Vermont sits at a latitude where long summer daylight, not summer heat, decides whether an onion bulbs at all. At 44.47 degrees north, the reference point for this state’s climate data, the longest day of the year brings 15 hours and 22 minutes of daylight. That number rules out most of the onion world and narrows the choice to a specific group of varieties bred to wait for exactly this much light before they start forming a bulb.
The short answer for Vermont
Vermont is long-day onion territory, full stop. Long-day varieties need 14 to 16 hours of daylight before they switch from making leaves to making a bulb, and Burlington’s 15 hours 22 minutes on the summer solstice falls comfortably inside that window. That’s the trigger mechanism, and it has nothing to do with how warm or cool the growing season runs.
Among the 23 varieties documented on this site whose published range covers 44.47N, the long-day group gives Vermont gardeners the most room to work with: Ailsa Craig, Barolo, Blush, Bridger, Frontier, New York Early, Patterson, Powell, Red Carpet, Redwing, Rossa di Milano, Safrane, Talon, and Walla Walla Sweet all list Vermont’s latitude squarely within their range.
Intermediate-day varieties also work here, since their published ranges stretch far enough north to include 44.47N: Cabernet, Calibra, Elsye, Expression, Monastrell, Red Long of Florence, Red Long of Tropea, Scout, and Sierra Blanca can be grown in Vermont without the bulbing problems that show up further south. What they trade for that flexibility is a shorter storage life than the true long-day types, a point worth keeping in mind before choosing what to plant.
Two varieties, Powell (43-47N) and Redwing (43-65N), sit near the top of the pack in terms of how far north their range extends, which matters if you garden closer to the Canadian border than to Burlington.
What will not work here
Short-day onions are built for the opposite kind of daylight problem. They start bulbing once day length hits roughly 12 hours, a threshold Vermont blows past before the plants have had any real time to grow leaves. The result isn’t a smaller harvest, it’s a failed one: the plant bulbs prematurely at a fraction of its potential size, then the foliage collapses and the bulb rots in the ground before it’s worth pulling. Planting a short-day onion in Vermont is a variety mistake, not a feeding or watering mistake, and no amount of fertilizer fixes it.
Eight varieties documented on this site fall into that trap for this latitude, either because they’re short-day types or because their range simply doesn’t stretch this far north:
- Candy (intermediate-day, 33-40N): range tops out well south of Vermont, too far south to bulb properly here
- Gabriella (short-day, 20-35N): bulbs at 12 hours of daylight, far too early for a Vermont summer
- Madalyn (short-day, 20-35N): same short-day trigger, gives tiny bulbs before the plant matures
- Red Rock (short-day, 30-36N): built for southern latitudes, not this far north
- Red Sensation (short-day, 25-35N): premature bulbing, undersized harvest
- Texas Grano 1015Y (short-day, 25-35N): a Gulf Coast onion, wrong daylight trigger for New England
- Vidora (short-day, 25-35N): same short-day mechanism, same failure here
- White Castle (short-day, 30-38N): range stops well short of Vermont’s latitude
Plant any of these in Vermont soil and the season plays out the same way: leafy growth through spring, a premature and undersized bulb once daylight crosses the 12-hour mark in early summer, and rot setting in from there. None of these varieties have a page of their own on this site because they’re not options for this territory, though Gabriella, Madalyn, Red Rock, and White Castle are worth naming so gardeners recognize them if they show up in a seed catalog.
What changes across Vermont
Vermont runs roughly 150 miles from its southern border near Massachusetts to its northern edge along Quebec, which translates to a latitude span of a little over two degrees, from around 42.7N in the south to about 45.0N in the north. Burlington, the reference city behind the 44.47N figure and the 15-hour-22-minute daylight number, sits toward the northern half of that range, closer to the Canadian border than to the Massachusetts line.
That spread matters less for onions than it would for a crop with a narrower window, because long-day varieties tolerate a wide band of daylight hours. Still, the difference shows up at the margins of the variety list.
| Location | Approximate latitude | Daylight vs. Burlington | What it changes |
|---|---|---|---|
| Northern Vermont (near Quebec border) | ~45.0N | Slightly longer | Top-end long-day varieties like Redwing (43-65N) fit comfortably; no variety change needed from the Burlington list |
| Burlington (reference city) | 44.47N | 15h 22m (baseline) | Full long-day list applies as written above |
| Southern Vermont (near Massachusetts border) | ~42.7N | Slightly shorter | Still solidly long-day territory; intermediate-day varieties have a bit more margin to fully mature before bulbing |
A gardener in Bennington or Brattleboro isn’t gardening in a different onion zone than one in Burlington or St. Albans. The whole state falls within long-day country. The main thing that shifts at the southern edge is that intermediate-day varieties gain a slightly wider comfort margin, while at the northern edge the longest-range long-day varieties, Redwing in particular, have the most room to spare.
Sweet now, or onions that last
Every onion variety carries a trade-off, and it comes down to chemistry rather than luck. The volatile sulfur compounds that give an onion its bite are the same compounds that protect it in storage. A variety with fewer of them tastes milder and sweeter raw, but it breaks down faster in the pantry. A variety loaded with them brings tears to your eyes at the cutting board and then sits in a mesh bag through the winter without going soft. University of Missouri Extension puts it plainly: sweet onions do not store as well as the more pungent types.
Vermont’s long-day territory leans toward the pungent, long-keeping end of that spectrum, which is generally good news for a state with a long, cold winter and a short growing season. Varieties like Talon, Frontier, and Patterson fall into that storage-onion camp: sharper on the cutting board in August, still firm in the root cellar in March. Walla Walla Sweet sits at the other end, prized for its mild flavor but not built to outlast the season it’s harvested in.
The practical question for a Vermont gardener isn’t which variety is “better,” it’s what you want your pantry to look like in three or four months. A bed planted entirely in sweet, mild long-day types gives you onions worth eating fresh through late summer and early fall, and not much after that. A bed weighted toward the sharper, higher-sulfur varieties gives you less immediate reward at the table but a supply that carries into the depths of a Vermont winter, when the root cellar is doing more work than the garden.
Checking this against your own garden
The 44.47N figure and the 15-hour-22-minute daylight number both belong to Burlington specifically, not to every corner of Vermont. If you garden near the Canadian border or down near the Massachusetts line, the numbers shift slightly in either direction, though as the table above shows, the shift isn’t large enough to change which onion group you should plant.
What does vary meaningfully across the state is frost timing, soil temperature in spring, and how early the ground is workable, none of which are captured by a single latitude figure. Before finalizing a variety list, a few checks are worth doing on your own:
- Look up your own latitude if you’re more than 30 or 40 miles from Burlington, using any online coordinate finder
- Check your local average last frost date, since that determines when transplants or sets go in the ground
- Contact your county’s University of Vermont Extension office for soil test recommendations specific to your garden
- Confirm whether the variety you’re considering is sold as sets, transplants, or seed, since that changes your planting timeline even after the variety question is settled
- Note your microclimate: a south-facing slope or a low frost pocket can shift your effective planting window by a week or two regardless of what the state-wide averages say
A latitude figure tells you which day-length group to plant. It doesn’t replace what your own soil, slope, and frost dates will tell you once the season actually starts.