New Jersey · zones 6b–7b
When to plant onions in New Jersey.
Sow or transplant between Feb 5 to Mar 21 in a typical year, keyed to New Jersey's median last frost around Apr 15. A second, fall sowing fits Sep 2 to Oct 14. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical New Jersey season.
1 · Start indoors
Dec 25 to Feb 7
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Feb 5 to Mar 21
Keyed to the ~Apr 15 last frost. Sow 0.5" deep, 4" apart.
Fall round
Sep 2 to Oct 14
Counted back from the ~Oct 28 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
New Jersey spans more than one climate: Zone 7 is the most common zone, but the state runs 6b to 7b. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
New Jersey growing notes
New Jersey onions sit right on the day-length fence.
The Garden State's truck-farm roots still shape the crop
New Jersey earned the nickname Garden State supplying fresh produce to Philadelphia and New York City markets, and onions were part of that trade for generations before supermarkets flattened regional sourcing. That commercial history left behind good bones for home growers: the same intermediate mid-Atlantic climate that made New Jersey onion country in the 1800s still favors a solid bulb today, as long as the variety matches the latitude.
New Jersey sits between roughly 39 and 41 degrees north, the exact band where intermediate-day onions, which need about 12 to 14 hours of daylight to trigger bulbing, perform best. Candy and Superstar both do well here. A true long-day type bred for Minnesota or Michigan needs a summer day length New Jersey's roughly 39 to 41 degree latitude reaches only briefly, if at all, so it risks running out of season before the bulb fully sizes anywhere in the state. Reading the variety tag before buying matters more in this state than in a clear long-day or short-day region, because a mismatched onion here does not fail outright, it just quietly underperforms all season.
Pine Barrens sand against Piedmont clay
South Jersey's Pine Barrens and coastal plain are famously sandy and naturally acidic, often running pH 5.5 or lower, well below the 6.0 to 6.8 onions want. A soil test before planting is worth the 10 dollars; without lime worked in ahead of the season, bulbs stay undersized no matter how well you water and feed them. The upside of that sand is drainage: onions rot fast in standing water, and Pine Barrens ground almost never holds it.
North Jersey runs the opposite problem. Its heavier Piedmont clay and glacial till hold water and nutrients well but compact under foot traffic and drain slowly after a hard rain. Raise the row 4 to 6 inches there and work in compost before planting so onion roots, which sit mostly in the top 6 inches of soil, never sit wet. Either soil type responds to the same test before you commit a whole bed: squeeze a moist handful, and if it packs into a slick ball rather than crumbling, work in compost before onions go anywhere near it.
Downy mildew is the mid-Atlantic humidity tax
New Jersey's humid summers, especially the sticky stretches that roll up from the coast, make downy mildew a bigger threat here than it is in drier onion country farther west. Watch for pale, fuzzy purplish-gray patches on the leaves after a run of damp, overcast days; the disease spreads fastest when foliage stays wet overnight.
Space bulbs a full 4 inches apart so air actually moves between plants, and water the soil directly rather than overhead, ideally in the morning so any splashed leaves dry by afternoon. Pull and discard infected leaves as soon as you spot them instead of waiting for the whole plant to look sick; downy mildew that gets ahead of you here can cut a season short by weeks. The spores overwinter in old plant debris left on the ground, so a clean fall cleanup of the bed does more for next year's onions than any spray applied this season.
In New Jersey: watch for
The pests that find onions here.
A middle-length season, about 196 frost-free days, means onion, bulb overlaps onion thrips for a stretch each summer. Check plants every week or two and treat early.
Silvery streaks and curled leaf tips in hot spells.
Organic fix: Insecticidal soap or neem; hang sticky traps.
Seedlings wilt; white maggots in the bulb base.
Organic fix: Float a row cover over the row; rotate beds each year.
Pale patches with fuzzy gray growth in damp weather.
Organic fix: Space for airflow, water early in the day, spray neem.
White rot
Yellowing and dieback, then wilt; fluffy white mold at the bulb base and roots so rotted the plant lifts straight out.
Organic fix: No cure once it is in the soil. Plant clean stock, never follow onions with onions, and keep infested soil off tools and boots.
Your season math: New Jersey gives onions about 196 frost-free days, and it needs roughly 95 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting onions in New Jersey: questions
When should I plant onions in New Jersey?+
In a typical New Jersey year, sow onions or set out transplants between Feb 5 to Mar 21, keyed to the state's median last frost around Apr 15. There's also a fall window: Sep 2 to Oct 14. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in New Jersey?+
Start seeds inside about 6 weeks before set-out: roughly Dec 25 to Feb 7 for a typical New Jersey season.
What USDA zone is New Jersey?+
New Jersey spans zones 6b–7b, mostly zone 7. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many onions plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.