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

Planting zone for 64661 — Mercer, MO

ZIP code 64661 (Mercer, Mercer County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 25 and the first fall frost October 15.

Where ZIP 64661 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.

Zone5b−15 to −10 °F
Coldest night−26.1 to −23.3 °C
Last frostApr 25
First frostOct 15
2012 zone5b

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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Mercer, 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 Mercer, MO

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 25median — 50% chance of a later frost
Safe for tender plantsMay 8only 10% chance of frost after
First fall frostOctober 15median — 10% chance by Sep 30
Growing season174 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 14 and returns around October 26.

From the NOAA station Princeton, MO — 10 miles away, elevation 981 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 64661

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 14 – Mar 28
SpinachSow outdoors · Mar 14 – Apr 4
Broccoli, cabbageStart indoors · Feb 14 – Feb 28
Broccoli, cabbageTransplant · Apr 4 – Apr 18
Onion setsPlant outdoors · Mar 28 – Apr 11
PotatoesPlant outdoors · Apr 4 – Apr 18
LettuceSow outdoors · Mar 28 – Apr 11
Carrots, beetsSow outdoors · Apr 4 – Apr 18
TomatoesStart indoors · Feb 28 – Mar 14
TomatoesTransplant · May 2 – May 16
Peppers, eggplantStart indoors · Feb 14 – Feb 28
Peppers, eggplantTransplant · May 9 – May 23
BeansSow outdoors · May 2 – May 16
Sweet cornSow outdoors · May 2 – May 16
Cucumbers, squashSow outdoors · May 2 – May 16
Fall lettuce, spinachSow outdoors · Aug 20 – Sep 3
GarlicPlant cloves · Oct 1 – Nov 5
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 25) and first fall frost (Oct 15) 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 64661 came on Mar 11 — 19 days earlier than the 1991–2020 average (Mar 30).

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).

Soil in Mercer, MO

The soil mapped at the center of ZIP 64661 is Lamoni — clay loam, somewhat poorly drained.

TextureClay loamholds water and nutrients; slow to drain and warm up
pH6.1slightly acidic; most vegetables like 6.0–7.0
DrainageSomewhat poorly drainedconsider raised beds
Organic matter2%moderate
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classPrime farmland if drainedUSDA classification

Map unit: Lamoni clay loam, 5 to 9 percent slopes, eroded.

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 64661; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mercer, MO

Summer high86 °Faverage high, July
Winter low15 °Faverage low, January
Hot days24days a year at 90 °F or more
Freezing nights127nights a year at 32 °F or less
Growing degree days3,378base 50 °F — the season’s usable heat
Longest day15 h 04 mindaylight on June 21
Shortest day9 h 16 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation39.9 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 34 °F, low 15 °F 34°15° JanFebruary: average high 39 °F, low 18 °F 39°18° FebMarch: average high 51 °F, low 29 °F 51°29° MarApril: average high 63 °F, low 39 °F 63°39° AprMay: average high 72 °F, low 50 °F 72°50° MayJune: average high 81 °F, low 61 °F 81°61° JunJuly: average high 86 °F, low 65 °F 86°65° JulAugust: average high 84 °F, low 63 °F 84°63° AugSeptember: average high 77 °F, low 54 °F 77°54° SepOctober: average high 65 °F, low 42 °F 65°42° OctNovember: average high 51 °F, low 30 °F 51°30° NovDecember: average high 38 °F, low 20 °F 38°20° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 1.11 in precipitation 1.1 JanFebruary: 1.64 in precipitation 1.6 FebMarch: 2.37 in precipitation 2.4 MarApril: 3.78 in precipitation 3.8 AprMay: 5.59 in precipitation 5.6 MayJune: 5.19 in precipitation 5.2 JunJuly: 4.36 in precipitation 4.4 JulAugust: 4.71 in precipitation 4.7 AugSeptember: 4.45 in precipitation 4.5 SepOctober: 3.26 in precipitation 3.3 OctNovember: 1.91 in precipitation 1.9 NovDecember: 1.55 in precipitation 1.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Princeton, MO (10 mi away); precipitation: Princeton 1.4 Nne, MO (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

501475b
Lineville, IA · 6 mi
500525b
Clio, IA · 8 mi
500085b
Allerton, IA · 12 mi
646735b
Princeton, MO · 12 mi
646675b
Newtown, MO · 13 mi
646325b
Cainsville, MO · 14 mi
500655b
Davis City, IA · 14 mi
646555b
Lucerne, MO · 15 mi

Missouri planting zones →

Questions about 64661

What planting zone is ZIP code 64661?

ZIP code 64661 (Mercer, MO) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Mercer, MO?

The median last spring frost (32 °F) near 64661 is April 25; after May 8 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Princeton station.

When is the first frost in Mercer, MO?

The median first fall frost near 64661 is October 15, giving a median frost-free growing season of 174 days.

When should I plant tomatoes in 64661?

Start tomato seeds indoors around Feb 28 – Mar 14 and set transplants outside around May 2 – May 16, one to three weeks after the median last frost.

How much rain and snow does 64661 get?

About 39.9 inches of precipitation a year (NOAA 1991–2020 normals, Princeton 1.4 Nne station).

How hot do summers get in Mercer, MO?

The average high peaks at 86 °F in July, with about 24 days a year at 90 °F or more.

What kind of soil does 64661 have?

The USDA soil survey maps Lamoni at the center of ZIP 64661: clay loam, somewhat poorly drained, pH about 6.1 (slightly acidic).

Did spring come early in Mercer, MO in 2026?

Spring leaf-out near 64661 came on Mar 11 in 2026, 19 days earlier than the 1991–2020 average (Mar 30), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Mercer, MO?

Long-day onions: the longest day near 64661 is 15 h 04 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).