Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 81120 — Antonito, CO

ZIP code 81120 (Antonito, Conejos County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 28 and the first fall frost September 21.

Where ZIP 81120 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone5b−15 to −10 °F

Coldest night−26.1 to −23.3 °C

Last frostMay 28

First frostSep 21

2012 zone5a

Was 5a on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Antonito, CO…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Antonito, CO

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMay 28median — 50% chance of a later frost

Safe for tender plantsJune 11only 10% chance of frost after

First fall frostSeptember 21median — 10% chance by Sep 9

Growing season115 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 13 and returns around September 29.

From the NOAA station Manassa, CO — 22 miles away, elevation 7,694 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 81120

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 16 – Apr 30

SpinachSow outdoors · Apr 16 – May 7

Broccoli, cabbageStart indoors · Mar 19 – Apr 2

Broccoli, cabbageTransplant · May 7 – May 21

Onion setsPlant outdoors · Apr 30 – May 14

PotatoesPlant outdoors · May 7 – May 21

LettuceSow outdoors · Apr 30 – May 14

Carrots, beetsSow outdoors · May 7 – May 21

TomatoesStart indoors · Apr 2 – Apr 16

TomatoesTransplant · Jun 4 – Jun 18

Peppers, eggplantStart indoors · Mar 19 – Apr 2

Peppers, eggplantTransplant · Jun 11 – Jun 25

BeansSow outdoors · Jun 4 – Jun 18

Sweet cornSow outdoors · Jun 4 – Jun 18

Cucumbers, squashSow outdoors · Jun 4 – Jun 18

Fall lettuce, spinachSow outdoors · Jul 27 – Aug 10

GarlicPlant cloves · Sep 7 – Oct 12

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 28) and first fall frost (Sep 21) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 81120 came on Apr 17 — 20 days earlier than the 1991–2020 average (May 7).

average
May 72026
Apr 17

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 5b in Colorado

546 plants native to the lower 48 states, recorded in Colorado, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. Each links to its USDA PLANTS profile.

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Antonito, CO.

Soil in Antonito, CO

The soil mapped at the center of ZIP 81120 is Seitz — very stony loam, well drained.

TextureVery stony loama good balance for most vegetables

pH6.7neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter0.75%low — add compost

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Seitz very stony loam, 10 to 65 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 81120; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Antonito, CO

Summer high81 °Faverage high, July

Winter low5 °Faverage low, January

Hot days1days a year at 90 °F or more

Freezing nights206nights a year at 32 °F or less

Growing degree days1,589base 50 °F — the season’s usable heat

Longest day14 h 43 mindaylight on June 21

Shortest day9 h 36 mindaylight on December 21

Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully

Precipitation38.2 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Manassa, CO (22 mi away); precipitation: Cumbres Trestle, CO (13 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

5 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

Monte Vista, CO · 27 mi

Colorado planting zones →

Questions about 81120

What planting zone is ZIP code 81120?

ZIP code 81120 (Antonito, CO) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Antonito, CO?

The median last spring frost (32 °F) near 81120 is May 28; after June 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Manassa station.

When is the first frost in Antonito, CO?

The median first fall frost near 81120 is September 21, giving a median frost-free growing season of 115 days.

When should I plant tomatoes in 81120?

Start tomato seeds indoors around Apr 2 – Apr 16 and set transplants outside around Jun 4 – Jun 18, one to three weeks after the median last frost.

How much rain and snow does 81120 get?

About 38.2 inches of precipitation a year (NOAA 1991–2020 normals, Cumbres Trestle station).

How hot do summers get in Antonito, CO?

The average high peaks at 81 °F in July, with about 1 days a year at 90 °F or more.

What kind of soil does 81120 have?

The USDA soil survey maps Seitz at the center of ZIP 81120: very stony loam, well drained, pH about 6.7 (neutral).

Did spring come early in Antonito, CO in 2026?

Spring leaf-out near 81120 came on Apr 17 in 2026, 20 days earlier than the 1991–2020 average (May 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Antonito, CO?

Intermediate onions: the longest day near 81120 is 14 h 43 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 81120 change?

Yes. The 2012 USDA map put 81120 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.