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

Planting zone for 81321 — Cortez, CO

ZIP code 81321 (Cortez, Montezuma County) is in USDA zone 7a: the coldest winter night averages 0 to 5 °F. The median last spring frost is May 27 and the first fall frost September 28.

Where ZIP 81321 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.

Zone7a0 to 5 °F
Coldest night−17.8 to −15 °C
Last frostMay 27
First frostSep 28
2012 zone6a

Was 6a on the 2012 map — a full zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 7a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Cortez, 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 Cortez, CO

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 27median — 50% chance of a later frost
Safe for tender plantsJune 11only 10% chance of frost after
First fall frostSeptember 28median — 10% chance by Sep 17
Growing season125 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 8 and returns around October 7.

From the NOAA station Cortez Montezuma Co. Airport, CO — 6 miles away, elevation 5,916 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 81321

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 15 – Apr 29
SpinachSow outdoors · Apr 15 – May 6
Broccoli, cabbageStart indoors · Mar 18 – Apr 1
Broccoli, cabbageTransplant · May 6 – May 20
Onion setsPlant outdoors · Apr 29 – May 13
PotatoesPlant outdoors · May 6 – May 20
LettuceSow outdoors · Apr 29 – May 13
Carrots, beetsSow outdoors · May 6 – May 20
TomatoesStart indoors · Apr 1 – Apr 15
TomatoesTransplant · Jun 3 – Jun 17
Peppers, eggplantStart indoors · Mar 18 – Apr 1
Peppers, eggplantTransplant · Jun 10 – Jun 24
BeansSow outdoors · Jun 3 – Jun 17
Sweet cornSow outdoors · Jun 3 – Jun 17
Cucumbers, squashSow outdoors · Jun 3 – Jun 17
Fall lettuce, spinachSow outdoors · Aug 3 – Aug 17
GarlicPlant cloves · Sep 14 – Oct 19
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 27) and first fall frost (Sep 28) 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 81321 came on Mar 17 — 10 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 7a in Colorado

573 plants native to the lower 48 states, recorded in Colorado, and rated by the USDA to survive 0 °F or colder — the bottom of zone 7a. Each links to its USDA PLANTS profile.

Trees 28

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 107

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 254

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 171

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 4

riverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Ftrumpet creeper2 ft · blooms summer · high shade tolerance · to −13 °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 Cortez, CO.

Soil in Cortez, CO

The soil mapped at the center of ZIP 81321 is Romberg — very stony loam, well drained.

TextureVery stony loama good balance for most vegetables
pH7.4slightly alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Romberg, extremely stony-Crosscan, very bouldery-Rock outcrop complex, 25 to 80 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 81321; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Cortez, CO

Summer high91 °Faverage high, July
Winter low14 °Faverage low, January
Hot days48days a year at 90 °F or more
Freezing nights191nights a year at 32 °F or less
Growing degree days2,432base 50 °F — the season’s usable heat
Longest day14 h 44 mindaylight on June 21
Shortest day9 h 35 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation11.7 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 42 °F, low 14 °F 42°14° JanFebruary: average high 47 °F, low 19 °F 47°19° FebMarch: average high 57 °F, low 24 °F 57°24° MarApril: average high 64 °F, low 30 °F 64°30° AprMay: average high 75 °F, low 37 °F 75°37° MayJune: average high 86 °F, low 45 °F 86°45° JunJuly: average high 91 °F, low 54 °F 91°54° JulAugust: average high 87 °F, low 52 °F 87°52° AugSeptember: average high 80 °F, low 43 °F 80°43° SepOctober: average high 67 °F, low 31 °F 67°31° OctNovember: average high 53 °F, low 22 °F 53°22° NovDecember: average high 42 °F, low 15 °F 42°15° Dec

Precipitation by month inches

0″1″2″January: 1.07 in precipitation 1.1 JanFebruary: 1.01 in precipitation 1.0 FebMarch: 0.84 in precipitation 0.8 MarApril: 0.75 in precipitation 0.8 AprMay: 0.74 in precipitation 0.7 MayJune: 0.29 in precipitation 0.3 JunJuly: 1.14 in precipitation 1.1 JulAugust: 1.59 in precipitation 1.6 AugSeptember: 1.58 in precipitation 1.6 SepOctober: 1.06 in precipitation 1.1 OctNovember: 0.79 in precipitation 0.8 NovDecember: 0.80 in precipitation 0.8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Cortez Montezuma Co. Airport, CO (6 mi away); precipitation: Cortez Montezuma Co. Airport, CO (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

813316b
Pleasant View, CO · 13 mi
813347a
Towaoc, CO · 13 mi
813276b
Lewis, CO · 15 mi
813307a
Mesa Verde National Park, CO · 15 mi
813356b
Yellow Jacket, CO · 16 mi
813286a
Mancos, CO · 22 mi
813246b
Dove Creek, CO · 27 mi
813206b
Cahone, CO · 28 mi

Colorado planting zones →

Questions about 81321

What planting zone is ZIP code 81321?

ZIP code 81321 (Cortez, CO) is in USDA hardiness zone 7a on the 2023 map: the coldest night of an average winter reaches 0 to 5 °F (−17.8 to −15 °C).

When is the last frost in Cortez, CO?

The median last spring frost (32 °F) near 81321 is May 27; after June 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Cortez Montezuma Co. Airport station.

When is the first frost in Cortez, CO?

The median first fall frost near 81321 is September 28, giving a median frost-free growing season of 125 days.

When should I plant tomatoes in 81321?

Start tomato seeds indoors around Apr 1 – Apr 15 and set transplants outside around Jun 3 – Jun 17, one to three weeks after the median last frost.

How much rain and snow does 81321 get?

About 11.7 inches of precipitation a year (NOAA 1991–2020 normals, Cortez Montezuma Co. Airport station).

How hot do summers get in Cortez, CO?

The average high peaks at 91 °F in July, with about 48 days a year at 90 °F or more.

What kind of soil does 81321 have?

The USDA soil survey maps Romberg at the center of ZIP 81321: very stony loam, well drained, pH about 7.4 (slightly alkaline).

Did spring come early in Cortez, CO in 2026?

Spring leaf-out near 81321 came on Mar 17 in 2026, 10 days earlier than the 1991–2020 average (Mar 27), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Cortez, CO?

Intermediate onions: the longest day near 81321 is 14 h 44 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 81321 change?

Yes. The 2012 USDA map put 81321 in zone 6a; the 2023 map puts it in zone 7a. The newer map uses 1991–2020 data and more weather stations.