When to plant · 16 cities · zones 6a–7a
When to plant onions in Missouri
Start Spanish Onion seeds indoors around Jan 17 and transplant around Mar 14 — the Missouri statewide median, counted from a last spring frost of Apr 11 across 1,047 ZIP codes and 193 NOAA stations.
The rule: Twelve weeks indoors, the earliest sowing on the calendar, then transplant about four weeks before the last frost.
Missouri onions, by step
Statewide median last frost Apr 11, 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 17 | Mar 14 | Jul 2 | 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 Missouri's ZIP codes resolve to.
Onions in Missouri, 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 |
|---|---|---|---|---|
| Kansas Cityzone 6b | Apr 4 | Jan 10 | Mar 7 | Jun 25 |
| St. Louiszone 7a | Apr 1 | Jan 7 | Mar 4 | Jun 22 |
| Springfieldzone 7a | Apr 9 | Jan 15 | Mar 12 | Jun 30 |
| Columbiazone 6b | Apr 5 | Jan 11 | Mar 8 | Jun 26 |
| Independencezone 6b | Apr 10 | Jan 16 | Mar 13 | Jul 1 |
| Lee's Summitzone 6b | Apr 7 | Jan 13 | Mar 10 | Jun 28 |
| O'Fallonzone 6b | Apr 10 | Jan 16 | Mar 13 | Jul 1 |
| St. Charleszone 6b | Apr 8 | Jan 14 | Mar 11 | Jun 29 |
| St. Josephzone 6a | Apr 19 | Jan 25 | Mar 22 | Jul 10 |
| St. Peterszone 6b | Apr 9 | Jan 15 | Mar 12 | Jun 30 |
| Blue Springszone 6b | Apr 7 | Jan 13 | Mar 10 | Jun 28 |
| Joplinzone 7a | Apr 9 | Jan 15 | Mar 12 | Jun 30 |
| Florissantzone 7a | Apr 2 | Jan 8 | Mar 5 | Jun 23 |
| Chesterfieldzone 7a | Apr 4 | Jan 10 | Mar 7 | Jun 25 |
| Wentzvillezone 6b | Apr 10 | Jan 16 | Mar 13 | Jul 1 |
| Jefferson Cityzone 6b | Apr 10 | Jan 16 | Mar 13 | Jul 1 |
What these onions become
What Missouri 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 Missouri: questions
When should I plant onions in Missouri?
Transplant around Mar 14 at the statewide median; across the state that date runs from Mar 5 in the warmest tenth of Missouri's ZIP codes to Mar 22 in the coldest. To cut the freeze risk to one year in ten, count from Apr 28 instead of the median last frost. Use the city table for your own town.
When do I start onions seeds indoors in Missouri?
Around Jan 17 for Spanish Onion: 12 weeks before the statewide median last frost, on soil held at 65–75 °F.
When is the last frost in Missouri?
The ZIP-weighted median of NOAA 1991–2020 station medians is Apr 11. In the warmest tenth of Missouri's ZIP codes the median last frost falls on or before Apr 2; in the coldest tenth, on or after Apr 19.
When will Missouri onions be ready to harvest?
Spanish Onion planted on the statewide date is ready around Jul 2: 110 days from transplant.
Which onions grow in Missouri?
Spanish Onion is a long-day onion, correct above roughly 36° N. Every Missouri city listed here is north of that line.
More for Missouri
- 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 → · Missouri frost dates → · How frost-date math works →