Climate-based onion planting guide for Jackson, Wyoming
When to Plant Onions in Jackson: Timing and Maturity Guide
In Jackson, onions can work, but the local season leaves limited room for delay or slower choices.
Typical Planting Window
Use the planting dates below for onions in Jackson.
Gardeners usually start indoors around April 4 and plant outdoors from about May 30. Most varieties need about 95–110 days to reach maturity once they are in the garden.
Gardeners can still grow onions in Jackson, but success usually depends on treating earliness and warm placement as part of the plan rather than as nice bonuses.
Within Wyoming, Jackson usually reaches onion planting time a little later than many comparable locations. That makes local site warmth more important than it would be where the seasonal margin is wider.
Best local strategy: Use the earliest practical timing, favor quicker varieties, and avoid cooler exposed sites.
Can Onions Mature in Jackson?
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.
From the usual planting window, Jackson typically provides about 1237 growing degree days for onions. With a typical crop target of 1300, that leaves a heat margin of -63. That narrow heat margin means small delays or slower varieties can quickly reduce the odds of timely maturity.
GDD Checkpoints for Jackson
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 | 1530 | +230 | Comfortable |
| May 15 | 1521 | +221 | Comfortable |
| Jun 1 | 1442 | +142 | Usually fits |
| Jun 15 | 1329 | +29 | Tight fit |
| Jul 1 | 1147 | -153 | Usually short |
Best Onion Varieties for Jackson
In Jackson, very early onion varieties are usually the most dependable choices, while early and mid-season 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
- Copra — a dependable storage onion with good all-around practicality
| 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 | Tight |
| Late | 115–120 | 1400 | Poor fit |
Main risk: Delays in planting or slower onion varieties can quickly push maturity past fall frost.
How Frost Affects Onions in Jackson
Jackson usually has about 72 frost-free days, with a typical last spring frost around June 20 and a typical first fall frost around August 31.
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.
Onions are closer to the limits of the local season in Jackson before fall frost around August 31, so microclimate plays a bigger role here than it does for easier crops. Local gardens do not all warm and cool at the same pace. In practical terms, the best spots are usually south-facing walls, sheltered gardens, raised beds, and sunnier urban lots. Cooler spots like low spots, exposed sites, and shadier yards are more likely to stay cooler and be less forgiving. For onions, warmer local sites usually help the crop get established earlier and grow a little more steadily.
Related crops
Related crops worth comparing for the same city:
For a broader local overview, see the Jackson planting guide. You can also use the Growing Degree Day Planner to test planting dates and crop timing.