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

Planting zone for 63373 — Portage Des Sioux, MO

ZIP code 63373 (Portage Des Sioux, Saint Charles County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is April 5 and the first fall frost October 27.

Where ZIP 63373 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 5

First frostOct 27

2012 zone6b

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 6b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Portage Des Sioux, 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 Portage Des Sioux, MO

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 5median — 50% chance of a later frost

Safe for tender plantsApril 21only 10% chance of frost after

First fall frostOctober 27median — 10% chance by Oct 13

Growing season203 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 26 and returns around November 6.

From the NOAA station St Charles Co. Airport, MO — 2 miles away, elevation 436 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 63373

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 22 – Mar 8

SpinachSow outdoors · Feb 22 – Mar 15

Broccoli, cabbageStart indoors · Jan 25 – Feb 8

Broccoli, cabbageTransplant · Mar 15 – Mar 29

Onion setsPlant outdoors · Mar 8 – Mar 22

PotatoesPlant outdoors · Mar 15 – Mar 29

LettuceSow outdoors · Mar 8 – Mar 22

Carrots, beetsSow outdoors · Mar 15 – Mar 29

TomatoesStart indoors · Feb 8 – Feb 22

TomatoesTransplant · Apr 12 – Apr 26

Peppers, eggplantStart indoors · Jan 25 – Feb 8

Peppers, eggplantTransplant · Apr 19 – May 3

BeansSow outdoors · Apr 12 – Apr 26

Sweet cornSow outdoors · Apr 12 – Apr 26

Cucumbers, squashSow outdoors · Apr 12 – Apr 26

Fall lettuce, spinachSow outdoors · Sep 1 – Sep 15

GarlicPlant cloves · Oct 13 – Nov 17

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 5) and first fall frost (Oct 27) 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 63373 came on Mar 6 — 11 days earlier than the 1991–2020 average (Mar 17).

average
Mar 172026
Mar 6

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 Portage Des Sioux, MO.

Soil in Portage Des Sioux, MO

The soil mapped at the center of ZIP 63373 is Portage — clay, very poorly drained.

TextureClayholds water and nutrients; slow to drain and warm up

pH6.2slightly acidic; most vegetables like 6.0–7.0

DrainageVery poorly drainedconsider raised beds

Organic matter3.9%moderate

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Portage clay, 0 to 2 percent slopes, occasionally flooded, frequently ponded.

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 63373; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Portage Des Sioux, MO

Summer high89 °Faverage high, July

Winter low22 °Faverage low, January

Hot days44days a year at 90 °F or more

Freezing nights102nights a year at 32 °F or less

Growing degree days4,230base 50 °F — the season’s usable heat

Longest day14 h 54 mindaylight on June 21

Shortest day9 h 26 mindaylight on December 21

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

Precipitation39.4 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: St Charles Co. Airport, MO (2 mi away); precipitation: St Charles Co. Airport, MO (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Saint Charles, MO · 6 mi

620376b

Grafton, IL · 7 mi

630347a

Florissant, MO · 8 mi

620356b

Godfrey, IL · 8 mi

630317a

Florissant, MO · 8 mi

633867a

West Alton, MO · 10 mi

Missouri planting zones →

Questions about 63373

What planting zone is ZIP code 63373?

ZIP code 63373 (Portage Des Sioux, 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 Portage Des Sioux, MO?

The median last spring frost (32 °F) near 63373 is April 5; after April 21 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, St Charles Co. Airport station.

When is the first frost in Portage Des Sioux, MO?

The median first fall frost near 63373 is October 27, giving a median frost-free growing season of 203 days.

When should I plant tomatoes in 63373?

Start tomato seeds indoors around Feb 8 – Feb 22 and set transplants outside around Apr 12 – Apr 26, one to three weeks after the median last frost.

How much rain and snow does 63373 get?

About 39.4 inches of precipitation a year (NOAA 1991–2020 normals, St Charles Co. Airport station).

How hot do summers get in Portage Des Sioux, MO?

The average high peaks at 89 °F in July, with about 44 days a year at 90 °F or more.

What kind of soil does 63373 have?

The USDA soil survey maps Portage at the center of ZIP 63373: clay, very poorly drained, pH about 6.2 (slightly acidic).

Did spring come early in Portage Des Sioux, MO in 2026?

Spring leaf-out near 63373 came on Mar 6 in 2026, 11 days earlier than the 1991–2020 average (Mar 17), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Portage Des Sioux, MO?

Intermediate onions: the longest day near 63373 is 14 h 54 min, so day-neutral types bulb best; long-day varieties may not bulb fully.