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

Planting zone for 60552 — Somonauk, IL

ZIP code 60552 (Somonauk, DeKalb County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 28 and the first fall frost October 13.

Where ZIP 60552 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 28
First frostOct 13
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 Somonauk, 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 Somonauk, IL

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 28median — 50% chance of a later frost
Safe for tender plantsMay 11only 10% chance of frost after
First fall frostOctober 13median — 10% chance by Sep 27
Growing season166 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 18 and returns around October 23.

From the NOAA station Chicago Aurora Municipal Airport, IL — 14 miles away, elevation 709 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 60552

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 17 – Mar 31
SpinachSow outdoors · Mar 17 – Apr 7
Broccoli, cabbageStart indoors · Feb 17 – Mar 3
Broccoli, cabbageTransplant · Apr 7 – Apr 21
Onion setsPlant outdoors · Mar 31 – Apr 14
PotatoesPlant outdoors · Apr 7 – Apr 21
LettuceSow outdoors · Mar 31 – Apr 14
Carrots, beetsSow outdoors · Apr 7 – Apr 21
TomatoesStart indoors · Mar 3 – Mar 17
TomatoesTransplant · May 5 – May 19
Peppers, eggplantStart indoors · Feb 17 – Mar 3
Peppers, eggplantTransplant · May 12 – May 26
BeansSow outdoors · May 5 – May 19
Sweet cornSow outdoors · May 5 – May 19
Cucumbers, squashSow outdoors · May 5 – May 19
Fall lettuce, spinachSow outdoors · Aug 18 – Sep 1
GarlicPlant cloves · Sep 29 – Nov 3
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 28) and first fall frost (Oct 13) 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 60552 came on Mar 25 — 13 days earlier than the 1991–2020 average (Apr 7).

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.

Trees 77

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 102

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican holly40 ft · blooms mid spring · low shade tolerance · to −20 °F

Wildflowers & perennials 210

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °FAmerican pokeweed7 ft · blooms mid summer · low shade tolerance · to −33 °F

Grasses 173

American beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBailey's sedge2.1 ft · blooms late spring · low shade tolerance · to −33 °Fbeaked sedge4 ft · blooms late spring · low shade tolerance · to −38 °Fbeaked spikerush3 ft · blooms late spring · high shade tolerance · to −28 °F

Vines 7

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °Ftrumpet honeysuckle16 ft · blooms late summer · low shade tolerance · to −33 °F

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 Somonauk, IL.

Soil in Somonauk, IL

The soil mapped at the center of ZIP 60552 is Flanagan — 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%moderate
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classprime farmlandUSDA classification

Map unit: Flanagan 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 60552; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Somonauk, IL

Summer high84 °Faverage high, July
Winter low15 °Faverage low, January
Hot days16days a year at 90 °F or more
Freezing nights142nights a year at 32 °F or less
Growing degree days3,013base 50 °F — the season’s usable heat
Longest day15 h 12 mindaylight on June 21
Shortest day9 h 09 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation42.4 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 31 °F, low 15 °F 31°15° JanFebruary: average high 35 °F, low 18 °F 35°18° FebMarch: average high 48 °F, low 28 °F 48°28° MarApril: average high 60 °F, low 37 °F 60°37° AprMay: average high 72 °F, low 49 °F 72°49° MayJune: average high 81 °F, low 59 °F 81°59° JunJuly: average high 84 °F, low 62 °F 84°62° JulAugust: average high 82 °F, low 60 °F 82°60° AugSeptember: average high 76 °F, low 52 °F 76°52° SepOctober: average high 63 °F, low 41 °F 63°41° OctNovember: average high 48 °F, low 29 °F 48°29° NovDecember: average high 36 °F, low 21 °F 36°21° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 1.96 in precipitation 2.0 JanFebruary: 1.94 in precipitation 1.9 FebMarch: 2.47 in precipitation 2.5 MarApril: 4.17 in precipitation 4.2 AprMay: 5.74 in precipitation 5.7 MayJune: 5.01 in precipitation 5.0 JunJuly: 4.76 in precipitation 4.8 JulAugust: 4.14 in precipitation 4.1 AugSeptember: 3.55 in precipitation 3.5 SepOctober: 3.86 in precipitation 3.9 OctNovember: 2.72 in precipitation 2.7 NovDecember: 2.11 in precipitation 2.1 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Chicago Aurora Municipal Airport, IL (14 mi away); precipitation: Somonauk 1.9 Ne, IL (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

605485b
Sandwich, IL · 4 mi
605315b
Leland, IL · 5 mi
605565b
Waterman, IL · 7 mi
605205b
Hinckley, IL · 9 mi
605455b
Plano, IL · 9 mi
605375b
Millington, IL · 9 mi
605515b
Sheridan, IL · 10 mi
605115b
Big Rock, IL · 10 mi

Illinois planting zones →

Questions about 60552

What planting zone is ZIP code 60552?

ZIP code 60552 (Somonauk, 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 Somonauk, IL?

The median last spring frost (32 °F) near 60552 is April 28; after May 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Chicago Aurora Municipal Airport station.

When is the first frost in Somonauk, IL?

The median first fall frost near 60552 is October 13, giving a median frost-free growing season of 166 days.

When should I plant tomatoes in 60552?

Start tomato seeds indoors around Mar 3 – Mar 17 and set transplants outside around May 5 – May 19, one to three weeks after the median last frost.

How much rain and snow does 60552 get?

About 42.4 inches of precipitation a year (NOAA 1991–2020 normals, Somonauk 1.9 Ne station).

How hot do summers get in Somonauk, IL?

The average high peaks at 84 °F in July, with about 16 days a year at 90 °F or more.

What kind of soil does 60552 have?

The USDA soil survey maps Flanagan at the center of ZIP 60552: silt loam, somewhat poorly drained, pH about 6.2 (slightly acidic).

Did spring come early in Somonauk, IL in 2026?

Spring leaf-out near 60552 came on Mar 25 in 2026, 13 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Somonauk, IL?

Long-day onions: the longest day near 60552 is 15 h 12 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).