North Dakota sits at roughly 46.93 degrees north, and on the longest day of the year that latitude delivers 15 hours and 41 minutes of daylight. That number, not the brutal winters the state is known for, is what decides which onions will actually form a bulb here. Long-day varieties are the only sensible bet, joined by a couple of intermediate-day types whose range happens to stretch this far north. Anything bred for southern daylight is off the table, no matter how good it looks on a seed rack.
The short answer for North Dakota
An onion doesn’t bulb because the weather warms up. It bulbs when the number of daylight hours crosses a threshold written into its genetics. At 46.93°N, with 15 hours and 41 minutes of daylight at the June solstice, North Dakota gardens sit well inside long-day territory, the group that needs 14 to 16 hours of daylight before it will stop making leaves and start making a bulb.
Of the varieties documented on this site, 15 have a published range that covers this latitude. Thirteen are classed long-day:
- Ailsa Craig (38-60°N)
- Barolo (38-55°N)
- Blush (38-55°N)
- Bridger (35-50°N)
- Frontier (40-50°N)
- New York Early (38-50°N)
- Patterson (38-55°N)
- Powell (43-47°N)
- Redwing (43-65°N)
- Rossa di Milano (38-50°N)
- Safrane (42-50°N)
- Talon (42-50°N)
- Walla Walla Sweet (35-55°N)
Two more are classed intermediate-day but still list a range that reaches North Dakota’s latitude: Red Long of Florence (38-50°N) and Red Long of Tropea (35-48°N). That’s the working list. Everything else needs a separate look, because a handful of intermediate-day varieties sit right at the edge of usable, and a much longer list simply won’t bulb at all this far north.
What will not work here
Fourteen of the varieties documented on this site have a published upper latitude bound that falls below 46.93°N. Plant one of these in a North Dakota garden and the result isn’t a smaller onion, it’s no onion. The plant reads the long summer days here as a signal it was never built to receive, keeps pushing out leaves past the point where a long-day variety would already be bulbing, and by the time cold weather shuts the season down, there’s a thin neck and a rotting stub where a bulb should be. This is a variety mistake, not a feeding or watering mistake, and no amount of fertilizer fixes it.
- Cabernet (intermediate-day, 35-45°N): upper range ends south of North Dakota
- Calibra (intermediate-day, 35-45°N): same gap, no bulb this far north
- Candy (intermediate-day, 33-40°N): daylight here runs well past its trigger point
- Elsye (intermediate-day, 32-45°N): built for shorter summer days than North Dakota gets
- Expression (intermediate-day, 32-45°N): range stops several degrees south
- Gabriella (short-day, 20-35°N): a southern short-day type, no chance at this latitude
- Madalyn (short-day, 20-35°N): same short-day ceiling, far too low for North Dakota
- Red Carpet (long-day, 40-45°N): long-day, but its range still tops out below the state
- Red Rock (short-day, 30-36°N): a Deep South variety by design
- Red Sensation (short-day, 25-35°N): needs roughly a 12-hour trigger, met here far too early
- Sierra Blanca (intermediate-day, 32-45°N): upper bound south of the reference latitude
- Texas Grano 1015Y (short-day, 25-35°N): a classic short-day onion, wrong hemisphere of the state map for it
- Vidora (short-day, 25-35°North): same story, bulbs on almost no leaf growth up here
- White Castle (short-day, 30-38°N): daylight threshold reached weeks before the plant has size
What changes across North Dakota
The figures above come from a single NOAA reference station, in the southern half of North Dakota, not from the whole state. North Dakota runs from roughly the South Dakota line up to the Canadian border, a spread of a few degrees of latitude, and that’s enough to matter for the varieties sitting closest to the edge of their published range.
| Location | Approx. latitude | What changes |
|---|---|---|
| Southern border area | ~46°N | Daylight on the longest day is close to, but a touch under, 15h41; Monastrell and Scout fall further outside their usable range |
| Reference station | 46.93°N | 15h41 of daylight; solidly long-day country, with Monastrell and Scout sitting right at the outer edge of what’s published for them |
| Northern border area | ~49°N | Daylight runs a little past 15h41; long-day varieties reach full bulb size fastest here, but spring frost dates arrive later too |
Two varieties, Monastrell (intermediate-day, 35-46°N) and Scout (intermediate-day, 32-46°N), fall inside that blurred zone: their published upper bound sits within a degree and a half of the reference latitude. That’s a continuum, not a cliff edge. A gardener at the reference station is right at the line where these two may or may not size up properly; a gardener near the state’s northern border is past it, and should treat Monastrell and Scout as unreliable rather than borderline.
Sweet now, or onions that last
Every onion gardener in North Dakota eventually runs into the same trade-off, and it isn’t a matter of taste, it’s chemistry. The compounds that give an onion its bite are volatile sulfur compounds, and those same compounds are what slow down decay once the onion is out of the ground. University of Missouri Extension puts it plainly: sweet onions do not store as well as pungent ones, because the mildness comes from having fewer of the very compounds that protect the bulb.
That mechanism lines up neatly with day length. Southern gardens, running short-day and intermediate-day varieties, tend to produce sweeter onions that don’t owe the pantry much beyond a few weeks. Northern gardens, running long-day varieties almost exclusively, tend to produce sharper onions that hold up in storage for months. North Dakota’s long-day list reflects that split. Walla Walla Sweet is the outlier built for eating soon rather than keeping long, and it should be treated that way, used up early rather than stacked in a root cellar. Varieties like Redwing, Talon, and Safrane sit at the pungent end of the list, and that pungency is exactly what lets them still be firm and usable in March, months after harvest.
A North Dakota pantry built around long-day onions should look different in late winter than a Georgia or Texas pantry would at the same point. Sweet onions bought or grown in the South are typically gone by then, softened or sprouting. A well-cured, sharp long-day onion from a North Dakota garden can still be sound going into the last weeks of winter, which is the whole reason northern growers keep choosing pungent over mild.
Checking this against your own garden
Everything above is built from one weather station’s numbers, and North Dakota gardens don’t all sit at 46.93°N. Before committing a season’s worth of onion sets or transplants to the long-day list, a few checks are worth five minutes each.
- Look up your own latitude if you’re near the state’s northern or southern edge, since a few degrees shifts which varieties are safely inside range versus borderline
- Confirm your average last spring frost date and first fall frost date with your county extension office rather than a statewide average
- Ask your county extension office, part of the NDSU Extension system, whether any long-day varieties on this list have a known local track record
- If you’re considering Monastrell or Scout, treat them as a trial planting rather than your main crop until you’ve seen how they perform on your own ground
- Note your soil temperature in spring before setting out transplants, since a late, cold spring can push your planting window later than the calendar suggests