Practical planning tools for short growing seasons.
Climate-based onion planting guide for Sept-Îles, Quebec
When to Plant Onions in Sept-Îles
Onions are more marginal in Sept-Îles because the season is workable but not roomy. Timing, variety speed, and warm placement usually need to be part of the plan.
Typical Planting Window
Borderline in this climate
Use the planting dates below for onions in Sept-Îles.
Start indoors
March 22
Typical planting windowMay 17 – May 31
MethodTransplant
Typical days to maturity95–110
Onions are usually started indoors around March 22 and planted outdoors during the normal local window of May 17 to May 31.
Most varieties need about 95–110 days to reach maturity once they are in the garden.
Onions are possible in Sept-Îles, though this is the kind of crop where the margin is narrow enough that small choices start to matter a lot.
Compared with many Quebec locations, Sept-Îles usually reaches the planting season for onions a bit later.
Best local strategy:
Start early, plant on time, and lean toward faster varieties in the warmest spots you have.
Can Onions Mature in Sept-Îles?
Growing degree days measure how much useful warmth typically accumulates during the season. For onions, this helps estimate whether local heat accumulation is usually enough for the crop to reach maturity on time.
Available GDD (base 45)1109
Typical crop GDD target1300
Heat margin-191
From the usual planting window, Sept-Îles typically provides about 1109 growing degree days for onions. With a typical crop target of 1300, that leaves a heat margin of -191. That narrow heat margin means small delays or slower varieties can quickly reduce the odds of timely maturity.
When Is It Too Late to Plant?
When planting later than usual, this table shows how much growing degree day heat is still available from each point in the season. As planting gets pushed back, the remaining heat drops and the crop becomes less likely to mature on time.
Checkpoint
Remaining GDD
Heat margin
Fit vs typical target
Apr 15
1154
-146
Usually short
Jun 1
1135
-165
Usually short
Jun 15
1054
-246
Usually short
Jul 1
901
-399
Usually short
How Different Onion Varieties Affect Results
In Sept-Îles, very early and early onion varieties are usually the safest choice because they leave the least room for the season to turn against you. Slower classes are much less forgiving here.
Varieties that often fit well here include:
Walla Walla
— large and popular, but still best when started early enough to build size
Best Onion Varieties for Sept-Îles
Very early onion varieties are usually the strongest all-around match in Sept-Îles. The local season can support onions, so the main choice is usually about bulb size, sweetness, color, and keeping quality.
June 7
local season starts
September 13
frost pressure returns
Less heat used1109 GDD available
Hover or tap the dots to see which recommended varieties use that much local heat.
For Sept-Îles, start with Walla Walla for onions when you want large sweet onions.
Compare each variety’s heat need and maturity timing against the local frost-free window before choosing what to grow.
Recommended starting point
Walla WallaVery early
1100 GDD needed1109 available before frost
June 7September 13
Tight fit
Why this fit?
Local season fit:
Walla Walla leaves about 9 GDD cushion against the normal Sept-Îles crop heat estimate.
Best for: large sweet onions.
A large, popular onion that can be rewarding, but still needs an early enough start to build size.
Tradeoff: Needs an early enough start to build size.
GDD comparisons are a planning shortcut, not a guarantee. Soil, watering, sowing depth, pests, transplant quality, and harvest goals still affect the final result.
Varieties that didn’t make the cut
These varieties are not the main picks for Sept-Îles because they either run past the normal season or leave too little margin before frost.
ailsa craigLate
Needs1400 GDD
Sept-Îles gives1109 GDD
Gap
291 GDD short
1109 GDD available before frost291 more GDD needed
June 7September 13
Runs past season
Why not a main pick?
Local season fit:
ailsa craig usually needs about 291 more GDD than Sept-Îles provides before frost.
Best for: large exhibition onions.
A large onion that is more exposed in shorter seasons because it benefits from a longer finishing run.
Tradeoff: More exposed in shorter seasons.
pattersonMid-season
Needs1300 GDD
Sept-Îles gives1109 GDD
Gap
191 GDD short
1109 GDD available before frost191 more GDD needed
June 7September 13
Runs past season
Why not a main pick?
Local season fit:
patterson usually needs about 191 more GDD than Sept-Îles provides before frost.
Best for: long-keeping onions.
A solid keeping onion that wants enough runway to size up well before the season closes.
Tradeoff: Needs enough runway before the season closes.
redwingMid-season
Needs1300 GDD
Sept-Îles gives1109 GDD
Gap
191 GDD short
1109 GDD available before frost191 more GDD needed
June 7September 13
Runs past season
Why not a main pick?
Local season fit:
redwing usually needs about 191 more GDD than Sept-Îles provides before frost.
Best for: red storage onions.
A strong red onion that makes sense where the season is supportive enough for good bulb sizing.
Tradeoff: Needs a supportive season for good bulb sizing.
copraEarly
Needs1200 GDD
Sept-Îles gives1109 GDD
Gap
91 GDD short
1109 GDD available before frost91 more GDD needed
June 7September 13
Runs past season
Why not a main pick?
Local season fit:
copra usually needs about 91 more GDD than Sept-Îles provides before frost.
Best for: dependable storage onions.
A practical storage onion with good all-around usefulness when started early.
Tradeoff: Still needs enough season to size up.
Variety class
Typical days to maturity
Typical GDD need
Local fit
Very early
90–95
1100
Tight
Early
95–105
1200
Tight
Mid-season
105–115
1300
Poor fit
Late
115–120
1400
Poor fit
Main risk: This is close enough that any delay in planting, or any extra days to maturity, can be the difference between finishing and falling short before frost.
How Frost Affects Planting Dates for Onions in Sept-Îles
Sept-Îles usually has about 98 frost-free days, with a typical last spring frost around June 7 and a typical first fall frost around September 13.
Typical last spring frostJune 7
Typical first fall frostSeptember 13
Typical frost-free days98
Minimum safe temperature28°F /
-2
°C
Onions are generally
lightly frost tolerant
and temperatures below about 28°F (
-2
°C) can slow growth or damage plants.
Onions are usually tolerant enough of cool conditions that frost dates act more like planning markers than hard limits. In practice, timing and steady early growth matter more than avoiding every light frost.
The most common problem is running short on season. Late planting, slower varieties, and cooler exposed sites can turn a possible crop into a disappointing one.
In Sept-Îles, the seasonal margin for onions is tighter before the usual fall frost around September 13, which makes local site warmth more important than it is for easier crops. Local gardens do not all warm and cool at the same pace. The warmest garden spots are usually south-facing walls, sheltered gardens, raised beds, and sunnier urban lots. Cooler spots like low spots, exposed sites, and shadier yards tend to warm up later and usually provide less heat. For onions, warmer garden spots usually improve early growth and can make timing a little more forgiving.
Protect onions with strong starts and steady moisture
The useful setup is about strong early growth, steady moisture, and getting the crop to a clean finish.
Soil and planting setup
For storage crops, the best gains usually come from strong early growth and a clean finish.
