When to Plant Onion in Union County, NJ
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.
Union County, New Jersey is in USDA Zone 7a. The average last spring frost is March 29 and the first fall frost is November 12, giving you a growing season of approximately 228 days.
At an elevation of 814 feet, Union County receives approximately 49.4 inches of rainfall annually with predominantly silt loam soil. Summer highs average 93°F, providing good warmth for Onion during the growing season.
Union County Soil Profile
Soil Type
Silt Loam
Soil pH
4.8-6.5
Drainage
Well Drained
Plant Planting Risk Windows
Percentages indicate frost risk at transplant. The 70% safe window means there is a 30% chance of frost after transplant — suitable for cold-hardy crops or gardeners with frost protection. The 90% safe window is best for tender plants.
Plant Water Budget
Onion Planting Timeline — Union County, NJ
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 22 | Feb 22 – Mar 8 |
| Transplant Outdoors | March 29 | Mar 29 – Apr 12 |
| Direct Sow | March 15 | Mar 15 – Apr 5 |
| Fall Sowing | September 3 | Sep 3 – Sep 17 |
| Harvest | June 28 | Jun 28 – Aug 16 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | Start Indoors Transplant Outdoors Direct Sow |
| April | Transplant Outdoors Direct Sow |
| May | — |
| June | Harvest |
| July | Harvest |
| August | Harvest |
| September | Fall Sowing |
| October | — |
| November | — |
| December | — |
Growing Conditions
Sun
Full Sun (6-8+ hours)
Water
Moderate — regular watering
Days to Maturity
90–120 days
Soil pH
6 – 7
USDA Zone
Zone 7a
Growing Season
228 days
Growing Tips for Union County
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
Level Up Your Garden
Onion in Other Locations
Frequently Asked Questions
When should I plant Onion in Union County, NJ?
Union County is in Zone 7a with an average last frost of March 29. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Union County, NJ?
Union County, New Jersey is in USDA Hardiness Zone 7a. The average last spring frost is March 29 and first fall frost is November 12.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Union County gardeners in Zone 7a organize planting dates, track what's growing, and never miss a planting window.
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