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

Planting zone for 18421 — Forest City, PA

ZIP code 18421 (Forest City, Susquehanna County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 14 and the first fall frost October 1.

Where ZIP 18421 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 frostMay 14
First frostOct 1
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 Forest City, PA…

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 Forest City, PA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 14median — 50% chance of a later frost
Safe for tender plantsMay 29only 10% chance of frost after
First fall frostOctober 1median — 10% chance by Sep 21
Growing season140 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 3 and returns around October 12.

From the NOAA station Pleasant Mt 1 W, PA — 6 miles away, elevation 1,801 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 18421

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 2 – Apr 16
SpinachSow outdoors · Apr 2 – Apr 23
Broccoli, cabbageStart indoors · Mar 5 – Mar 19
Broccoli, cabbageTransplant · Apr 23 – May 7
Onion setsPlant outdoors · Apr 16 – Apr 30
PotatoesPlant outdoors · Apr 23 – May 7
LettuceSow outdoors · Apr 16 – Apr 30
Carrots, beetsSow outdoors · Apr 23 – May 7
TomatoesStart indoors · Mar 19 – Apr 2
TomatoesTransplant · May 21 – Jun 4
Peppers, eggplantStart indoors · Mar 5 – Mar 19
Peppers, eggplantTransplant · May 28 – Jun 11
BeansSow outdoors · May 21 – Jun 4
Sweet cornSow outdoors · May 21 – Jun 4
Cucumbers, squashSow outdoors · May 21 – Jun 4
Fall lettuce, spinachSow outdoors · Aug 6 – Aug 20
GarlicPlant cloves · Sep 17 – Oct 22
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 14) and first fall frost (Oct 1) 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 18421 came on Apr 9 — 10 days earlier than the 1991–2020 average (Apr 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 6a in Pennsylvania

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

Trees 76

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 121

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 207

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 170

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 spikerush3 ft · blooms late spring · high shade tolerance · to −28 °FBebb's sedge3 ft · blooms late spring · low shade tolerance · to −38 °F

Vines 9

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 creeper2 ft · blooms summer · high shade tolerance · to −13 °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 Forest City, PA.

Soil in Forest City, PA

The soil mapped at the center of ZIP 18421 is Lordstown — moderately decomposed plant material, well drained.

TextureModerately decomposed plant materialtop layer
pH4.8strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter80%high
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Lordstown, Oquaga, and Cadosia soils, 15 to 25 percent slopes, extremely bouldery.

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 18421; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Forest City, PA

Summer high77 °Faverage high, July
Winter low12 °Faverage low, January
Hot days1days a year at 90 °F or more
Freezing nights169nights a year at 32 °F or less
Growing degree days1,887base 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)
Precipitation45.3 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 29 °F, low 12 °F 29°12° JanFebruary: average high 32 °F, low 13 °F 32°13° FebMarch: average high 40 °F, low 20 °F 40°20° MarApril: average high 53 °F, low 31 °F 53°31° AprMay: average high 65 °F, low 43 °F 65°43° MayJune: average high 73 °F, low 52 °F 73°52° JunJuly: average high 77 °F, low 56 °F 77°56° JulAugust: average high 76 °F, low 55 °F 76°55° AugSeptember: average high 69 °F, low 47 °F 69°47° SepOctober: average high 57 °F, low 36 °F 57°36° OctNovember: average high 45 °F, low 27 °F 45°27° NovDecember: average high 34 °F, low 19 °F 34°19° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.32 in precipitation 3.3 JanFebruary: 2.83 in precipitation 2.8 FebMarch: 3.26 in precipitation 3.3 MarApril: 3.74 in precipitation 3.7 AprMay: 3.91 in precipitation 3.9 MayJune: 4.52 in precipitation 4.5 JunJuly: 4.52 in precipitation 4.5 JulAugust: 4.32 in precipitation 4.3 AugSeptember: 4.23 in precipitation 4.2 SepOctober: 4.37 in precipitation 4.4 OctNovember: 3.05 in precipitation 3.0 NovDecember: 3.23 in precipitation 3.2 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Pleasant Mt 1 W, PA (6 mi away); precipitation: Forest City 0.2 Se, PA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

3 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

184136a
Clifford, PA · 2 mi
184705b
Union Dale, PA · 5 mi
184305b
Herrick Center, PA · 5 mi
184076a
Carbondale, PA · 5 mi
184416a
Lenoxville, PA · 7 mi
184726a
Waymart, PA · 7 mi
184336a
Jermyn, PA · 8 mi
184535b
Pleasant Mount, PA · 9 mi

Pennsylvania planting zones →

Questions about 18421

What planting zone is ZIP code 18421?

ZIP code 18421 (Forest City, PA) 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 Forest City, PA?

The median last spring frost (32 °F) near 18421 is May 14; after May 29 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Pleasant Mt 1 W station.

When is the first frost in Forest City, PA?

The median first fall frost near 18421 is October 1, giving a median frost-free growing season of 140 days.

When should I plant tomatoes in 18421?

Start tomato seeds indoors around Mar 19 – Apr 2 and set transplants outside around May 21 – Jun 4, one to three weeks after the median last frost.

How much rain and snow does 18421 get?

About 45.3 inches of precipitation a year (NOAA 1991–2020 normals, Forest City 0.2 Se station).

How hot do summers get in Forest City, PA?

The average high peaks at 77 °F in July, with about 1 days a year at 90 °F or more.

What kind of soil does 18421 have?

The USDA soil survey maps Lordstown at the center of ZIP 18421: moderately decomposed plant material, well drained, pH about 4.8 (strongly acidic).

Did spring come early in Forest City, PA in 2026?

Spring leaf-out near 18421 came on Apr 9 in 2026, 10 days earlier than the 1991–2020 average (Apr 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Forest City, PA?

Long-day onions: the longest day near 18421 is 15 h 12 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 18421 change?

Yes. The 2012 USDA map put 18421 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.