When to plant · 24 cities · zones 4a–5a
When to plant onions in Minnesota
Start Spanish Onion seeds indoors around Feb 9 and transplant around Apr 6 — the Minnesota statewide median, counted from a last spring frost of May 4 across 874 ZIP codes and 186 NOAA stations.
The rule: Twelve weeks indoors, the earliest sowing on the calendar, then transplant about four weeks before the last frost.
Minnesota onions, by step
Statewide median last frost May 4, first fall frost Oct 4, 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) | Feb 9 | Apr 6 | Jul 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 Minnesota's ZIP codes resolve to; 7 of 881 ZIPs have no datable freeze and are left out.
Onions in Minnesota, 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 |
|---|---|---|---|---|
| Minneapoliszone 5a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| St. Paulzone 5a | Apr 24 | Jan 30 | Mar 27 | Jul 15 |
| Rochesterzone 4b | Apr 30 | Feb 5 | Apr 2 | Jul 21 |
| Bloomingtonzone 5a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| Duluthzone 4b | May 14 | Feb 19 | Apr 16 | Aug 4 |
| Brooklyn Parkzone 5a | Apr 30 | Feb 5 | Apr 2 | Jul 21 |
| Woodburyzone 5a | Apr 26 | Feb 1 | Mar 29 | Jul 17 |
| Plymouthzone 5a | Apr 29 | Feb 4 | Apr 1 | Jul 20 |
| Lakevillezone 4b | Apr 27 | Feb 2 | Mar 30 | Jul 18 |
| Blainezone 5a | May 5 | Feb 10 | Apr 7 | Jul 26 |
| Maple Grovezone 5a | Apr 30 | Feb 5 | Apr 2 | Jul 21 |
| St. Cloudzone 4b | May 3 | Feb 8 | Apr 5 | Jul 24 |
| Eaganzone 5a | May 2 | Feb 7 | Apr 4 | Jul 23 |
| Burnsvillezone 5a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| Coon Rapidszone 5a | May 5 | Feb 10 | Apr 7 | Jul 26 |
| Eden Prairiezone 5a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| Apple Valleyzone 5a | May 2 | Feb 7 | Apr 4 | Jul 23 |
| Edinazone 5a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| Minnetonkazone 5a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| St. Louis Parkzone 5a | Apr 29 | Feb 4 | Apr 1 | Jul 20 |
| Shakopeezone 5a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| Mankatozone 5a | Apr 30 | Feb 5 | Apr 2 | Jul 21 |
| Moorheadzone 4a | May 5 | Feb 10 | Apr 7 | Jul 26 |
| Cottage Grovezone 5a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
What these onions become
What Minnesota 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 Minnesota: questions
When should I plant onions in Minnesota?
Transplant around Apr 6 at the statewide median; across the state that date runs from Mar 28 in the warmest tenth of Minnesota's ZIP codes to Apr 18 in the coldest. To cut the freeze risk to one year in ten, count from May 18 instead of the median last frost. Use the city table for your own town.
When do I start onions seeds indoors in Minnesota?
Around Feb 9 for Spanish Onion: 12 weeks before the statewide median last frost, on soil held at 65–75 °F.
When is the last frost in Minnesota?
The ZIP-weighted median of NOAA 1991–2020 station medians is May 4. In the warmest tenth of Minnesota's ZIP codes the median last frost falls on or before Apr 25; in the coldest tenth, on or after May 16.
When will Minnesota onions be ready to harvest?
Spanish Onion planted on the statewide date is ready around Jul 25: 110 days from transplant.
Which onions grow in Minnesota?
Spanish Onion is a long-day onion, correct above roughly 36° N. Every Minnesota city listed here is north of that line.
More for Minnesota
- 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 → · Minnesota frost dates → · How frost-date math works →