Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 30, 2026

Planting zone for 81621 — Basalt, CO

ZIP code 81621 (Basalt, Eagle County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 31 and the first fall frost September 23.

Where ZIP 81621 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.

Zone6a−10 to −5 °F

Coldest night−23.3 to −20.6 °C

Last frostMay 31

First frostSep 23

2012 zone5b

Was 5b 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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Basalt, 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 Basalt, CO

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 31median — 50% chance of a later frost

Safe for tender plantsJune 14only 10% chance of frost after

First fall frostSeptember 23median — 10% chance by Sep 11

Growing season114 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 13 and returns around October 2.

From the NOAA station Aspen Pitkin Co. Airport, CO — 11 miles away, elevation 7,720 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 81621

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 19 – May 3

SpinachSow outdoors · Apr 19 – May 10

Broccoli, cabbageStart indoors · Mar 22 – Apr 5

Broccoli, cabbageTransplant · May 10 – May 24

Onion setsPlant outdoors · May 3 – May 17

PotatoesPlant outdoors · May 10 – May 24

LettuceSow outdoors · May 3 – May 17

Carrots, beetsSow outdoors · May 10 – May 24

TomatoesStart indoors · Apr 5 – Apr 19

TomatoesTransplant · Jun 7 – Jun 21

Peppers, eggplantStart indoors · Mar 22 – Apr 5

Peppers, eggplantTransplant · Jun 14 – Jun 28

BeansSow outdoors · Jun 7 – Jun 21

Sweet cornSow outdoors · Jun 7 – Jun 21

Cucumbers, squashSow outdoors · Jun 7 – Jun 21

Fall lettuce, spinachSow outdoors · Jul 29 – Aug 12

GarlicPlant cloves · Sep 9 – Oct 14

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 31) and first fall frost (Sep 23) 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 81621 came on Mar 31 — 25 days earlier than the 1991–2020 average (Apr 25).

average
Apr 252026
Mar 31

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 6a in Colorado

563 plants native to the lower 48 states, recorded in Colorado, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. 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 Basalt, CO.

Soil in Basalt, CO

The soil mapped at the center of ZIP 81621 is Subwell family — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH5.0strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter75%high

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Subwell family-Endoaquolls association, 0 to 15 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 81621; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Basalt, CO

Summer high81 °Faverage high, July

Winter low4 °Faverage low, January

Hot days4days a year at 90 °F or more

Freezing nights272nights a year at 32 °F or less

Growing degree days916base 50 °F — the season’s usable heat

Longest day14 h 57 mindaylight on June 21

Shortest day9 h 23 mindaylight on December 21

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

Precipitation19.7 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: Meredith, CO (7 mi away); precipitation: Basalt 5.8 E, CO (2 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.

816565b

Woody Creek, CO · 8 mi

816155b

Snowmass Village, CO · 12 mi

Carbondale, CO · 18 mi

Colorado planting zones →

Questions about 81621

What planting zone is ZIP code 81621?

ZIP code 81621 (Basalt, CO) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Basalt, CO?

The median last spring frost (32 °F) near 81621 is May 31; after June 14 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Aspen Pitkin Co. Airport station.

When is the first frost in Basalt, CO?

The median first fall frost near 81621 is September 23, giving a median frost-free growing season of 114 days.

When should I plant tomatoes in 81621?

Start tomato seeds indoors around Apr 5 – Apr 19 and set transplants outside around Jun 7 – Jun 21, one to three weeks after the median last frost.

How much rain and snow does 81621 get?

About 19.7 inches of precipitation a year (NOAA 1991–2020 normals, Basalt 5.8 E station).

How hot do summers get in Basalt, CO?

The average high peaks at 81 °F in July, with about 4 days a year at 90 °F or more.

What kind of soil does 81621 have?

The USDA soil survey maps Subwell family at the center of ZIP 81621: slightly decomposed plant material, well drained, pH about 5.0 (strongly acidic).

Did spring come early in Basalt, CO in 2026?

Spring leaf-out near 81621 came on Mar 31 in 2026, 25 days earlier than the 1991–2020 average (Apr 25), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Basalt, CO?

Intermediate onions: the longest day near 81621 is 14 h 57 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 81621 change?

Yes. The 2012 USDA map put 81621 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.