When to Plant Onions in Connecticut
The backbone of the kitchen garden. Choose short-day, intermediate, or long-day varieties based on your latitude.
The Short Answer
Connecticut Frost Dates
Your planting dates depend on which part of Connecticut you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Northern Connecticut | 5b, 6a | May 1 - May 15 | Sep 25 - Oct 10 |
| Coastal Connecticut | 6b, 7a | Apr 15 - May 1 | Oct 10 - Oct 25 |
Onions Planting Schedule for Connecticut
Northern Connecticut (Zones 5b, 6a)
Average last frost: May 1 - May 15 · Average first frost: Sep 25 - Oct 10
Coastal Connecticut (Zones 6b, 7a)
Average last frost: Apr 15 - May 1 · Average first frost: Oct 10 - Oct 25
Growing Onions in Connecticut
Onions in Connecticut's Climate
Long-day onions are your type. Plant sets or transplants as soon as ground can be worked in spring. For the largest bulbs, start from seed indoors 10-12 weeks before last frost. Your June day length (15+ hours) triggers proper bulbing. Cure in a warm, dry location for 2-3 weeks before storage.
Soil Considerations for Connecticut
Rocky New England soil common. Acidic in many areas. Raised beds popular for dealing with rocky ground. Loose, well-drained soil is especially important for onions since the edible portion grows underground. If your soil is heavy clay, consider raised beds.
Connecticut Climate & Growing Season
Four distinct seasons. Maritime influence moderates coastal temperatures. Shorter growing season inland. Onions can handle frost well, which is an advantage in Connecticut's climate. You can push planting dates earlier in spring and extend into fall.
Growing season length varies across Connecticut: Northern Connecticut (5b, 6a) has a last frost around May 1 - May 15, while Coastal Connecticut (6b, 7a) sees frost end around Apr 15 - May 1. 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