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

Planting zone for 61274 — Osco, IL

ZIP code 61274 (Osco, Henry County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 20 and the first fall frost October 20.

Where ZIP 61274 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 20

First frostOct 20

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 Osco, IL…

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 Osco, IL

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 20median — 50% chance of a later frost

Safe for tender plantsMay 6only 10% chance of frost after

First fall frostOctober 20median — 10% chance by Oct 5

Growing season180 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 9 and returns around October 30.

From the NOAA station Geneseo, IL — 9 miles away, elevation 640 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 61274

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 9 – Mar 23

SpinachSow outdoors · Mar 9 – Mar 30

Broccoli, cabbageStart indoors · Feb 9 – Feb 23

Broccoli, cabbageTransplant · Mar 30 – Apr 13

Onion setsPlant outdoors · Mar 23 – Apr 6

PotatoesPlant outdoors · Mar 30 – Apr 13

LettuceSow outdoors · Mar 23 – Apr 6

Carrots, beetsSow outdoors · Mar 30 – Apr 13

TomatoesStart indoors · Feb 23 – Mar 9

TomatoesTransplant · Apr 27 – May 11

Peppers, eggplantStart indoors · Feb 9 – Feb 23

Peppers, eggplantTransplant · May 4 – May 18

BeansSow outdoors · Apr 27 – May 11

Sweet cornSow outdoors · Apr 27 – May 11

Cucumbers, squashSow outdoors · Apr 27 – May 11

Fall lettuce, spinachSow outdoors · Aug 25 – Sep 8

GarlicPlant cloves · Oct 6 – Nov 10

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 20) and first fall frost (Oct 20) 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 61274 came on Mar 19 — 17 days earlier than the 1991–2020 average (Apr 5).

average
Apr 52026
Mar 19

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 5b in Illinois

584 plants native to the lower 48 states, recorded in Illinois, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. 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 Osco, IL.

Soil in Osco, IL

The soil mapped at the center of ZIP 61274 is Muscatune — silt loam, somewhat poorly drained.

TextureSilt loama good balance for most vegetables

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

DrainageSomewhat poorly drainedconsider raised beds

Organic matter4.5%moderate

Hydrologic groupB/Dmoderate when drained; wet otherwise

Farmland classprime farmlandUSDA classification

Map unit: Muscatune silt loam, 0 to 2 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 61274; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Osco, IL

Summer high86 °Faverage high, July

Winter low15 °Faverage low, January

Hot days22days a year at 90 °F or more

Freezing nights126nights a year at 32 °F or less

Growing degree days3,426base 50 °F — the season’s usable heat

Longest day15 h 10 mindaylight on June 21

Shortest day9 h 11 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation38.7 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: Geneseo, IL (9 mi away); precipitation: Coal Valley 1.9 Se, IL (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

Lynn Center, IL · 7 mi

Coal Valley, IL · 9 mi

Illinois planting zones →

Questions about 61274

What planting zone is ZIP code 61274?

ZIP code 61274 (Osco, IL) 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 Osco, IL?

The median last spring frost (32 °F) near 61274 is April 20; after May 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Geneseo station.

When is the first frost in Osco, IL?

The median first fall frost near 61274 is October 20, giving a median frost-free growing season of 180 days.

When should I plant tomatoes in 61274?

Start tomato seeds indoors around Feb 23 – Mar 9 and set transplants outside around Apr 27 – May 11, one to three weeks after the median last frost.

How much rain and snow does 61274 get?

About 38.7 inches of precipitation a year (NOAA 1991–2020 normals, Coal Valley 1.9 Se station).

How hot do summers get in Osco, IL?

The average high peaks at 86 °F in July, with about 22 days a year at 90 °F or more.

What kind of soil does 61274 have?

The USDA soil survey maps Muscatune at the center of ZIP 61274: silt loam, somewhat poorly drained, pH about 6.2 (slightly acidic).

Did spring come early in Osco, IL in 2026?

Spring leaf-out near 61274 came on Mar 19 in 2026, 17 days earlier than the 1991–2020 average (Apr 5), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Osco, IL?

Long-day onions: the longest day near 61274 is 15 h 10 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).