When to plant onions in New Mexico
New Mexico’s average last spring frost is April 20, and the first fall frost typically arrives around October 20 — about 183 frost-free days (USDA zones 4b, 5b, 6b, 7a, 7b, 8a, 9a). Onion needs 90–120 days to mature, which fits comfortably within New Mexico's growing season.
New Mexico covers a wide range of climates, so your exact frost dates may differ from the state average by two weeks or more. For dates tuned to your town, use the calendar generator.
When to plant onions in New Mexico: the short answer
For a spring planting, plant out Mar 23 – Apr 9, with seeds started indoors Feb 2 – Feb 16. Seeds germinate in soil from 40 to 90°F.
Windows are ~1–2 week bands around each date. Frost dates are a statewide average from NOAA/NCEI normals; your town may differ by two weeks or more. Calendar year 2026.
How to grow onions in New Mexico, step by step
- Start seeds indoors (Feb 2 – Feb 16). Sow seeds ½ inch deep in seed-starting mix under bright light. They take 7-14 days to sprout, fastest in soil around 70°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. They need at least six to eight hours of direct sun a day and loose soil at least 12 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (Mar 23 – Apr 9). Space plants about 4 inches apart in rows 12 inches apart. It handles frost well, so it can go out before the last frost date. As a cool-season crop it does best before summer heat arrives in New Mexico.
- Water and feed. Give it steady, even moisture, about an inch of water a week from rain or the hose.
- Watch for pests and problems. Pests: onion maggot, onion thrips. Diseases and disorders: downy mildew, white rot, neck rot, purple blotch.
- Harvest (from about Jun 28 – Jul 28). Onion takes 90-120 days to reach harvest. Match the day-length type to your latitude: long-day onions for the north, short-day for the south, day-neutral anywhere. Bulbing is triggered by day length, not calendar date.
Figures come from our crop data; dates use New Mexico’s average frost dates. More in the full onion growing guide.
Onion planting dates by USDA zone in New Mexico
New Mexico spans USDA zones 4b, 5b, 6b, 7a, 7b, 8a, 9a. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average, so the onion dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant onion |
|---|---|---|---|---|---|
| Zone 4 | May 10 | Sep 25 | 135 days | Feb 22 – Mar 8 | Apr 12 – Apr 29 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | Feb 12 – Feb 26 | Apr 2 – Apr 19 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | Jan 28 – Feb 11 | Mar 18 – Apr 4 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | Jan 18 – Feb 1 | Mar 8 – Mar 25 |
| Zone 8 | Mar 20 | Nov 5 | 230 days | Jan 2 – Jan 16 | Feb 20 – Mar 9 |
| Zone 9 | Feb 20 | Nov 30 | 280 days | Dec 5 – Dec 19 | Jan 23 – Feb 9 |
When to plant onions in nearby states
| State | Last frost | Plant out |
|---|---|---|
| New Mexico (this page) | April 20 | Mar 23 – Apr 9 |
| Arizona | March 15 | Feb 15 – Mar 4 |
Questions gardeners in New Mexico ask
When is the best time to plant onions in New Mexico?
Plant onion transplants outdoors in New Mexico between March 23 and April 9. That timing is set by New Mexico's average last spring frost of April 20; New Mexico spans several climates, so cooler and higher parts of the state run later.
When should I start onion seeds indoors in New Mexico?
Start seeds indoors between February 2 and February 16, about 10 weeks before the last frost, so the seedlings are ready to plant out from March 23.
When will onions planted in New Mexico be ready to harvest?
Planted on time, onions are usually ready from about June 28 to July 28, 90-120 days after transplanting.
When is the last frost in New Mexico?
On average around April 20, with the first fall frost around October 20 - about 183 frost-free days. Your town may differ by two weeks or more.