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

Planting zone for 81433 — Silverton, CO

ZIP code 81433 (Silverton, San Juan County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is June 15 and the first fall frost September 11.

Where ZIP 81433 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.

Zone5a−20 to −15 °F

Coldest night−28.9 to −26.1 °C

Last frostJun 15

First frostSep 11

2012 zone4b

Was 4b 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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Silverton, 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 Silverton, CO

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 15median — 50% chance of a later frost

Safe for tender plantsJune 30only 10% chance of frost after

First fall frostSeptember 11median — 10% chance by Aug 27

Growing season85 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 31 and returns around September 23.

From the NOAA station Rio Grande Rsvr, CO — 17 miles away, elevation 9,492 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 81433

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · May 4 – May 18

SpinachSow outdoors · May 4 – May 25

Broccoli, cabbageStart indoors · Apr 6 – Apr 20

Broccoli, cabbageTransplant · May 25 – Jun 8

Onion setsPlant outdoors · May 18 – Jun 1

PotatoesPlant outdoors · May 25 – Jun 8

LettuceSow outdoors · May 18 – Jun 1

Carrots, beetsSow outdoors · May 25 – Jun 8

TomatoesStart indoors · Apr 20 – May 4

TomatoesTransplant · Jun 22 – Jul 6

Peppers, eggplantStart indoors · Apr 6 – Apr 20

Peppers, eggplantTransplant · Jun 29 – Jul 13

BeansSow outdoors · Jun 22 – Jul 6

Sweet cornSow outdoors · Jun 22 – Jul 6

Cucumbers, squashSow outdoors · Jun 22 – Jul 6

Fall lettuce, spinachSow outdoors · Jul 17 – Jul 31

GarlicPlant cloves · Aug 28 – Oct 2

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 15) and first fall frost (Sep 11) 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 81433 came on May 24 — 8 days earlier than the 1991–2020 average (Jun 1).

average
Jun 12026
May 24

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 5a in Colorado

532 plants native to the lower 48 states, recorded in Colorado, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. 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 Silverton, CO.

Soil in Silverton, CO

The soil mapped at the center of ZIP 81433 is Snowdon — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH5.8moderately acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter85%high

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Snowdon-Rock outcrop complex, 30 to 65 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 81433; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Silverton, CO

Summer high75 °Faverage high, July

Winter low−6 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights272nights a year at 32 °F or less

Growing degree days447base 50 °F — the season’s usable heat

Longest day14 h 47 mindaylight on June 21

Shortest day9 h 33 mindaylight on December 21

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

Precipitation39.2 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: Silverton, CO (7 mi away); precipitation: Beartown, CO (4 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.

Lake City, CO · 19 mi

814275b

Ouray, CO · 21 mi

814355b

Telluride, CO · 21 mi

Colorado planting zones →

Questions about 81433

What planting zone is ZIP code 81433?

ZIP code 81433 (Silverton, CO) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Silverton, CO?

The median last spring frost (32 °F) near 81433 is June 15; after June 30 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Rio Grande Rsvr station.

When is the first frost in Silverton, CO?

The median first fall frost near 81433 is September 11, giving a median frost-free growing season of 85 days.

When should I plant tomatoes in 81433?

Start tomato seeds indoors around Apr 20 – May 4 and set transplants outside around Jun 22 – Jul 6, one to three weeks after the median last frost.

How much rain and snow does 81433 get?

About 39.2 inches of precipitation a year (NOAA 1991–2020 normals, Beartown station).

How hot do summers get in Silverton, CO?

The average high peaks at 75 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 81433 have?

The USDA soil survey maps Snowdon at the center of ZIP 81433: slightly decomposed plant material, well drained, pH about 5.8 (moderately acidic).

Did spring come early in Silverton, CO in 2026?

Spring leaf-out near 81433 came on May 24 in 2026, 8 days earlier than the 1991–2020 average (Jun 1), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Silverton, CO?

Intermediate onions: the longest day near 81433 is 14 h 47 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 81433 change?

Yes. The 2012 USDA map put 81433 in zone 4b; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.