Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 63664 — Potosi, MO

ZIP code 63664 (Potosi, Washington County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is April 11 and the first fall frost October 28.

Where ZIP 63664 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.

Zone6b−5 to 0 °F

Coldest night−20.6 to −17.8 °C

Last frostApr 11

First frostOct 28

2012 zone6a

Was 6a 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 6b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Potosi, MO…

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 Potosi, MO

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 11median — 50% chance of a later frost

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

First fall frostOctober 28median — 10% chance by Oct 14

Growing season198 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 31 and returns around November 4.

From the NOAA station Potosi 4 Sw, MO — 4 miles away, elevation 1,106 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 63664

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 28 – Mar 14

SpinachSow outdoors · Feb 28 – Mar 21

Broccoli, cabbageStart indoors · Jan 31 – Feb 14

Broccoli, cabbageTransplant · Mar 21 – Apr 4

Onion setsPlant outdoors · Mar 14 – Mar 28

PotatoesPlant outdoors · Mar 21 – Apr 4

LettuceSow outdoors · Mar 14 – Mar 28

Carrots, beetsSow outdoors · Mar 21 – Apr 4

TomatoesStart indoors · Feb 14 – Feb 28

TomatoesTransplant · Apr 18 – May 2

Peppers, eggplantStart indoors · Jan 31 – Feb 14

Peppers, eggplantTransplant · Apr 25 – May 9

BeansSow outdoors · Apr 18 – May 2

Sweet cornSow outdoors · Apr 18 – May 2

Cucumbers, squashSow outdoors · Apr 18 – May 2

Fall lettuce, spinachSow outdoors · Sep 2 – Sep 16

GarlicPlant cloves · Oct 14 – Nov 18

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 11) and first fall frost (Oct 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 63664 came on Mar 1 — 12 days earlier than the 1991–2020 average (Mar 13).

average
Mar 132026
Mar 1

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 6b in Missouri

525 plants native to the lower 48 states, recorded in Missouri, and rated by the USDA to survive −5 °F or colder — the bottom of zone 6b. 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 Potosi, MO.

Soil in Potosi, MO

The soil mapped at the center of ZIP 63664 is Alred — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH4.3strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter69%high

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Alred-Sonsac complex, 15 to 35 percent slopes, very rocky, very stony.

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 63664; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Potosi, MO

Summer high86 °Faverage high, July

Winter low21 °Faverage low, January

Hot days23days a year at 90 °F or more

Freezing nights103nights a year at 32 °F or less

Growing degree days3,879base 50 °F — the season’s usable heat

Longest day14 h 48 mindaylight on June 21

Shortest day9 h 32 mindaylight on December 21

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

Precipitation45.5 inper year, rain and melted snow

Snowfall12 inper year; 17 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Potosi 4 Sw, MO (4 mi away); precipitation: Potosi 4 Sw, MO (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6b.

636226b

Belgrade, MO · 9 mi

636606b

Mineral Point, MO · 11 mi

636306b

Cadet, MO · 13 mi

636316b

Caledonia, MO · 13 mi

Blackwell, MO · 15 mi

636746b

Tiff, MO · 16 mi

Missouri planting zones →

Questions about 63664

What planting zone is ZIP code 63664?

ZIP code 63664 (Potosi, MO) is in USDA hardiness zone 6b on the 2023 map: the coldest night of an average winter reaches −5 to 0 °F (−20.6 to −17.8 °C).

When is the last frost in Potosi, MO?

The median last spring frost (32 °F) near 63664 is April 11; after April 30 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Potosi 4 Sw station.

When is the first frost in Potosi, MO?

The median first fall frost near 63664 is October 28, giving a median frost-free growing season of 198 days.

When should I plant tomatoes in 63664?

Start tomato seeds indoors around Feb 14 – Feb 28 and set transplants outside around Apr 18 – May 2, one to three weeks after the median last frost.

How much rain and snow does 63664 get?

About 45.5 inches of precipitation a year and 12 inches of snowfall (NOAA 1991–2020 normals, Potosi 4 Sw station).

How hot do summers get in Potosi, MO?

The average high peaks at 86 °F in July, with about 23 days a year at 90 °F or more.

What kind of soil does 63664 have?

The USDA soil survey maps Alred at the center of ZIP 63664: slightly decomposed plant material, well drained, pH about 4.3 (strongly acidic).

Did spring come early in Potosi, MO in 2026?

Spring leaf-out near 63664 came on Mar 1 in 2026, 12 days earlier than the 1991–2020 average (Mar 13), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Potosi, MO?

Intermediate onions: the longest day near 63664 is 14 h 48 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 63664 change?

Yes. The 2012 USDA map put 63664 in zone 6a; the 2023 map puts it in zone 6b. The newer map uses 1991–2020 data and more weather stations.