Practical planning tools for short growing seasons.
Climate-based onion planting guide for Durango, Colorado
When to Plant Onions in Durango
Onions are often difficult in Durango because the local season is short enough that the crop can easily run out of time or heat before finishing well.
Typical Planting Window
Risky in this climate
Use the planting dates below for onions in Durango.
Start indoors
March 12
Typical planting windowMay 7 – May 21
MethodTransplant
Typical days to maturity95–110
Onions are usually started indoors around March 12 and planted outdoors during the normal local window of May 7 to May 21.
Most varieties need about 95–110 days to reach maturity once they are in the garden.
Onions are usually a higher-risk crop in Durango. Success tends to come from careful variety choice and the most favorable microclimates available.
Durango usually gets into the planting season for onions slightly later than many other Colorado locations.
Best local strategy:
Use the earliest practical starts, the fastest varieties, and the warmest protected sites available.
Can Onions Mature in Durango?
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)903
Typical crop GDD target1300
Heat margin-397
From the usual planting window, Durango typically provides about 903 growing degree days for onions. With a typical crop target of 1300, that leaves a heat margin of -397. That heat shortfall means the crop usually needs the fastest approach and the warmest local conditions to have a realistic chance of finishing well.
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
903
-397
Usually short
Jun 1
899
-401
Usually short
Jun 15
852
-448
Usually short
Jul 1
734
-566
Usually short
How Different Onion Varieties Affect Results
In Durango, only the fastest onion varieties are realistic candidates in a typical year. Larger and later types usually run out of season before finishing well.
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 Durango
Onion variety choice matters in Durango, especially when slower maturity ranges start spending too much local margin. The local season can support onions, so the main choice is usually about bulb size, sweetness, color, and keeping quality.
May 28
local season starts
September 30
frost pressure returns
Less heat used903 GDD available
Hover or tap the dots to see which recommended varieties use that much local heat.
For Durango, Walla Walla
is
the most realistic onion
option
for this short-season fit.
It needs
good timing, steady early growth, and realistic expectations.
Compare each variety’s heat need and maturity timing against the local frost-free window before choosing what to grow.
Closest matches for a marginal season
Walla WallaVery early
1100 GDD needed903 available before frost
May 28September 30
Usually too long
Why this fit?
Local season fit:
Walla Walla is about 197 GDD short against the normal Durango 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 Durango because they either run past the normal season or leave too little margin before frost.
ailsa craigLate
Needs1400 GDD
Durango gives903 GDD
Gap
497 GDD short
903 GDD available before frost497 more GDD needed
May 28September 30
Runs past season
Why not a main pick?
Local season fit:
ailsa craig usually needs about 497 more GDD than Durango 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
Durango gives903 GDD
Gap
397 GDD short
903 GDD available before frost397 more GDD needed
May 28September 30
Runs past season
Why not a main pick?
Local season fit:
patterson usually needs about 397 more GDD than Durango 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
Durango gives903 GDD
Gap
397 GDD short
903 GDD available before frost397 more GDD needed
May 28September 30
Runs past season
Why not a main pick?
Local season fit:
redwing usually needs about 397 more GDD than Durango 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
Durango gives903 GDD
Gap
297 GDD short
903 GDD available before frost297 more GDD needed
May 28September 30
Runs past season
Why not a main pick?
Local season fit:
copra usually needs about 297 more GDD than Durango 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
Poor fit
Early
95–105
1200
Poor fit
Mid-season
105–115
1300
Poor fit
Late
115–120
1400
Poor fit
Main risk: In this location, the season is often too short for the crop to finish well before conditions turn against it.
How Frost Affects Planting Dates for Onions in Durango
Durango usually has about 125 frost-free days, with a typical last spring frost around May 28 and a typical first fall frost around September 30.
Typical last spring frostMay 28
Typical first fall frostSeptember 30
Typical frost-free days125
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 crop usually falls short here because the season runs out before it finishes well. Late planting, cool nights, and slower varieties make that problem much worse.
In Durango, the seasonal margin for onions is tighter before the usual fall frost around September 30, 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.
