Newark sits at 40.68 degrees north, and on the longest day of the year it gets 14 hours and 55 minutes of daylight. That single number decides which onions will actually bulb in a New Jersey garden. It rules out the short-day sets sold in most big-box stores, and it puts the state squarely in long-day and intermediate-day territory. Here’s what that means for your rows this year.
How long your longest day is
Everything on this page comes back to that one figure: 14 hours and 55 minutes of daylight at the June solstice, measured for the reference station near Newark (USW00014734), at 40.68 degrees north latitude. An onion doesn’t care how hot your July is. It cares how long the sun stays up, because day length is the trigger that tells the plant to stop building leaves and start building a bulb. Clemson Cooperative Extension’s Home & Garden Information Center puts the bulbing threshold for short-day types at around 12 hours of daylight. Long-day varieties wait much longer, typically 14 to 16 hours, and intermediate-day types sit in between, around 12 to 14 hours.
At almost 15 hours on the longest day, New Jersey clears the short-day threshold easily, and it clears most of the intermediate-day range too. That puts long-day and intermediate-day onions squarely in play here. Short-day onions, the kind that dominate grocery store onion sets and mail-order collections, are built for latitudes far to the south, where summer days never stretch past 12 or 13 hours. Plant one of those in a New Jersey backyard and the day length arrives too early. The bulb starts forming before the plant has grown enough leaf mass to feed it, so you end up with a small onion, or sometimes just a green top and a thin neck where a bulb should be.
Why your own backyard might differ
New Jersey isn’t a single point on a map. The state runs from roughly 38.9 degrees north near Cape May to about 41.4 degrees near the New York border, a spread of more than two degrees of latitude. That’s not huge compared to a state like California or Texas, but it’s enough to matter at the margins. A gardener near the southern tip of the state gets slightly less summer daylight than Newark; someone up near the High Point area gets slightly more. If you’re gardening near either edge of New Jersey, it’s worth checking your own coordinates against a daylight calculator rather than assuming Newark’s numbers apply exactly to you. For most of the state, though, the Newark figures are a solid working reference.
Which varieties bulb in New Jersey
Out of the varieties documented on this site, 19 have a published latitude range that covers 40.68 degrees north, meaning they’re built to bulb reliably at New Jersey’s day length. Both long-day and intermediate-day types show up on this list, which gives gardeners here more flexibility than states further south or further north.
- Long-day: Ailsa Craig, Barolo, Blush, Bridger, Frontier, New York Early, Patterson, Red Carpet, Red Long of Florence, Rossa di Milano, Walla Walla Sweet
- Intermediate-day: Cabernet, Calibra, Elsye, Expression, Monastrell, Red Long of Tropea, Scout, Sierra Blanca
Three more varieties, Candy, Safrane, and Talon, fall within 1.5 degrees of a published boundary, which puts them in a blurred zone rather than a clear yes. Candy’s range runs 33 to 40 degrees north, just short of Newark’s 40.68; Safrane and Talon both start at 42 degrees, just above it. These may bulb here, but you’re gardening at the edge of what the catalog data supports, not in the middle of it. Treat them as an experiment, not a guarantee.
The varieties that will not bulb here
This is the list that actually saves a season. Four varieties are published for latitudes below New Jersey and simply won’t work here: Gabriella, Madalyn, Red Rock, and White Castle. All four are short-day types bred for the Gulf Coast and the Deep South. Planted in a New Jersey garden, the day length arrives while the plants are still small, so the bulbs form early and stay tiny. This is the classic story behind a bag of grocery-store onion sets that produced a handful of golf-ball onions and a lot of green tops. It’s not a feeding mistake or a watering mistake. It’s the wrong variety for the wrong latitude.
Two more varieties fail in the opposite direction: Powell and Redwing, both published for latitudes above New Jersey (43 to 47 and 43 to 65 degrees north, respectively). These need more summer daylight than New Jersey ever provides. The result isn’t a small onion, it’s no onion at all. The plant keeps making leaves all season, waiting for a day length that never arrives, and eventually the foliage collapses and the bulb, such as it is, rots in the ground. If you’ve ever pulled up a patch of healthy-looking onion tops in October only to find mush underneath, this is very likely why.
When to plant onions in New Jersey
Because New Jersey sits in long-day and intermediate-day territory, the planting calendar looks different than it does in the Deep South, where short-day onions get tucked into the ground in autumn and overwinter as small plants. Here, onions go in during late winter to early spring, timed around the last spring frost rather than the first fall frost.
At the Newark reference station, the last spring frost typically falls between March 29 and April 6, based on NOAA’s 1991-2020 climate normals for 32-degree freeze probabilities. Onion transplants and sets can go in a few weeks ahead of that date, since young onion plants tolerate a light frost far better than tender summer crops do. The first fall frost at the same station runs from November 4 to November 16, which matters less for planting and more for knowing when to expect your foliage to finally die back if you’re growing a late storage crop.
Averages, not promises
Those frost windows come from one weather station, an airport, and airport sites tend to run warmer than the surrounding suburbs and countryside. Suburban and rural gardens across New Jersey commonly see their last spring frost arrive later, and their first fall frost arrive earlier, sometimes by one to two weeks, with the gap widening at higher elevations in the northwest part of the state. Treat the Newark dates as a starting frame, not a guarantee for your own yard. Local Rutgers Cooperative Extension county offices can offer county-level frost data that will fit your garden than a statewide figure ever will.
Sweet onions or onions that keep
Every onion grower eventually runs into the same trade-off: the mild, sweet onions that taste great sliced raw on a burger are also the ones that turn soft and sprout in the pantry by January. According to University of Missouri Extension, “as a rule, ‘sweet’ onions do not store as well as the more pungent types.” That’s not a marketing quirk. It’s chemistry. The sharp bite of a pungent onion comes from volatile sulfur compounds, and those same compounds happen to be part of what protects the bulb during long storage. Breed the sulfur down for sweetness, and you also breed away some of the storage life.
This lines up with the day-length pattern too. Short-day varieties, grown further south, tend to run sweeter and store for a shorter window. Long-day varieties, grown further north, tend to run more pungent and keep for months. New Jersey’s mix of long-day and intermediate-day options puts local gardeners in a middle ground: onions here won’t be as flatly sweet as a Vidalia-style Southern crop, but many of the long-day varieties on the list above, Ailsa Craig, Patterson, and Walla Walla Sweet among them, will store reasonably well into winter if cured and kept properly.
What this means for your own kitchen: don’t expect a single crop to do both jobs. If you want onions to eat fresh through late summer and early fall, lean toward the milder end of the varieties that bulb here. If you want a pantry that’s still stocked in March, favor the more pungent long-day types and cure them thoroughly before storage, since a sweeter variety planted with storage in mind will simply not last, no matter how carefully it’s cured.