Growing Onions in Quebec starts with one number: at 45.47°N (the latitude of Montreal), the longest day of the year delivers 15 hours and 29 minutes of daylight. That’s solidly into long-day territory, with intermediate-day varieties also working well. Short-day onions, the kind sold in many big-box garden sets, are the wrong choice here, they’ll bulb early and stay tiny. Here’s exactly which varieties fit and which don’t.
How long your longest day is
Two numbers decide almost everything about which onion you should plant: the latitude of your garden and the number of daylight hours you get on the longest day of the year. At Montreal’s Pierre Elliott Trudeau International Airport station, that latitude reads 45.47°N. Run through the sunset hour-angle formula with a solar declination of 23.44 degrees at the June solstice, that latitude produces 15 hours and 29 minutes of daylight on the day the sun tops out. (Add roughly seven minutes for atmospheric refraction and the real number is a touch higher, though nobody’s counting that closely in the garden.)
Why does this matter more than temperature? Because an onion bulb isn’t triggered by heat. It’s triggered by day length. Once the plant senses that daylight has crossed its genetic threshold, it stops putting energy into leaves and starts putting it into the bulb. Short-day varieties respond to around 12 hours of daylight, a threshold documented by Clemson Cooperative Extension’s Home & Garden Information Center. Long-day varieties wait for something closer to 14 to 16 hours before they’ll bulb at all.
At 15 hours 29 minutes, Quebec clears the short-day threshold with hours to spare, which is exactly the problem: a short-day onion planted here starts bulbing while the plant is still small and undeveloped, long before it’s built the leaf mass a real onion needs. Long-day varieties, on the other hand, get exactly what they’re waiting for. Intermediate-day types, which typically need somewhere in the 12-to-14-hour range, also do fine at this latitude, several are documented as compatible here.
So the day-length group this territory falls into is long-day, with room for intermediate-day. Short-day is ruled out entirely. That’s the whole page in one paragraph, everything below is detail on top of that fact. For specific cultivar recommendations, see The Best Onion Varieties for Quebec, and for a month-by-month breakdown, see this When to Plant Onions in Quebec guide.
One caution worth repeating: 45.47°N is the latitude of Montreal, not of every backyard in Quebec. The province stretches from farmland well south of the city to territory far above the 55th parallel. A garden near the northern edge of that range gets even more summer daylight than Montreal does, which only reinforces long-day territory, but if you’re gardening near the province’s southern border, or just want to be precise, it’s worth checking your own latitude rather than assuming Montreal’s number applies exactly.
Which varieties bulb in Quebec
Seventeen of the 28 onion varieties documented on this site have a published latitude range that covers 45.47°N, meaning they’re built to bulb reliably at Quebec’s day length. That’s a wide field to choose from, spanning long-day and intermediate-day types:
- Ailsa Craig (long-day, 38-60N)
- Barolo (long-day, 38-55N)
- Blush (long-day, 38-55N)
- Bridger (long-day, 35-50N)
- Frontier (long-day, 40-50N)
- Monastrell (intermediate-day, 35-46N)
- New York Early (long-day, 38-50N)
- Patterson (long-day, 38-55N)
- Powell (long-day, 43-47N)
- Red Long of Florence (intermediate-day, 38-50N)
- Red Long of Tropea (intermediate-day, 35-48N)
- Redwing (long-day, 43-65N)
- Rossa di Milano (long-day, 38-50N)
- Safrane (long-day, 42-50N)
- Scout (intermediate-day, 32-46N)
- Talon (long-day, 42-50N)
- Walla Walla Sweet (long-day, 35-55N)
Six more sit within 1.5 degrees of a published boundary, which puts them in a genuinely blurred zone rather than a clear yes: Cabernet, Calibra, Elsye, Expression, Red Carpet, and Sierra Blanca. These aren’t a flat no. Latitude ranges published by seed sources are a continuum, not a hard cutoff, so a variety listed down to 45N or up to 45N is close enough that it may well perform fine in a Quebec garden. Treat these as an edge case worth trying in a small bed before committing a full row to them, not as a guaranteed bet.
The varieties that will not bulb here
This is the part of the page that matters most if you’ve ever bought a bag of onion sets from a garden center without checking the label. Five varieties documented on this site have published ranges that sit entirely below Quebec’s latitude, which means they simply won’t get the short day length they’re bred for:
- Candy (intermediate-day, 33-40N)
- Gabriella (short-day, 20-35N)
- Madalyn (short-day, 20-35N)
- Red Rock (short-day, 30-36N)
- White Castle (short-day, 30-38N)
Plant any of these in Quebec and here’s the pattern you’ll see: healthy, vigorous green tops all summer, then a bulb that never really forms, because the plant’s cue to stop growing leaves and start swelling never arrived at this latitude. As days shorten toward fall, the plant that never bulbed starts to weaken, and what little bulb it made often rots in the ground or in storage rather than curing properly. If that description matches an onion patch you’ve grown before, it wasn’t a watering or fertilizer problem. It was the wrong variety for the latitude.
When to plant onions in Quebec
Planting timing follows directly from the day-length group established above, and that’s why it differs so much from one part of North America to another. In mild-winter regions, growers plant long-day onions in the fall and let them overwinter as small plants. In Quebec, winters are too harsh for that approach, planting instead runs from late winter (starting seed indoors) through early spring for setting out transplants or sets in the garden.
The frame for that spring window comes from frost data at the MONTREAL/ST-HUBERT A station: the last spring frost falls on average around May 6, and the first fall frost arrives on average around October 5. That gives a frost-free growing season of roughly five months to work with, which is enough time for long-day and intermediate-day onions to size up before the long summer daylight triggers bulbing.
Averages are not safe dates
Both of those frost dates are means calculated from Environment and Climate Change Canada’s 1981-2010 Canadian Climate Normals, not a guaranteed cutoff. By definition, a mean frost date means frost arrives later than that date in roughly half of all years. Treat May 6 as the rough midpoint of a window rather than the day it’s safe to set out young onion plants, and build in a buffer of a week or two on either side depending on how the current season is running.
It’s also worth remembering that a single station reading, even one as central as MONTREAL/ST-HUBERT A, represents one point on a large map. Quebec’s climate varies considerably between the St. Lawrence lowlands and higher or more northern districts, where both the last spring frost and first fall frost can run weeks behind these figures. Gardeners outside the immediate Montreal region should weigh local frost history, not just the regional average, before committing transplants to open ground.