When to plant · 7 cities · zones 6b–8b
When to plant onions in New Mexico
Start Spanish Onion seeds indoors around Feb 7 and transplant around Apr 4 — the New Mexico statewide median, counted from a last spring frost of May 2 across 371 ZIP codes and 156 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 New Mexico 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.
New Mexico onions, by step
Statewide median last frost May 2, first fall frost Oct 15, 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 7 | Apr 4 | Jul 23 | 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 New Mexico's ZIP codes resolve to.
Onions in New Mexico, 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 |
|---|---|---|---|---|
| Albuquerquezone 7bbelow 36° N · short-day onion | Apr 6 | Jan 12 | Mar 9 | Jun 27 |
| Las Cruceszone 8bbelow 36° N · short-day onion | Mar 12 | Dec 18 | Feb 12 | Jun 2 |
| Rio Ranchozone 7bbelow 36° N · short-day onion | Apr 16 | Jan 22 | Mar 19 | Jul 7 |
| Santa Fezone 6bbelow 36° N · short-day onion | May 2 | Feb 7 | Apr 4 | Jul 23 |
| Roswellzone 7bbelow 36° N · short-day onion | Mar 29 | Jan 4 | Mar 1 | Jun 19 |
| Farmingtonzone 7a | May 2 | Feb 7 | Apr 4 | Jul 23 |
| Hobbszone 8abelow 36° N · short-day onion | Mar 28 | Jan 3 | Feb 28 | Jun 18 |
What these onions become
What New Mexico 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 New Mexico: questions
When should I plant onions in New Mexico?
Transplant around Apr 4 at the statewide median; across the state that date runs from Mar 1 in the warmest tenth of New Mexico's ZIP codes to May 1 in the coldest. To cut the freeze risk to one year in ten, count from May 17 instead of the median last frost. Use the city table for your own town.
When do I start onions seeds indoors in New Mexico?
Around Feb 7 for Spanish Onion: 12 weeks before the statewide median last frost, on soil held at 65–75 °F.
When is the last frost in New Mexico?
The ZIP-weighted median of NOAA 1991–2020 station medians is May 2. In the warmest tenth of New Mexico's ZIP codes the median last frost falls on or before Mar 29; in the coldest tenth, on or after May 29.
When will New Mexico onions be ready to harvest?
Spanish Onion planted on the statewide date is ready around Jul 23: 110 days from transplant.
Which onions grow in New Mexico?
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 7 New Mexico cities listed here sit below that line; grow a short-day onion there.
More for New Mexico
- 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 → · New Mexico frost dates → · How frost-date math works →