Wyoming sits at 41.15 degrees north, the latitude of Cheyenne, and gets 14 hours and 58 minutes of daylight on the summer solstice. That’s the long-day zone. The varieties that will actually make a bulb here are long-day and intermediate-day types, and several of the popular short-day sets sold everywhere else simply won’t work at this latitude.
The short answer for Wyoming
Onions don’t bulb because of heat. They bulb because of day length, and the trigger is different for every variety group. Short-day onions start bulbing once the day reaches about 12 hours of light, which happens early in the season across most of the country. Long-day onions wait for something closer to 14 to 16 hours before they’ll switch from making leaves to making a bulb. At Cheyenne’s latitude, the longest day of the year hits 14 hours 58 minutes, comfortably inside the window that long-day varieties need and just enough for many intermediate-day types too.
That single number, 14h58m, is why Wyoming gardens belong to the long-day group with intermediate-day varieties filling in at the margins. Nineteen of the varieties documented on this site have a published range that covers 41.15N, and they split into two working groups.
The long-day options include Ailsa Craig, Barolo, Blush, Bridger, Frontier, New York Early, Patterson, Red Carpet, Rossa di Milano, and Walla Walla Sweet. The intermediate-day options include Cabernet, Calibra, Elsye, Expression, Monastrell, Red Long of Florence, Red Long of Tropea, Scout, and Sierra Blanca. Any of these nineteen are a reasonable bet for a garden at Cheyenne’s latitude, and most of the state falls close enough to that line that the same list applies.
Three more varieties sit close enough to a published boundary that they land in a genuine gray zone rather than a clear yes. Candy (intermediate-day, rated 33-40N) is just past its usual upper limit here. Safrane and Talon (both long-day, rated 42-50N) sit just below their usual lower limit. All three may bulb fine in a Wyoming garden, particularly one at the northern end of the state, but a gardener planting them at Cheyenne’s exact latitude is working at the edge of the published range rather than in the middle of it.
What will not work here
Planting the wrong day-length group in Wyoming doesn’t produce a smaller crop. It produces two very different failures, and neither one is a feeding problem or a watering problem. It’s a variety problem, decided the day the seed went in the ground.
Short-day onions planted this far north hit their 12-hour bulbing trigger while the plant is still young and small. The bulb forms on schedule, but the plant hasn’t had time to build the leaf mass that would have made it a decent-sized onion. The result is a small, immature bulb, not a delayed one. Seven varieties documented on this site fall into that category for Wyoming:
- Gabriella (short-day, 20-35N) — bulbs at roughly 12 hours, far too early at 41N latitude
- Madalyn (short-day, 20-35N) — same early trigger, small bulbs guaranteed
- Red Rock (short-day, 30-36N) — still well south of Wyoming’s daylight range
- Red Sensation (short-day, 25-35N) — bulbs before the plant has size to spare
- Texas Grano 1015Y (short-day, 25-35N) — a Gulf Coast variety, wrong latitude entirely
- Vidora (short-day, 25-35N) — same early-trigger problem
- White Castle (short-day, 30-38N) — closest of the seven, still below Wyoming’s range
The opposite failure happens at the other end of the spectrum, and it’s worse because there’s no small onion at all. Two long-day varieties published for latitudes above 41.15N, Powell (43-47N) and Redwing (43-65N), need more daylight than Cheyenne’s summer ever provides. Plant either one at that latitude and the day length never reaches the trigger point. The plant keeps making leaves all season, never switches to bulbing, and eventually rots in the ground or in storage with nothing but a swollen stem to show for it. That’s a variety mismatch, not a growing mistake, and no amount of fertilizer fixes it.
What changes across Wyoming
Cheyenne, where the 41.15N figure comes from, sits at Wyoming’s southern edge. The state’s border runs from that line up to roughly 45 degrees north near the Montana line, which puts towns like Sheridan and Cody several degrees further north than the reference city the numbers above are built on. That gap matters, because those extra degrees of latitude buy real daylight in June.
A garden near the northern border gets noticeably more summer daylight than Cheyenne does, enough to move the two “will not bulb here” varieties from the failure list into the workable list. Powell and Redwing are rated for 43-47N and 43-65N respectively, and northern Wyoming sits inside both ranges even though southern Wyoming does not. The same shift pulls Safrane and Talon, the two blurred long-day varieties rated 42-50N, solidly into range rather than leaving them at the edge.
| Location | Latitude | What it changes |
|---|---|---|
| Cheyenne (reference city) | 41.15°N | Baseline: long-day and intermediate-day varieties work; Powell and Redwing will not bulb; Safrane and Talon are borderline |
| Northern Wyoming (near the Montana line) | ~45°N | More summer daylight; Powell and Redwing become workable; Safrane and Talon move out of the gray zone |
A gardener in Sheridan or Cody isn’t wrong to try varieties that a Cheyenne gardener should avoid. They’re simply gardening under a different day-length ceiling, four degrees of latitude away from the number this page is built on.
Sweet now, or onions that last
Every onion variety that will bulb in Wyoming falls somewhere on a spectrum between sweet and short-lived on one end, and sharp and long-keeping on the other. That’s not a marketing distinction. It’s chemistry. The volatile sulfur compounds that make an onion bite back when you slice it raw are the same compounds that protect the bulb from breaking down in storage. Fewer of those compounds means a milder onion on the cutting board and a shorter shelf life in the pantry. More of them means the opposite trade.
Because Wyoming sits in the long-day zone rather than the short-day zone further south, the state’s growing conditions already lean toward the pungent, long-keeping end of that spectrum compared to states below the 35th parallel. Within the varieties that work here, though, the same trade-off still plays out. Walla Walla Sweet and Candy sit at the milder end of the list, better eaten within a few weeks of harvest than stashed away for winter. The more work-a-day long-day storage types, varieties like Bridger, Patterson, and Frontier, trade some of that mildness for onions that hold up in a root cellar or a cool basement well past the first snow.
A Wyoming gardener who wants onions on hand in March is better served planting toward the sharper end of the list. One who wants a milder onion to slice fresh in August can lean toward Walla Walla Sweet or Candy and simply plan to use that crop up early, rather than counting on it to outlast the winter.
Checking this against your own garden
The 41.15N figure and the 14h58m of summer daylight both belong to Cheyenne specifically, not to every backyard in Wyoming. A garden near the state’s northern edge is working with a meaningfully longer summer day, and that shifts which varieties are safe bets versus which ones are still gambles. Before ordering onion sets or starts, it’s worth confirming a few things locally rather than relying on a single statewide number.
- Look up your own latitude if you’re not near Cheyenne, especially if you garden in the northern third of the state
- Check your local average last and first frost dates, since onion transplants go in weeks before the frost-free date in most of Wyoming
- Call or check the website of your county extension office for planting-date guidance specific to your elevation and microclimate
- If you’re trying Safrane, Talon, or Candy, treat the first season as a test rather than a sure thing
- Note your garden’s elevation, since higher ground in the same latitude band often runs a shorter, cooler season than the valley floor
The University of Wyoming Extension system keeps county-level planting calendars that account for elevation differences the statewide latitude figure can’t capture on its own.