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

Planting zone for 62427 — Flat Rock, IL

ZIP code 62427 (Flat Rock, Crawford County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is April 8 and the first fall frost October 26.

Where ZIP 62427 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 8
First frostOct 26
2012 zone6a

Was 6a 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 6b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Flat Rock, 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 Flat Rock, IL

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 8median — 50% chance of a later frost
Safe for tender plantsApril 22only 10% chance of frost after
First fall frostOctober 26median — 10% chance by Oct 13
Growing season200 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 29 and returns around November 5.

From the NOAA station Lawrenceville Intl Airport, IL — 8 miles away, elevation 430 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 62427

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Feb 25 – Mar 11
SpinachSow outdoors · Feb 25 – Mar 18
Broccoli, cabbageStart indoors · Jan 28 – Feb 11
Broccoli, cabbageTransplant · Mar 18 – Apr 1
Onion setsPlant outdoors · Mar 11 – Mar 25
PotatoesPlant outdoors · Mar 18 – Apr 1
LettuceSow outdoors · Mar 11 – Mar 25
Carrots, beetsSow outdoors · Mar 18 – Apr 1
TomatoesStart indoors · Feb 11 – Feb 25
TomatoesTransplant · Apr 15 – Apr 29
Peppers, eggplantStart indoors · Jan 28 – Feb 11
Peppers, eggplantTransplant · Apr 22 – May 6
BeansSow outdoors · Apr 15 – Apr 29
Sweet cornSow outdoors · Apr 15 – Apr 29
Cucumbers, squashSow outdoors · Apr 15 – Apr 29
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 8) 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 62427 came on Mar 8 — 11 days earlier than the 1991–2020 average (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 6b in Illinois

620 plants native to the lower 48 states, recorded in Illinois, and rated by the USDA to survive −5 °F or colder — the bottom of zone 6b. Each links to its USDA PLANTS profile.

Trees 80

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 108

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 222

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 182

American beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fautumn bluegrass1.5 ft · blooms late spring · medium shade tolerance · to −8 °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 °F

Vines 11

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fcatbird grape30 ft · blooms late spring · medium shade tolerance · to −13 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °Fgraybark grape50 ft · blooms late spring · medium shade tolerance · to −8 °Fheartleaf peppervine2 ft · blooms late spring · low shade tolerance · to −8 °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 Flat Rock, IL.

Soil in Flat Rock, IL

The soil mapped at the center of ZIP 62427 is Wakeland — 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 matter2%moderate
Hydrologic groupB/Dmoderate when drained; wet otherwise
Farmland classPrime farmland if drained and either protected from flooding or not frequently flooded during the growing seasonUSDA classification

Map unit: Wakeland silt loam, 0 to 2 percent slopes, frequently 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 62427; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Flat Rock, IL

Summer high88 °Faverage high, July
Winter low23 °Faverage low, January
Hot days41days a year at 90 °F or more
Freezing nights97nights a year at 32 °F or less
Growing degree days4,131base 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
Precipitation41.7 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 39 °F, low 23 °F 39°23° JanFebruary: average high 44 °F, low 27 °F 44°27° FebMarch: average high 55 °F, low 35 °F 55°35° MarApril: average high 67 °F, low 45 °F 67°45° AprMay: average high 77 °F, low 56 °F 77°56° MayJune: average high 85 °F, low 64 °F 85°64° JunJuly: average high 88 °F, low 67 °F 88°67° JulAugust: average high 87 °F, low 65 °F 87°65° AugSeptember: average high 82 °F, low 57 °F 82°57° SepOctober: average high 69 °F, low 46 °F 69°46° OctNovember: average high 55 °F, low 35 °F 55°35° NovDecember: average high 43 °F, low 27 °F 43°27° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.16 in precipitation 3.2 JanFebruary: 2.16 in precipitation 2.2 FebMarch: 3.16 in precipitation 3.2 MarApril: 4.24 in precipitation 4.2 AprMay: 4.85 in precipitation 4.8 MayJune: 4.38 in precipitation 4.4 JunJuly: 4.22 in precipitation 4.2 JulAugust: 2.94 in precipitation 2.9 AugSeptember: 2.94 in precipitation 2.9 SepOctober: 3.51 in precipitation 3.5 OctNovember: 3.44 in precipitation 3.4 NovDecember: 2.66 in precipitation 2.7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Lawrenceville Intl Airport, IL (8 mi away); precipitation: Lawrenceville Intl Airport, IL (8 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6b.

624516b
Palestine, IL · 7 mi
624396b
Lawrenceville, IL · 9 mi
624546b
Robinson, IL · 10 mi
475616b
Oaktown, IN · 11 mi
624646b
Stoy, IL · 13 mi
624176b
Bridgeport, IL · 13 mi
475166b
Bruceville, IN · 14 mi
478616b
Merom, IN · 14 mi

Illinois planting zones →

Questions about 62427

What planting zone is ZIP code 62427?

ZIP code 62427 (Flat Rock, IL) 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 Flat Rock, IL?

The median last spring frost (32 °F) near 62427 is April 8; after April 22 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Lawrenceville Intl Airport station.

When is the first frost in Flat Rock, IL?

The median first fall frost near 62427 is October 26, giving a median frost-free growing season of 200 days.

When should I plant tomatoes in 62427?

Start tomato seeds indoors around Feb 11 – Feb 25 and set transplants outside around Apr 15 – Apr 29, one to three weeks after the median last frost.

How much rain and snow does 62427 get?

About 41.7 inches of precipitation a year (NOAA 1991–2020 normals, Lawrenceville Intl Airport station).

How hot do summers get in Flat Rock, IL?

The average high peaks at 88 °F in July, with about 41 days a year at 90 °F or more.

What kind of soil does 62427 have?

The USDA soil survey maps Wakeland at the center of ZIP 62427: silt loam, somewhat poorly drained, pH about 6.2 (slightly acidic).

Did spring come early in Flat Rock, IL in 2026?

Spring leaf-out near 62427 came on Mar 8 in 2026, 11 days earlier than the 1991–2020 average (Mar 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Flat Rock, IL?

Intermediate onions: the longest day near 62427 is 14 h 54 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 62427 change?

Yes. The 2012 USDA map put 62427 in zone 6a; the 2023 map puts it in zone 6b. The newer map uses 1991–2020 data and more weather stations.