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

Planting zone for 81101 — Alamosa, CO

ZIP code 81101 (Alamosa, Alamosa County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 30 and the first fall frost September 17.

Where ZIP 81101 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.

Zone4b−25 to −20 °F
Coldest night−31.7 to −28.9 °C
Last frostMay 30
First frostSep 17
2012 zone4b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Alamosa, 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 Alamosa, CO

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 30median — 50% chance of a later frost
Safe for tender plantsJune 13only 10% chance of frost after
First fall frostSeptember 17median — 10% chance by Sep 4
Growing season108 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 16 and returns around September 27.

From the NOAA station Alamosa 1e, CO — within 1 mile, elevation 7,540 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 81101

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 18 – May 2
SpinachSow outdoors · Apr 18 – May 9
Broccoli, cabbageStart indoors · Mar 21 – Apr 4
Broccoli, cabbageTransplant · May 9 – May 23
Onion setsPlant outdoors · May 2 – May 16
PotatoesPlant outdoors · May 9 – May 23
LettuceSow outdoors · May 2 – May 16
Carrots, beetsSow outdoors · May 9 – May 23
TomatoesStart indoors · Apr 4 – Apr 18
TomatoesTransplant · Jun 6 – Jun 20
Peppers, eggplantStart indoors · Mar 21 – Apr 4
Peppers, eggplantTransplant · Jun 13 – Jun 27
BeansSow outdoors · Jun 6 – Jun 20
Sweet cornSow outdoors · Jun 6 – Jun 20
Cucumbers, squashSow outdoors · Jun 6 – Jun 20
Fall lettuce, spinachSow outdoors · Jul 23 – Aug 6
GarlicPlant cloves · Sep 3 – Oct 8
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 30) and first fall frost (Sep 17) 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 81101 came on Mar 23 — 23 days earlier than the 1991–2020 average (Apr 15).

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 4b in Colorado

484 plants native to the lower 48 states, recorded in Colorado, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

Trees 26

American elm120 ft · blooms early spring · medium shade tolerance · to −46 °Fbalsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °Fblack walnut100 ft · blooms late spring · high shade tolerance · to −28 °Fblack willow100 ft · blooms early spring · high shade tolerance · to −58 °Fblue spruce100 ft · blooms late spring · medium shade tolerance · to −38 °F

Shrubs 78

alderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican plum24 ft · blooms mid spring · high shade tolerance · to −38 °Fantelope bitterbrush6 ft · blooms early spring · medium shade tolerance · to −36 °FBarclay's willow15 ft · high shade tolerance · to −43 °F

Wildflowers & perennials 221

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine aster0.3 ft · blooms early summer · medium shade tolerance · to −28 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °F

Grasses 147

Alaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °Falkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °FAlpine Meadow-Foxtail0.5 ft · blooms mid spring · medium shade tolerance · to −33 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Fanalogue sedge1.5 ft · blooms late spring · medium shade tolerance · to −38 °F

Vines 3

riverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °FVirginia creeper1 ft · blooms late spring · medium shade tolerance · to −28 °Fwestern white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °F

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 Alamosa, CO.

Soil in Alamosa, CO

The center of ZIP 81101 is mapped as Sandy alluvial land: built-over ground without natural soil data. Garden soil here is usually imported or disturbed — test before you plant.

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 81101; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Alamosa, CO

Summer high83 °Faverage high, July
Winter low0 °Faverage low, January
Hot days3days a year at 90 °F or more
Freezing nights221nights a year at 32 °F or less
Growing degree days1,533base 50 °F — the season’s usable heat
Longest day14 h 45 mindaylight on June 21
Shortest day9 h 34 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation7.3 inper year, rain and melted snow
Snowfall30 inper year; 51 days with snow on the ground

Average high and low, by month

−10°0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 35 °F, low 0 °F 35°0° JanFebruary: average high 43 °F, low 7 °F 43°7° FebMarch: average high 53 °F, low 17 °F 53°17° MarApril: average high 59 °F, low 26 °F 59°26° AprMay: average high 69 °F, low 34 °F 69°34° MayJune: average high 79 °F, low 42 °F 79°42° JunJuly: average high 83 °F, low 48 °F 83°48° JulAugust: average high 80 °F, low 45 °F 80°45° AugSeptember: average high 75 °F, low 37 °F 75°37° SepOctober: average high 64 °F, low 25 °F 64°25° OctNovember: average high 51 °F, low 13 °F 51°13° NovDecember: average high 37 °F, low 2 °F 37°2° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″January: 0.39 in precipitation, 6.9 in snowfall 0.4❄7 JanFebruary: 0.26 in precipitation, 4.2 in snowfall 0.3❄4 FebMarch: 0.46 in precipitation, 4.3 in snowfall 0.5❄4 MarApril: 0.53 in precipitation, 4.5 in snowfall 0.5❄5 AprMay: 0.65 in precipitation, 0.8 in snowfall 0.7❄1 MayJune: 0.26 in precipitation 0.3 JunJuly: 1.16 in precipitation 1.2 JulAugust: 1.43 in precipitation 1.4 AugSeptember: 0.94 in precipitation 0.9 SepOctober: 0.59 in precipitation, 2 in snowfall 0.6❄2 OctNovember: 0.36 in precipitation, 3.1 in snowfall 0.4❄3 NovDecember: 0.23 in precipitation, 4.2 in snowfall 0.2❄4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Alamosa 1e, CO (within 1 mile); precipitation: Alamosa 1e, CO (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

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

811354b
Homelake, CO · 15 mi
811465a
Mosca, CO · 16 mi
811235a
Blanca, CO · 16 mi
811445a
Monte Vista, CO · 17 mi
811365a
Hooper, CO · 17 mi
811515a
Sanford, CO · 18 mi
811245a
Capulin, CO · 19 mi
811405b
La Jara, CO · 21 mi

Colorado planting zones →

Questions about 81101

What planting zone is ZIP code 81101?

ZIP code 81101 (Alamosa, CO) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in Alamosa, CO?

The median last spring frost (32 °F) near 81101 is May 30; after June 13 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Alamosa 1e station.

When is the first frost in Alamosa, CO?

The median first fall frost near 81101 is September 17, giving a median frost-free growing season of 108 days.

When should I plant tomatoes in 81101?

Start tomato seeds indoors around Apr 4 – Apr 18 and set transplants outside around Jun 6 – Jun 20, one to three weeks after the median last frost.

How much rain and snow does 81101 get?

About 7.3 inches of precipitation a year and 30 inches of snowfall (NOAA 1991–2020 normals, Alamosa 1e station).

How hot do summers get in Alamosa, CO?

The average high peaks at 83 °F in July, with about 3 days a year at 90 °F or more.

Did spring come early in Alamosa, CO in 2026?

Spring leaf-out near 81101 came on Mar 23 in 2026, 23 days earlier than the 1991–2020 average (Apr 15), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Alamosa, CO?

Intermediate onions: the longest day near 81101 is 14 h 45 min, so day-neutral types bulb best; long-day varieties may not bulb fully.