New York · zones 5a–7b
When to plant onions in New York.
Sow or transplant between Feb 20 to Apr 5 in a typical year, keyed to New York's median last frost around Apr 30. A second, fall sowing fits Aug 23 to Oct 4. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical New York season.
1 · Start indoors
Jan 9 to Feb 22
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Feb 20 to Apr 5
Keyed to the ~Apr 30 last frost. Sow 0.5" deep, 4" apart.
Fall round
Aug 23 to Oct 4
Counted back from the ~Oct 18 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
New York spans more than one climate: Zone 7 is the most common zone, but the state runs 5a 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 York growing notes
Onion bulbing here runs on day length, not warmth, and New York's latitude puts the whole state in long-day territory, where a short-day variety bred for southern gardens bulbs early and small.
A trigger that has nothing to do with the weather
Onion transplants go into New York soil shallow, about a half inch deep, spaced a tight 4 inches apart, taking a full 95 days to size into a storage bulb. Most of that growth looks like leaf-building, and it's tempting to assume warmth or size triggers bulbing. It doesn't. An onion tracks day length through its leaves and commits to bulbing only once that length crosses the point its variety was bred for; soil temperature, fertilizer, and plant size don't move that trigger. A well-grown bulb here still averages only about half a pound at harvest, modest enough that an undersized bulb barely counts as a harvest.
That mechanism splits onion varieties by latitude. A long-day type needs the long daylight hours a northern summer provides, and this state delivers that everywhere in it; latitude decides day length, not hardiness zone, so this is one decision that doesn't shift by zone. A short-day type, bred for a Georgia or Texas spring where days never run that long, hits its shorter trigger here within weeks of germinating, while the plant still carries only a handful of leaves. The bulb it forms is real, just small, since bulb size tracks leaf size at bulbing. A Vidalia-style sweet onion from a seed catalog is the classic short-day trap; Patterson and other long-day types are the safer choice.
Two starts, and a rule that doesn't change between them
New York onion growers work from two different starts. The standard route sets transplants out in spring once the ground can be worked, giving the plant lengthening days to build leaves before the long-day trigger arrives. The other route sets a hardier planting out in late summer, small enough to overwinter as little more than a seedling, then resumes growing at the first thaw with a head start a spring-set plant never gets, though it asks that young planting to survive winter first, a bigger ask inland than near the coast.
Whichever start a grower chooses, the trigger itself doesn't move; both wait for the same long summer days. What changes is how much leaf is already built once it arrives, which is why a surviving fall planting can bulb earlier. A loose mulch laid over the row once the ground has frozen solid, not by a date on the calendar, carries a young planting through the cold months, and that route runs less risk near Long Island than toward the North Country.
Thrips in the neck, maggots at the base, and a rot that doesn't leave
Onion thrips are easy to miss; the damage, a silvery, papery streaking low on the leaf, reads as sun scorch at a glance. Check the V where a new leaf meets the neck, where thrips cluster and hide. A drought-stressed planting draws heavier thrips numbers than a watered one, so steady watering in dry spells helps. Onion maggot hits earlier and lower: flies lay eggs at the base of young transplants, and a wilting seedling that pulls loose with barely any root is the tell. A floating cover over the bed for the first couple weeks keeps the flies off entirely.
Downy mildew shows first as pale, oblong patches, then a fuzzy gray-purple growth during humid, overcast weather, spreading fastest where leaves crowd, staying damp between rains. Pull an infected plant the moment that fuzz shows, before it sheds spores on its neighbors. White rot deserves the most caution: a soil fungus that girdles the bulb's base in white, cottony growth and survives in the ground for years, with no practical way to clear it. A bed that loses plants to it is worth keeping out of onions and garlic for years afterward, since the same fungus feeds on either crop.
In New York: watch for
The pests that find onions here.
A middle-length season, about 171 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 York gives onions about 171 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 York: questions
When should I plant onions in New York?+
In a typical New York year, sow onions or set out transplants between Feb 20 to Apr 5, keyed to the state's median last frost around Apr 30. There's also a fall window: Aug 23 to Oct 4. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in New York?+
Start seeds inside about 6 weeks before set-out: roughly Jan 9 to Feb 22 for a typical New York season.
What USDA zone is New York?+
New York spans zones 5a–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.