When to plant · 14 cities · zones 6b–7a
When to plant onions in Connecticut
Start Spanish Onion seeds indoors around Jan 26 and transplant around Mar 23 — the Connecticut statewide median, counted from a last spring frost of Apr 20 across 289 ZIP codes and 29 NOAA stations.
The rule: Twelve weeks indoors, the earliest sowing on the calendar, then transplant about four weeks before the last frost.
Connecticut onions, by step
Statewide median last frost Apr 20, first fall frost Oct 20, 2027 season. Each cultivar's own indoor lead time and days to maturity, same engine as the Plan Builder.
| Cultivar | Start indoors | Plant out | First harvest | Days |
|---|---|---|---|---|
| Spanish OnionYellow Sweet Spanish (long-day) | Jan 26 | Mar 23 | Jul 11 | 110 from transplant |
Tight means first harvest lands within two weeks of the median first fall frost. Statewide dates are the ZIP-weighted median of every NOAA 1991–2020 station Connecticut's ZIP codes resolve to.
Onions in Connecticut, city by city
Spanish Onion, scheduled from each city's nearest NOAA station — the same dates as its frost page.
| City | Last frost | Start indoors | Plant out | First harvest |
|---|---|---|---|---|
| Bridgeportzone 7a | Apr 5 | Jan 11 | Mar 8 | Jun 26 |
| Stamfordzone 7a | Apr 17 | Jan 23 | Mar 20 | Jul 8 |
| New Havenzone 7a | Apr 17 | Jan 23 | Mar 20 | Jul 8 |
| Hartfordzone 6b | Apr 17 | Jan 23 | Mar 20 | Jul 8 |
| Waterburyzone 6b | Apr 26 | Feb 1 | Mar 29 | Jul 17 |
| Norwalkzone 7a | Apr 17 | Jan 23 | Mar 20 | Jul 8 |
| Danburyzone 6b | Apr 20 | Jan 26 | Mar 23 | Jul 11 |
| New Britainzone 6b | Apr 17 | Jan 23 | Mar 20 | Jul 8 |
| Bristolzone 6b | Apr 25 | Jan 31 | Mar 28 | Jul 16 |
| Meridenzone 6b | Apr 26 | Feb 1 | Mar 29 | Jul 17 |
| West Havenzone 7a | Apr 17 | Jan 23 | Mar 20 | Jul 8 |
| Milfordzone 7a | Apr 5 | Jan 11 | Mar 8 | Jun 26 |
| Middletownzone 6b | Apr 26 | Feb 1 | Mar 29 | Jul 17 |
| Sheltonzone 6b | Apr 5 | Jan 11 | Mar 8 | Jun 26 |
What these onions become
What Connecticut onions need
Yellow Sweet Spanish Onion Seed
A long-day storage onion with enough sugar to sweat down without scorching. The aromatic base under every tomato sauce on this site.
Organic Seed Starter Potting MixMust have
Seed-starting mix is not potting soil with a nicer label — it is finer, lighter, and low in nutrients on purpose, because a seedling's first roots want air and moisture, not fertiliser.
72-Cell Trays with 1020 Bottoms, 5-PackMust have
The cheap black nursery trays crack after one season and flex enough to break roots when you lift them. These do not. Over five seasons the price per use is lower than the throwaways.
T8 Full-Spectrum Grow Lights, 1 ft 4-packMust have
A south window in March delivers a fraction of the light a pepper seedling needs, and the plant tells you by stretching. Two inches of LED above the canopy for 16 hours a day fixes it permanently.
Rapitest Soil Test Kit
In-ground growers are guessing until they test. pH outside 6.0–6.8 locks nutrients out no matter how much fertiliser you add, and no amount of feeding fixes that.
Pure Organic Worm Castings, 15 lb
Not a fertiliser so much as a soil-biology inoculant with a mild nutrient charge. A cup in each planting hole is a cheap, unglamorous improvement you can measure by August.
Garden Harvest Basket with Tool Caddy
A harvest basket that doubles as a colander means the hose rinse happens in the garden, and the dirt stays outside. On a 20-pound tomato day that is a genuine time saving.
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Onions in Connecticut: questions
When should I plant onions in Connecticut?
Transplant around Mar 23 at the statewide median; across the state that date runs from Mar 17 in the warmest tenth of Connecticut's ZIP codes to Apr 5 in the coldest. To cut the freeze risk to one year in ten, count from May 6 instead of the median last frost. Use the city table for your own town.
When do I start onions seeds indoors in Connecticut?
Around Jan 26 for Spanish Onion: 12 weeks before the statewide median last frost, on soil held at 65–75 °F.
When is the last frost in Connecticut?
The ZIP-weighted median of NOAA 1991–2020 station medians is Apr 20. In the warmest tenth of Connecticut's ZIP codes the median last frost falls on or before Apr 14; in the coldest tenth, on or after May 3.
When will Connecticut onions be ready to harvest?
Spanish Onion planted on the statewide date is ready around Jul 11: 110 days from transplant.
Which onions grow in Connecticut?
Spanish Onion is a long-day onion, correct above roughly 36° N. Every Connecticut city listed here is north of that line.
More for Connecticut
- When to plant tomatoes
- When to plant peppers
- When to plant tomatillos
- When to plant basil
- When to plant cilantro
- When to plant carrots
- When to plant mustard greens
Onions in every state → · Connecticut frost dates → · How frost-date math works →