plant every crop in your zone. Get a printable month-by-month calendar customized for Zone 3b with start dates, transplant windows, and harvest times.
Growing Conditions
Sun
Full Sun (6-8+ hours)
💧 Water
Moderate — regular watering
Days to Maturity
90–120 days
Soil pH
6 – 7
Zone Temperature Range
°F to °F average annual minimum
Growing Season
135 days (Zone average)
Planting Specifications
| Planting Depth | 1 inches |
| Plant Spacing | 6 inches apart |
| Row Spacing | 12 inches between rows |
Growing Tips for Onion in Zone
Zone has a short growing season (~135 days). Start Onion indoors early and use season-extension techniques like row covers and cold frames.
Start seeds indoors 8-10 weeks before transplanting. Match day-length type to your latitude. Stop watering when tops begin to fall over and cure bulbs for 2-3 weeks before storage.
Companion Planting
Good Companions
Avoid Planting Near
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Saving Onion Seeds
Recommended for Your Garden
Start seeds indoors with reusable cell trays and humidity domes.
Test your soil pH, nitrogen, phosphorus, and potassium levels before planting.
Keep your garden organized with durable, weather-resistant plant labels.
Related Plants
Onion in Other Zones
Onion by State
- Alabama
- Alaska
- Arizona
- Arkansas
- California
- Colorado
- Connecticut
- Delaware
- Florida
- Georgia
- Hawaii
- Idaho
- Illinois
- Indiana
- Iowa
- Kansas
- Kentucky
- Louisiana
- Maine
- Maryland
- Massachusetts
- Michigan
- Minnesota
- Mississippi
- Missouri
- Montana
- Nebraska
- Nevada
- New Hampshire
- New Jersey
- New Mexico
- New York
- North Carolina
- North Dakota
- Ohio
- Oklahoma
- Oregon
- Pennsylvania
- Rhode Island
- South Carolina
- South Dakota
- Tennessee
- Texas
- Utah
- Vermont
- Virginia
- Washington
- West Virginia
- Wisconsin
- Wyoming
Frequently Asked Questions
When should I plant Onion in Zone 3b?
In Zone 3b, plan your Onion planting around the average last frost date of May 10. Start seeds indoors around March 29. Direct sow outdoors around May 3. Transplant seedlings around May 10.
Can Onion grow in Zone 3b?
Yes, Onion can grow well in Zone 3b, hardy in USDA zones 3a through 10b. Zone 3b has a growing season of approximately 135 days, which is sufficient for Onion (90-120 days to maturity).
When can I harvest Onion in Zone 3b?
In Zone 3b, expect to harvest Onion from August 9 – September 13. Onion takes 90-120 days from planting to harvest.
What is the last frost date for Zone 3b?
The average last spring frost in Zone 3b is around May 10, and the first fall frost is around September 22. This gives a growing season of approximately 135 days. These are 50% probability dates — actual frost dates vary year to year.
What should I plant next to Onion?
Good companion plants for Onion include Carrots, Lettuce, Beets, Cabbage. These companions can help with pest control, pollination, and nutrient sharing.
Your Free Printable Garden Planner
A 24-page printable planner tailored to your zone. Planting dates, monthly task lists, harvest log, seed inventory, and succession charts — everything you need to plan a full season.