When to Plant Onions in Alaska
The backbone of the kitchen garden. Choose short-day, intermediate, or long-day varieties based on your latitude.
The Short Answer
Alaska Frost Dates
Your planting dates depend on which part of Alaska you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Interior Alaska | 1a, 2a, 2b | May 15 - Jun 1 | Aug 20 - Sep 10 |
| Southcentral Alaska | 3b, 4a, 4b | May 1 - May 20 | Sep 10 - Sep 25 |
| Southeast Alaska | 5a, 5b, 6a | Apr 15 - May 5 | Sep 25 - Oct 15 |
Onions Planting Schedule for Alaska
Interior Alaska (Zones 1a, 2a, 2b)
Average last frost: May 15 - Jun 1 · Average first frost: Aug 20 - Sep 10
Southcentral Alaska (Zones 3b, 4a, 4b)
Average last frost: May 1 - May 20 · Average first frost: Sep 10 - Sep 25
Southeast Alaska (Zones 5a, 5b, 6a)
Average last frost: Apr 15 - May 5 · Average first frost: Sep 25 - Oct 15
Growing Onions in Alaska
Onions in Alaska's Climate
You're in long-day onion territory — plant varieties that bulb when days exceed 14-16 hours. This means Copra, Walla Walla, and Yellow Globe Danvers. Plant sets or transplants from mid-April. The critical distinction: short-day onions from southern catalogs will NOT form bulbs in your zone because your long summer days trigger bulbing too early, before the plant is large enough.
Soil Considerations for Alaska
Varies widely. Interior has permafrost challenges. Raised beds essential for warming soil. Highly acidic soils common. Loose, well-drained soil is especially important for onions since the edible portion grows underground. If your soil is heavy clay, consider raised beds.
Alaska Climate & Growing Season
Extreme daylight variation. Summer days of 18-24 hours of sunlight accelerate growth. Very short growing season in interior. Onions can handle frost well, which is an advantage in Alaska's climate. You can push planting dates earlier in spring and extend into fall.
Growing season length varies across Alaska: Interior Alaska (1a, 2a, 2b) has a last frost around May 15 - Jun 1, while Southeast Alaska (5a, 5b, 6a) sees frost end around Apr 15 - May 5. This difference matters for onions — but onions handle frost well, so the timing difference is less critical.
Growing Tips
Day length triggers bulbing. Northern gardeners need long-day varieties. Southern gardeners need short-day varieties.
Companion Planting
Plant onions alongside these companions for better growth:
Keep onions away from:
The Bottom Line
Last reviewed: March 29, 2026