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

Planting zone for 62351 — Mendon, IL

ZIP code 62351 (Mendon, Adams County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is April 14 and the first fall frost October 23.

Where ZIP 62351 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.

Zone6a−10 to −5 °F
Coldest night−23.3 to −20.6 °C
Last frostApr 14
First frostOct 23
2012 zone5b

Was 5b 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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Mendon, 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 Mendon, IL

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 14median — 50% chance of a later frost
Safe for tender plantsMay 1only 10% chance of frost after
First fall frostOctober 23median — 10% chance by Oct 10
Growing season191 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 4 and returns around November 1.

From the NOAA station Quincy Regional Airport, IL — 13 miles away, elevation 768 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 62351

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 3 – Mar 17
SpinachSow outdoors · Mar 3 – Mar 24
Broccoli, cabbageStart indoors · Feb 3 – Feb 17
Broccoli, cabbageTransplant · Mar 24 – Apr 7
Onion setsPlant outdoors · Mar 17 – Mar 31
PotatoesPlant outdoors · Mar 24 – Apr 7
LettuceSow outdoors · Mar 17 – Mar 31
Carrots, beetsSow outdoors · Mar 24 – Apr 7
TomatoesStart indoors · Feb 17 – Mar 3
TomatoesTransplant · Apr 21 – May 5
Peppers, eggplantStart indoors · Feb 3 – Feb 17
Peppers, eggplantTransplant · Apr 28 – May 12
BeansSow outdoors · Apr 21 – May 5
Sweet cornSow outdoors · Apr 21 – May 5
Cucumbers, squashSow outdoors · Apr 21 – May 5
Fall lettuce, spinachSow outdoors · Aug 28 – Sep 11
GarlicPlant cloves · Oct 9 – Nov 13
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 14) and first fall frost (Oct 23) 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 62351 came on Mar 10 — 16 days earlier than the 1991–2020 average (Mar 26).

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 6a in Illinois

610 plants native to the lower 48 states, recorded in Illinois, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Trees 78

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 220

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 178

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 9

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 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °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 Mendon, IL.

Soil in Mendon, IL

The soil mapped at the center of ZIP 62351 is Clarksdale — silt loam, somewhat poorly drained.

TextureSilt loama good balance for most vegetables
pH6.6neutral; most vegetables like 6.0–7.0
DrainageSomewhat poorly drainedconsider raised beds
Organic matter2.5%moderate
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classprime farmlandUSDA classification

Map unit: Clarksdale silt loam, 2 to 5 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 62351; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mendon, IL

Summer high86 °Faverage high, July
Winter low19 °Faverage low, January
Hot days24days a year at 90 °F or more
Freezing nights112nights a year at 32 °F or less
Growing degree days3,691base 50 °F — the season’s usable heat
Longest day15 h 02 mindaylight on June 21
Shortest day9 h 19 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation36.4 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 35 °F, low 19 °F 35°19° JanFebruary: average high 40 °F, low 23 °F 40°23° FebMarch: average high 52 °F, low 32 °F 52°32° MarApril: average high 64 °F, low 43 °F 64°43° AprMay: average high 73 °F, low 54 °F 73°54° MayJune: average high 82 °F, low 63 °F 82°63° JunJuly: average high 86 °F, low 67 °F 86°67° JulAugust: average high 85 °F, low 65 °F 85°65° AugSeptember: average high 78 °F, low 56 °F 78°56° SepOctober: average high 65 °F, low 45 °F 65°45° OctNovember: average high 51 °F, low 33 °F 51°33° NovDecember: average high 39 °F, low 24 °F 39°24° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 1.57 in precipitation 1.6 JanFebruary: 1.77 in precipitation 1.8 FebMarch: 2.29 in precipitation 2.3 MarApril: 3.98 in precipitation 4.0 AprMay: 4.55 in precipitation 4.5 MayJune: 4.50 in precipitation 4.5 JunJuly: 3.49 in precipitation 3.5 JulAugust: 3.93 in precipitation 3.9 AugSeptember: 3.09 in precipitation 3.1 SepOctober: 3.05 in precipitation 3.0 OctNovember: 2.41 in precipitation 2.4 NovDecember: 1.80 in precipitation 1.8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Quincy Regional Airport, IL (13 mi away); precipitation: Quincy Regional Airport, IL (13 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6a.

623496a
Loraine, IL · 6 mi
623596a
Paloma, IL · 6 mi
623766a
Ursa, IL · 7 mi
623256a
Coatsburg, IL · 7 mi
623486a
Lima, IL · 7 mi
623386a
Fowler, IL · 8 mi
623806a
West Point, IL · 10 mi
623736a
Sutter, IL · 10 mi

Illinois planting zones →

Questions about 62351

What planting zone is ZIP code 62351?

ZIP code 62351 (Mendon, IL) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Mendon, IL?

The median last spring frost (32 °F) near 62351 is April 14; after May 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Quincy Regional Airport station.

When is the first frost in Mendon, IL?

The median first fall frost near 62351 is October 23, giving a median frost-free growing season of 191 days.

When should I plant tomatoes in 62351?

Start tomato seeds indoors around Feb 17 – Mar 3 and set transplants outside around Apr 21 – May 5, one to three weeks after the median last frost.

How much rain and snow does 62351 get?

About 36.4 inches of precipitation a year (NOAA 1991–2020 normals, Quincy Regional Airport station).

How hot do summers get in Mendon, IL?

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 62351 have?

The USDA soil survey maps Clarksdale at the center of ZIP 62351: silt loam, somewhat poorly drained, pH about 6.6 (neutral).

Did spring come early in Mendon, IL in 2026?

Spring leaf-out near 62351 came on Mar 10 in 2026, 16 days earlier than the 1991–2020 average (Mar 26), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Mendon, IL?

Long-day onions: the longest day near 62351 is 15 h 02 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 62351 change?

Yes. The 2012 USDA map put 62351 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.