When to plant · 11 cities · zones 7a–7b
When to plant onions in Oklahoma
Start Spanish Onion seeds indoors around Jan 10 and transplant around Mar 7 — the Oklahoma statewide median, counted from a last spring frost of Apr 4 across 665 ZIP codes and 192 NOAA stations.
The rule: Twelve weeks indoors, the earliest sowing on the calendar, then transplant about four weeks before the last frost.
6 of these Oklahoma cities sit below 36° N, where a long-day onion never gets the day length to bulb. They are flagged in the table; plant a short-day type there.
Oklahoma onions, by step
Statewide median last frost Apr 4, first fall frost Nov 2, 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 10 | Mar 7 | Jun 25 | 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 Oklahoma's ZIP codes resolve to.
Onions in Oklahoma, 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 |
|---|---|---|---|---|
| Oklahoma Cityzone 7bbelow 36° N · short-day onion | Apr 4 | Jan 10 | Mar 7 | Jun 25 |
| Tulsazone 7b | Mar 31 | Jan 6 | Mar 3 | Jun 21 |
| Normanzone 7bbelow 36° N · short-day onion | Mar 31 | Jan 6 | Mar 3 | Jun 21 |
| Broken Arrowzone 7b | Apr 1 | Jan 7 | Mar 4 | Jun 22 |
| Edmondzone 7bbelow 36° N · short-day onion | Apr 10 | Jan 16 | Mar 13 | Jul 1 |
| Lawtonzone 7bbelow 36° N · short-day onion | Mar 26 | Jan 1 | Feb 26 | Jun 16 |
| Moorezone 7bbelow 36° N · short-day onion | Mar 31 | Jan 6 | Mar 3 | Jun 21 |
| Midwest Cityzone 7bbelow 36° N · short-day onion | Apr 2 | Jan 8 | Mar 5 | Jun 23 |
| Enidzone 7a | Apr 6 | Jan 12 | Mar 9 | Jun 27 |
| Stillwaterzone 7a | Apr 5 | Jan 11 | Mar 8 | Jun 26 |
| Owassozone 7b | Mar 31 | Jan 6 | Mar 3 | Jun 21 |
What these onions become
What Oklahoma 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 Oklahoma: questions
When should I plant onions in Oklahoma?
Transplant around Mar 7 at the statewide median; across the state that date runs from Feb 28 in the warmest tenth of Oklahoma's ZIP codes to Mar 15 in the coldest. To cut the freeze risk to one year in ten, count from Apr 20 instead of the median last frost. Use the city table for your own town.
When do I start onions seeds indoors in Oklahoma?
Around Jan 10 for Spanish Onion: 12 weeks before the statewide median last frost, on soil held at 65–75 °F.
When is the last frost in Oklahoma?
The ZIP-weighted median of NOAA 1991–2020 station medians is Apr 4. In the warmest tenth of Oklahoma's ZIP codes the median last frost falls on or before Mar 28; in the coldest tenth, on or after Apr 12.
When will Oklahoma onions be ready to harvest?
Spanish Onion planted on the statewide date is ready around Jun 25: 110 days from transplant.
Which onions grow in Oklahoma?
Spanish Onion is a long-day onion: it bulbs at 14–16 hours of daylight, which it gets above roughly 36° N. 6 of the 11 Oklahoma cities listed here sit below that line; grow a short-day onion there.
More for Oklahoma
- 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 → · Oklahoma frost dates → · How frost-date math works →