When to Plant Onions in Maine
The backbone of the kitchen garden. Choose short-day, intermediate, or long-day varieties based on your latitude.
The Short Answer
Maine Frost Dates
Your planting dates depend on which part of Maine you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Northern Maine | 3b, 4a, 4b | May 20 - Jun 5 | Sep 10 - Sep 25 |
| Central Maine | 4b, 5a | May 10 - May 25 | Sep 20 - Oct 5 |
| Southern/Coastal Maine | 5a, 5b, 6a | May 1 - May 15 | Sep 25 - Oct 15 |
Onions Planting Schedule for Maine
Northern Maine (Zones 3b, 4a, 4b)
Average last frost: May 20 - Jun 5 · Average first frost: Sep 10 - Sep 25
Central Maine (Zones 4b, 5a)
Average last frost: May 10 - May 25 · Average first frost: Sep 20 - Oct 5
Southern/Coastal Maine (Zones 5a, 5b, 6a)
Average last frost: May 1 - May 15 · Average first frost: Sep 25 - Oct 15
Growing Onions in Maine
Onions in Maine'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 Maine
Acidic, rocky soils. Blueberries thrive naturally. Raised beds common to deal with rocks. Amendment with lime needed for many vegetables. Loose, well-drained soil is especially important for onions since the edible portion grows underground. If your soil is heavy clay, consider raised beds.
Maine Climate & Growing Season
Short growing season but long summer days help. Maritime influence on coast. Season extension techniques very valuable. Onions can handle frost well, which is an advantage in Maine's climate. You can push planting dates earlier in spring and extend into fall.
Growing season length varies across Maine: Northern Maine (3b, 4a, 4b) has a last frost around May 20 - Jun 5, while Southern/Coastal Maine (5a, 5b, 6a) sees frost end around May 1 - May 15. 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