When to plant · 5 cities · zones 6b–7a
When to plant onions in Kentucky
Start Spanish Onion seeds indoors around Jan 21 and transplant around Mar 18 — the Kentucky statewide median, counted from a last spring frost of Apr 15 across 742 ZIP codes and 123 NOAA stations.
The rule: Twelve weeks indoors, the earliest sowing on the calendar, then transplant about four weeks before the last frost.
Kentucky onions, by step
Statewide median last frost Apr 15, first fall frost Oct 25, 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 21 | Mar 18 | Jul 6 | 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 Kentucky's ZIP codes resolve to.
Onions in Kentucky, 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 |
|---|---|---|---|---|
| Louisvillezone 7a | Apr 3 | Jan 9 | Mar 6 | Jun 24 |
| Lexingtonzone 7a | Apr 13 | Jan 19 | Mar 16 | Jul 4 |
| Bowling Greenzone 7a | Apr 5 | Jan 11 | Mar 8 | Jun 26 |
| Owensborozone 7a | Apr 2 | Jan 8 | Mar 5 | Jun 23 |
| Covingtonzone 6b | Apr 16 | Jan 22 | Mar 19 | Jul 7 |
What these onions become
What Kentucky 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 Kentucky: questions
When should I plant onions in Kentucky?
Transplant around Mar 18 at the statewide median; across the state that date runs from Mar 6 in the warmest tenth of Kentucky's ZIP codes to Mar 27 in the coldest. To cut the freeze risk to one year in ten, count from May 2 instead of the median last frost. Use the city table for your own town.
When do I start onions seeds indoors in Kentucky?
Around Jan 21 for Spanish Onion: 12 weeks before the statewide median last frost, on soil held at 65–75 °F.
When is the last frost in Kentucky?
The ZIP-weighted median of NOAA 1991–2020 station medians is Apr 15. In the warmest tenth of Kentucky's ZIP codes the median last frost falls on or before Apr 3; in the coldest tenth, on or after Apr 24.
When will Kentucky onions be ready to harvest?
Spanish Onion planted on the statewide date is ready around Jul 6: 110 days from transplant.
Which onions grow in Kentucky?
Spanish Onion is a long-day onion, correct above roughly 36° N. Every Kentucky city listed here is north of that line.
More for Kentucky
- 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 → · Kentucky frost dates → · How frost-date math works →