What does USDA hardiness zone 5a mean in New Mexico?

Zone 5a means an average annual extreme minimum winter temperature of −20 to −15 °F — the standard USDA measure of which perennials survive winter. 1 location in New Mexico fall in this zone. It does not set planting dates; see the frost calendar below for that.

When should I plant tomatoes in New Mexico's zone 5a?

Using Costilla's frost dates (this page's median-season location): start seeds indoors about Apr 5 – Apr 19, then transplant outside about Jun 7 – Jun 14. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.

Does every location in New Mexico's zone 5a have the same frost dates?

No — they do not all share a weather station, so frost dates vary by a week or more across the 1 locations listed (see the table above for each location's own dates).

USDA zone 5a in New Mexico

−20 to −15 °F avg. annual extreme minimum · 1 location in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 5a covers 1 location across New Mexico (average annual extreme minimum −20 to −15 °F): Costilla, NM. Average last spring frost across this group ranges May 31 and growing seasons run 116 days — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every New Mexico location's own frost dates; the printable planting calendar uses Costilla, this group's median-season location.

USDA zone: 5a−20 to −15 °F
Last frost range: May 31avg, 32°F
First frost range: Sep 26avg, 32°F
Growing season range: 116days

Locations in this group

Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.

Own frost dates per location.
Location	Also covers	Nearest station	Last frost	First frost	Season (days)
Costilla *	—	Cerro	May 31	Sep 26	116

* Costilla is this group's median-season location — the calendar below is computed from its data.

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.

Planting calendar (Costilla, representative)

Computed from Costilla's average frost dates — the median-season location in this New Mexicozone 5a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Costilla (New Mexico, zone 5a), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Apr 5 – Apr 19	Jun 7 – Jun 14	Aug 6 – Aug 26	—	matures comfortably
Pepper	Very tender	Mar 22 – Apr 5	Jun 14 – Jun 21	Aug 13 – Sep 12	—	matures comfortably
Cucumber	Tender	May 3 – May 10	Jun 7 – Jun 14	Jul 27 – Aug 16	—	matures comfortably
Summer squash / zucchini	Tender	—	Jun 7 – Jun 14	Jul 22 – Aug 6	—	matures comfortably
Bush bean	Tender	—	Jun 7 – Jun 14	Jul 27 – Aug 6	Jul 28 – Aug 7	matures comfortably
Sweet corn	Tender	—	May 31 – Jun 14	Jul 30 – Aug 29	—	matures comfortably
Basil	Very tender	Apr 19 – May 3	Jun 7 – Jun 14	Jul 7 – Jul 22	—	matures comfortably
Lettuce	Half-hardy	Apr 19 – May 3	May 3 – May 17	Jun 17 – Jul 2	Jul 14 – Jul 29	matures comfortably
Pea	Hardy	—	Apr 19 – May 3	Jun 13 – Jun 28	Jul 4 – Jul 19	matures comfortably
Spinach	Hardy	—	Apr 19 – May 3	May 29 – Jun 8	Jul 24 – Aug 3	matures comfortably
Carrot	Half-hardy	—	May 10 – May 17	Jul 9 – Jul 29	Jun 24 – Jul 14	matures comfortably
Broccoli	Half-hardy	Apr 5 – Apr 19	May 3 – May 17	Jun 27 – Jul 17	Jun 29 – Jul 19	matures comfortably

Which crops fit this growing season

Using Costilla's own 116-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.

Frost & freeze dates (Costilla)

From NOAA's 1991–2020 Climate Normals at station USC00291630. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020), Costilla.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	Jun 11	Jun 28	Sep 17	Sep 27	96
32°F (freeze)	May 31	Jun 13	Sep 26	Oct 6	116
28°F	May 18	Jun 3	Oct 3	Oct 14	138
24°F	May 5	May 19	Oct 10	Oct 23	159

Growing degree days

Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 1 locations is 1,747; Costilla's own reading is shown below.

Annual growing degree days for Costilla (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	1,747	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	3,657	cool-season crops (brassicas, greens)

Hardiness zone 5a in New Mexico

Zone 5a means an average annual extreme minimum winter temperature of about −20 to −15 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. New Mexico spans 8 hardiness zones in this dataset — see all New Mexico locations for the full range, including zones5b, 6a, 6b, 7a, 7b, 8a, 8b.

Explore zone 5a in other states at zone 5a, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 5a mean in New Mexico?: Zone 5a means an average annual extreme minimum winter temperature of −20 to −15 °F — the standard USDA measure of which perennials survive winter. 1 location in New Mexico fall in this zone. It does not set planting dates; see the frost calendar below for that.
When should I plant tomatoes in New Mexico's zone 5a?: Using Costilla's frost dates (this page's median-season location): start seeds indoors about Apr 5 – Apr 19, then transplant outside about Jun 7 – Jun 14. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
Does every location in New Mexico's zone 5a have the same frost dates?: No — they do not all share a weather station, so frost dates vary by a week or more across the 1 locations listed (see the table above for each location's own dates).

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.