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

Planting zone for 80543 — Milliken, CO

ZIP code 80543 (Milliken, Weld County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 2 and the first fall frost October 8.

Where ZIP 80543 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 2
First frostOct 8
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 Milliken, 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 Milliken, CO

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 2median — 50% chance of a later frost
Safe for tender plantsMay 14only 10% chance of frost after
First fall frostOctober 8median — 10% chance by Sep 26
Growing season159 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 20 and returns around October 18.

From the NOAA station Greeley Unc, CO — 9 miles away, elevation 4,715 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 80543

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 21 – Apr 4
SpinachSow outdoors · Mar 21 – Apr 11
Broccoli, cabbageStart indoors · Feb 21 – Mar 7
Broccoli, cabbageTransplant · Apr 11 – Apr 25
Onion setsPlant outdoors · Apr 4 – Apr 18
PotatoesPlant outdoors · Apr 11 – Apr 25
LettuceSow outdoors · Apr 4 – Apr 18
Carrots, beetsSow outdoors · Apr 11 – Apr 25
TomatoesStart indoors · Mar 7 – Mar 21
TomatoesTransplant · May 9 – May 23
Peppers, eggplantStart indoors · Feb 21 – Mar 7
Peppers, eggplantTransplant · May 16 – May 30
BeansSow outdoors · May 9 – May 23
Sweet cornSow outdoors · May 9 – May 23
Cucumbers, squashSow outdoors · May 9 – May 23
Fall lettuce, spinachSow outdoors · Aug 13 – Aug 27
GarlicPlant cloves · Sep 24 – Oct 29
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 2) and first fall frost (Oct 8) 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 80543 came on Feb 25 — 30 days earlier than the 1991–2020 average (Mar 27).

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 Milliken, CO.

Soil in Milliken, CO

The soil mapped at the center of ZIP 80543 is Colby — loam, well drained.

TextureLoama good balance for most vegetables
pH7.9alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.25%low — add compost
Hydrologic groupBwater soaks in moderately
Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Colby loam, 1 to 3 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 80543; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Milliken, CO

Summer high92 °Faverage high, July
Winter low18 °Faverage low, January
Hot days58days a year at 90 °F or more
Freezing nights153nights a year at 32 °F or less
Growing degree days3,210base 50 °F — the season’s usable heat
Longest day15 h 03 mindaylight on June 21
Shortest day9 h 17 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation14.4 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 44 °F, low 18 °F 44°18° JanFebruary: average high 48 °F, low 20 °F 48°20° FebMarch: average high 59 °F, low 28 °F 59°28° MarApril: average high 66 °F, low 35 °F 66°35° AprMay: average high 75 °F, low 45 °F 75°45° MayJune: average high 86 °F, low 54 °F 86°54° JunJuly: average high 92 °F, low 59 °F 92°59° JulAugust: average high 89 °F, low 57 °F 89°57° AugSeptember: average high 82 °F, low 49 °F 82°49° SepOctober: average high 68 °F, low 37 °F 68°37° OctNovember: average high 54 °F, low 26 °F 54°26° NovDecember: average high 43 °F, low 18 °F 43°18° Dec

Precipitation by month inches

0″1″2″3″January: 0.39 in precipitation 0.4 JanFebruary: 0.39 in precipitation 0.4 FebMarch: 0.92 in precipitation 0.9 MarApril: 1.74 in precipitation 1.7 AprMay: 2.63 in precipitation 2.6 MayJune: 1.79 in precipitation 1.8 JunJuly: 1.54 in precipitation 1.5 JulAugust: 1.44 in precipitation 1.4 AugSeptember: 1.36 in precipitation 1.4 SepOctober: 1.08 in precipitation 1.1 OctNovember: 0.65 in precipitation 0.7 NovDecember: 0.51 in precipitation 0.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Greeley Unc, CO (9 mi away); precipitation: Milliken 1.3 Wsw, CO (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

805345b
Johnstown, CO · 4 mi
806345b
Greeley, CO · 5 mi
806325a
Greeley, CO · 5 mi
806235a
Gilcrest, CO · 6 mi
806205b
Evans, CO · 8 mi
806515b
Platteville, CO · 8 mi
805515b
Windsor, CO · 9 mi
806335b
Greeley, CO · 9 mi

Colorado planting zones →

Questions about 80543

What planting zone is ZIP code 80543?

ZIP code 80543 (Milliken, 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 Milliken, CO?

The median last spring frost (32 °F) near 80543 is May 2; after May 14 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Greeley Unc station.

When is the first frost in Milliken, CO?

The median first fall frost near 80543 is October 8, giving a median frost-free growing season of 159 days.

When should I plant tomatoes in 80543?

Start tomato seeds indoors around Mar 7 – Mar 21 and set transplants outside around May 9 – May 23, one to three weeks after the median last frost.

How much rain and snow does 80543 get?

About 14.4 inches of precipitation a year (NOAA 1991–2020 normals, Milliken 1.3 Wsw station).

How hot do summers get in Milliken, CO?

The average high peaks at 92 °F in July, with about 58 days a year at 90 °F or more.

What kind of soil does 80543 have?

The USDA soil survey maps Colby at the center of ZIP 80543: loam, well drained, pH about 7.9 (alkaline).

Did spring come early in Milliken, CO in 2026?

Spring leaf-out near 80543 came on Feb 25 in 2026, 30 days earlier than the 1991–2020 average (Mar 27), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Milliken, CO?

Long-day onions: the longest day near 80543 is 15 h 03 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).