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

Planting zone for 61285 — Thomson, IL

ZIP code 61285 (Thomson, Carroll County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 13 and the first fall frost October 26.

Where ZIP 61285 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 13

First frostOct 26

2012 zone5a

Was 5a 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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Thomson, 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 Thomson, IL

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 13median — 50% chance of a later frost

Safe for tender plantsApril 28only 10% chance of frost after

First fall frostOctober 26median — 10% chance by Oct 13

Growing season195 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 4 and returns around November 3.

From the NOAA station Fulton L&D #13, IL — 7 miles away, elevation 591 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 61285

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 2 – Mar 16

SpinachSow outdoors · Mar 2 – Mar 23

Broccoli, cabbageStart indoors · Feb 2 – Feb 16

Broccoli, cabbageTransplant · Mar 23 – Apr 6

Onion setsPlant outdoors · Mar 16 – Mar 30

PotatoesPlant outdoors · Mar 23 – Apr 6

LettuceSow outdoors · Mar 16 – Mar 30

Carrots, beetsSow outdoors · Mar 23 – Apr 6

TomatoesStart indoors · Feb 16 – Mar 2

TomatoesTransplant · Apr 20 – May 4

Peppers, eggplantStart indoors · Feb 2 – Feb 16

Peppers, eggplantTransplant · Apr 27 – May 11

BeansSow outdoors · Apr 20 – May 4

Sweet cornSow outdoors · Apr 20 – May 4

Cucumbers, squashSow outdoors · Apr 20 – May 4

Fall lettuce, spinachSow outdoors · Aug 31 – Sep 14

GarlicPlant cloves · Oct 12 – Nov 16

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 13) and first fall frost (Oct 26) 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 61285 came on Mar 28 — 10 days earlier than the 1991–2020 average (Apr 7).

average
Apr 72026
Mar 28

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 Thomson, IL.

Soil in Thomson, IL

The soil mapped at the center of ZIP 61285 is Sawmill — silty clay loam, poorly drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up

pH6.9neutral; most vegetables like 6.0–7.0

DrainagePoorly drainedconsider raised beds

Organic matter3%moderate

Hydrologic groupB/Dmoderate when drained; wet otherwise

Farmland classPrime farmland if drainedUSDA classification

Map unit: Sawmill silty clay loam, 0 to 2 percent slopes, rarely flooded.

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 61285; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Thomson, IL

Summer high84 °Faverage high, July

Winter low14 °Faverage low, January

Hot days13days a year at 90 °F or more

Freezing nights132nights a year at 32 °F or less

Growing degree days3,245base 50 °F — the season’s usable heat

Longest day15 h 14 mindaylight on June 21

Shortest day9 h 07 mindaylight on December 21

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

Precipitation34.3 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: Fulton L&D #13, IL (7 mi away); precipitation: Fulton L&D #13, IL (7 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.

Teeds Grove, IA · 9 mi

610745a

Savanna, IL · 9 mi

610535a

Mount Carroll, IL · 10 mi

Illinois planting zones →

Questions about 61285

What planting zone is ZIP code 61285?

ZIP code 61285 (Thomson, 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 Thomson, IL?

The median last spring frost (32 °F) near 61285 is April 13; after April 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Fulton L&D #13 station.

When is the first frost in Thomson, IL?

The median first fall frost near 61285 is October 26, giving a median frost-free growing season of 195 days.

When should I plant tomatoes in 61285?

Start tomato seeds indoors around Feb 16 – Mar 2 and set transplants outside around Apr 20 – May 4, one to three weeks after the median last frost.

How much rain and snow does 61285 get?

About 34.3 inches of precipitation a year (NOAA 1991–2020 normals, Fulton L&D #13 station).

How hot do summers get in Thomson, IL?

The average high peaks at 84 °F in July, with about 13 days a year at 90 °F or more.

What kind of soil does 61285 have?

The USDA soil survey maps Sawmill at the center of ZIP 61285: silty clay loam, poorly drained, pH about 6.9 (neutral).

Did spring come early in Thomson, IL in 2026?

Spring leaf-out near 61285 came on Mar 28 in 2026, 10 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Thomson, IL?

Long-day onions: the longest day near 61285 is 15 h 14 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 61285 change?

Yes. The 2012 USDA map put 61285 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.