When to Plant Onions in New Hampshire
The backbone of the kitchen garden. Choose short-day, intermediate, or long-day varieties based on your latitude.
The Short Answer
New Hampshire Frost Dates
Your planting dates depend on which part of New Hampshire you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Northern New Hampshire | 3b, 4a, 4b | May 20 - Jun 5 | Sep 10 - Sep 25 |
| Southern New Hampshire | 5a, 5b, 6a | May 1 - May 20 | Sep 25 - Oct 10 |
Onions Planting Schedule for New Hampshire
Northern New Hampshire (Zones 3b, 4a, 4b)
Average last frost: May 20 - Jun 5 · Average first frost: Sep 10 - Sep 25
Southern New Hampshire (Zones 5a, 5b, 6a)
Average last frost: May 1 - May 20 · Average first frost: Sep 25 - Oct 10
Growing Onions in New Hampshire
Onions in New Hampshire'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 New Hampshire
Rocky, acidic New England soils. Glacial deposits. Granite bedrock. Raised beds essential in many areas. Loose, well-drained soil is especially important for onions since the edible portion grows underground. If your soil is heavy clay, consider raised beds.
New Hampshire Climate & Growing Season
Short growing season especially in north. Cold winters. Cool summers. Hardy varieties important. Onions can handle frost well, which is an advantage in New Hampshire's climate. You can push planting dates earlier in spring and extend into fall.
Growing season length varies across New Hampshire: Northern New Hampshire (3b, 4a, 4b) has a last frost around May 20 - Jun 5, while Southern New Hampshire (5a, 5b, 6a) sees frost end around May 1 - May 20. 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