Climate-based onion planting guide for Anchorage, Alaska
When to Plant Onions in Anchorage: Timing and Maturity Guide
Onions are generally a good local option in Anchorage, especially when gardeners stay close to planting windows and choose varieties that match local conditions.
Typical Planting Window
Use the planting dates below for onions in Anchorage.
Gardeners usually start indoors around February 13 and plant outdoors from about April 10. Most varieties need about 95–110 days to reach maturity once they are in the garden.
Onions are usually workable in Anchorage with normal timing and reasonable variety choice. This is a good fit, but it still rewards gardeners who stay close to the local season.
The season can support onions, though it is not so generous that growers can ignore timing.
Best local strategy: Use dependable varieties and focus on a timely start, steady growth, and good spacing.
Can Onions Mature in Anchorage?
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, Anchorage typically provides about 1396 growing degree days for onions. With a typical crop target of 1300, that leaves a heat margin of +96. That heat margin usually gives the crop enough room to finish, but not so much that delays stop mattering. Timing and variety choice still affect how comfortably the crop fits.
GDD Checkpoints for Anchorage
If planting later than usual, this table shows how much growing degree day heat is still available from each point in the season. It is most useful for judging how much flexibility you still have before the crop starts losing margin.
| Checkpoint | Remaining GDD | Heat margin | Fit vs typical target |
|---|---|---|---|
| Apr 15 | 1396 | +96 | Usually fits |
| May 15 | 1376 | +76 | Usually fits |
| Jun 1 | 1285 | -15 | Usually short |
| Jun 15 | 1154 | -146 | Usually short |
| Jul 1 | 953 | -347 | Usually short |
Best Onion Varieties for Anchorage
In Anchorage, very early to mid-season onion varieties are usually the best fit in a typical year. Slower choices can still work when gardeners want their specific qualities and do not give away margin through delay.
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
- Redwing — a strong red storage type where the season is reasonably supportive
- Patterson — a solid keeping onion that wants enough runway to size up well
| Variety class | Typical days to maturity | Typical GDD need | Local fit |
|---|---|---|---|
| Very early | 90–95 | 1100 | Good fit |
| Early | 95–105 | 1200 | Workable |
| Mid-season | 105–115 | 1300 | Workable |
| Late | 115–120 | 1400 | Tight |
Main risk: The usual risk here is losing time early, since delayed planting or cool starts can slow maturity for longer-season onion varieties.
How Frost Affects Onions in Anchorage
Anchorage usually has about 151 frost-free days, with a typical last spring frost around May 1 and a typical first fall frost around September 29.
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 usual trouble comes from delayed planting or from choosing slower varieties when the local season would reward simpler, faster choices.
In Anchorage, onions usually have enough season to work well, but site warmth still affects how comfortably they finish before the usual fall frost around September 29. 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.
Related crops
Related crops worth comparing for the same city:
For a broader local overview, see the Anchorage planting guide. You can also use the Growing Degree Day Planner to test planting dates and crop timing.