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

Planting zone for 81021 — Arlington, CO

ZIP code 81021 (Arlington, Kiowa County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 3 and the first fall frost October 7.

Where ZIP 81021 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 3
First frostOct 7
2012 zone5b

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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Arlington, 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 Arlington, CO

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 3median — 50% chance of a later frost
Safe for tender plantsMay 16only 10% chance of frost after
First fall frostOctober 7median — 10% chance by Sep 27
Growing season155 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 24 and returns around October 16.

From the NOAA station Ordway 21 N, CO — 19 miles away, elevation 4,767 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 81021

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 22 – Apr 5
SpinachSow outdoors · Mar 22 – Apr 12
Broccoli, cabbageStart indoors · Feb 22 – Mar 8
Broccoli, cabbageTransplant · Apr 12 – Apr 26
Onion setsPlant outdoors · Apr 5 – Apr 19
PotatoesPlant outdoors · Apr 12 – Apr 26
LettuceSow outdoors · Apr 5 – Apr 19
Carrots, beetsSow outdoors · Apr 12 – Apr 26
TomatoesStart indoors · Mar 8 – Mar 22
TomatoesTransplant · May 10 – May 24
Peppers, eggplantStart indoors · Feb 22 – Mar 8
Peppers, eggplantTransplant · May 17 – May 31
BeansSow outdoors · May 10 – May 24
Sweet cornSow outdoors · May 10 – May 24
Cucumbers, squashSow outdoors · May 10 – May 24
Fall lettuce, spinachSow outdoors · Aug 12 – Aug 26
GarlicPlant cloves · Sep 23 – Oct 28
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 3) and first fall frost (Oct 7) 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 81021 came on Feb 26 — 18 days earlier than the 1991–2020 average (Mar 16).

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.

Trees 27

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 98

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 °FApache plume6 ft · blooms late spring · high shade tolerance · to −23 °F

Wildflowers & perennials 246

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 163

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 Arlington, CO.

Soil in Arlington, CO

The soil mapped at the center of ZIP 81021 is Singerton — loam, well drained.

TextureLoama good balance for most vegetables
pH7.9alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter0.75%low — add compost
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Singerton-Pultney complex, 1 to 10 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 81021; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Arlington, CO

Summer high93 °Faverage high, July
Winter low13 °Faverage low, January
Hot days63days a year at 90 °F or more
Freezing nights172nights a year at 32 °F or less
Growing degree days3,280base 50 °F — the season’s usable heat
Longest day14 h 51 mindaylight on June 21
Shortest day9 h 29 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation14.5 inper year, rain and melted snow
Snowfall27 inper year; 18 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 46 °F, low 13 °F 46°13° JanFebruary: average high 48 °F, low 17 °F 48°17° FebMarch: average high 58 °F, low 25 °F 58°25° MarApril: average high 66 °F, low 33 °F 66°33° AprMay: average high 76 °F, low 44 °F 76°44° MayJune: average high 88 °F, low 54 °F 88°54° JunJuly: average high 93 °F, low 60 °F 93°60° JulAugust: average high 90 °F, low 58 °F 90°58° AugSeptember: average high 83 °F, low 48 °F 83°48° SepOctober: average high 69 °F, low 34 °F 69°34° OctNovember: average high 55 °F, low 23 °F 55°23° NovDecember: average high 45 °F, low 14 °F 45°14° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.29 in precipitation, 3.5 in snowfall 0.3❄4 JanFebruary: 0.31 in precipitation, 3.4 in snowfall 0.3❄3 FebMarch: 0.77 in precipitation, 5.7 in snowfall 0.8❄6 MarApril: 1.25 in precipitation, 3.5 in snowfall 1.3❄4 AprMay: 1.91 in precipitation, 0.2 in snowfall 1.9 MayJune: 1.76 in precipitation 1.8 JunJuly: 2.80 in precipitation 2.8 JulAugust: 2.57 in precipitation 2.6 AugSeptember: 1.00 in precipitation, 0.1 in snowfall 1.0 SepOctober: 1.02 in precipitation, 2.4 in snowfall 1.0❄2 OctNovember: 0.42 in precipitation, 4 in snowfall 0.4❄4 NovDecember: 0.36 in precipitation, 4.4 in snowfall 0.4❄4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Ordway 21 N, CO (19 mi away); precipitation: Haswell, CO (12 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

810765b
Sugar City, CO · 13 mi
810455b
Haswell, CO · 16 mi
808235b
Karval, CO · 17 mi
810635b
Ordway, CO · 21 mi
810306a
Cheraw, CO · 23 mi
810926a
Wiley, CO · 29 mi
810345b
Crowley, CO · 30 mi
810776a
Swink, CO · 30 mi

Colorado planting zones →

Questions about 81021

What planting zone is ZIP code 81021?

ZIP code 81021 (Arlington, 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 Arlington, CO?

The median last spring frost (32 °F) near 81021 is May 3; after May 16 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Ordway 21 N station.

When is the first frost in Arlington, CO?

The median first fall frost near 81021 is October 7, giving a median frost-free growing season of 155 days.

When should I plant tomatoes in 81021?

Start tomato seeds indoors around Mar 8 – Mar 22 and set transplants outside around May 10 – May 24, one to three weeks after the median last frost.

How much rain and snow does 81021 get?

About 14.5 inches of precipitation a year and 27 inches of snowfall (NOAA 1991–2020 normals, Haswell station).

How hot do summers get in Arlington, CO?

The average high peaks at 93 °F in July, with about 63 days a year at 90 °F or more.

What kind of soil does 81021 have?

The USDA soil survey maps Singerton at the center of ZIP 81021: loam, well drained, pH about 7.9 (alkaline).

Did spring come early in Arlington, CO in 2026?

Spring leaf-out near 81021 came on Feb 26 in 2026, 18 days earlier than the 1991–2020 average (Mar 16), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Arlington, CO?

Intermediate onions: the longest day near 81021 is 14 h 51 min, so day-neutral types bulb best; long-day varieties may not bulb fully.