Practical planning tools for short growing seasons.
Climate-based onion planting guide for Yellowknife, Northwest Territories
When to Plant Onions in Yellowknife
Onions are possible in Yellowknife, though this is the kind of crop where planning details matter much more than they do for easier crops.
Typical Planting Window
Borderline in this climate
Use the planting dates below for onions in Yellowknife.
Start indoors
March 8
Typical planting windowMay 3 – May 17
MethodTransplant
Typical days to maturity95–110
Onions are usually started indoors around March 8 and planted outdoors during the normal local window of May 3 to May 17.
Most varieties need about 95–110 days to reach maturity once they are in the garden.
Onions can still succeed in Yellowknife, but the crop usually needs better-than-average planning around timing, variety speed, and site warmth.
This is a crop where the local season can work, though it leaves limited room for delayed starts or weaker placement.
Best local strategy:
Protect as much early momentum as possible and pair the crop with warm placement and realistic variety choice.
Can Onions Mature in Yellowknife?
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)1187
Typical crop GDD target1300
Heat margin-113
From the usual planting window, Yellowknife typically provides about 1187 growing degree days for onions. With a typical crop target of 1300, that leaves a heat margin of -113. 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
1187
-113
Usually short
Jun 1
1175
-125
Usually short
Jun 15
1085
-215
Usually short
Jul 1
900
-400
Usually short
How Different Onion Varieties Affect Results
In Yellowknife, very early onion varieties are usually the most dependable choices, while early types sit closer to the line when planting is delayed or the season is less forgiving.
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 Yellowknife
Very early onion varieties are usually the strongest all-around match in Yellowknife. The local season can support onions, so the main choice is usually about bulb size, sweetness, color, and keeping quality.
May 24
local season starts
September 21
frost pressure returns
Less heat used1187 GDD available
Hover or tap the dots to see which recommended varieties use that much local heat.
For Yellowknife, 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 needed1187 available before frost
May 24September 21
Tight fit
Why this fit?
Local season fit:
Walla Walla leaves about 87 GDD cushion against the normal Yellowknife 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 Yellowknife because they either run past the normal season or leave too little margin before frost.
ailsa craigLate
Needs1400 GDD
Yellowknife gives1187 GDD
Gap
213 GDD short
1187 GDD available before frost213 more GDD needed
May 24September 21
Runs past season
Why not a main pick?
Local season fit:
ailsa craig usually needs about 213 more GDD than Yellowknife 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
Yellowknife gives1187 GDD
Gap
113 GDD short
1187 GDD available before frost113 more GDD needed
May 24September 21
Runs past season
Why not a main pick?
Local season fit:
patterson usually needs about 113 more GDD than Yellowknife 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
Yellowknife gives1187 GDD
Gap
113 GDD short
1187 GDD available before frost113 more GDD needed
May 24September 21
Runs past season
Why not a main pick?
Local season fit:
redwing usually needs about 113 more GDD than Yellowknife 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
Yellowknife gives1187 GDD
Gap
13 GDD short
1187 GDD available before frost13 more GDD needed
May 24September 21
Runs past season
Why not a main pick?
Local season fit:
copra usually needs about 13 more GDD than Yellowknife 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
Workable
Early
95–105
1200
Tight
Mid-season
105–115
1300
Poor fit
Late
115–120
1400
Poor fit
Main risk: There is not much margin here, so late planting or longer-season onion varieties can easily carry harvest past frost.
How Frost Affects Planting Dates for Onions in Yellowknife
Yellowknife usually has about 120 frost-free days, with a typical last spring frost around May 24 and a typical first fall frost around September 21.
Typical last spring frostMay 24
Typical first fall frostSeptember 21
Typical frost-free days120
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 Yellowknife, the seasonal margin for onions is tighter before the usual fall frost around September 21, so microclimate matters more than it does for easier crops. Local gardens do not all warm and cool at the same pace. For a better local margin, gardeners usually do best in south-facing walls, sheltered gardens, raised beds, and sunnier urban lots. Cooler spots like low spots, exposed sites, and shadier yards often make timing tighter. For onions, the best local sites often help the crop get moving earlier and 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.
