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

Planting zone for West Mifflin, PA

West Mifflin, PA is in USDA zone 6b across its 2 ZIP codes. The median last spring frost is April 18 and the first fall frost October 28.

West Mifflin on the zone map

Outlined: its 2 ZIP code areas · 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
ZIP codes2
Last frostApr 18
First frostOct 28
Growing season193 days

6b 2 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for West Mifflin, 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 West Mifflin, PA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 18median — 50% chance of a later frost
Safe for tender plantsMay 6only 10% chance of frost after
First fall frostOctober 28median — 10% chance by Oct 14
Growing season193 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 5 and returns around November 8.

From the NOAA station Pittsburgh Allegheny Co. Airport, PA, elevation 1,247 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 West Mifflin

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 7 – Mar 21
SpinachSow outdoors · Mar 7 – Mar 28
Broccoli, cabbageStart indoors · Feb 7 – Feb 21
Broccoli, cabbageTransplant · Mar 28 – Apr 11
Onion setsPlant outdoors · Mar 21 – Apr 4
PotatoesPlant outdoors · Mar 28 – Apr 11
LettuceSow outdoors · Mar 21 – Apr 4
Carrots, beetsSow outdoors · Mar 28 – Apr 11
TomatoesStart indoors · Feb 21 – Mar 7
TomatoesTransplant · Apr 25 – May 9
Peppers, eggplantStart indoors · Feb 7 – Feb 21
Peppers, eggplantTransplant · May 2 – May 16
BeansSow outdoors · Apr 25 – May 9
Sweet cornSow outdoors · Apr 25 – May 9
Cucumbers, squashSow outdoors · Apr 25 – May 9
Fall lettuce, spinachSow outdoors · Sep 2 – Sep 16
GarlicPlant cloves · Oct 14 – Nov 18
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 18) and first fall frost (Oct 28) 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 15122 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 6b in Pennsylvania

605 plants native to the lower 48 states, recorded in Pennsylvania, and rated by the USDA to survive −5 °F or colder — the bottom of zone 6b. 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 122

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 209

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 °FAtlantic mannagrass3 ft · blooms summer · low shade tolerance · to −8 °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 °F

Vines 10

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 °Fgraybark grape50 ft · blooms late spring · medium shade tolerance · to −8 °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 West Mifflin, PA.

Soil in West Mifflin, PA

The soil mapped at the center of ZIP 15122 is Guernsey — silt loam, moderately well drained. Much of the area is built over (urban land); this is the natural soil underneath.

TextureSilt loama good balance for most vegetables
pH6.0slightly acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter2%moderate
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classNot prime farmlandUSDA classification

Map unit: Urban land-Guernsey complex, gently sloping.

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 15122; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in West Mifflin, PA

Summer high83 °Faverage high, July
Winter low22 °Faverage low, January
Hot days8days a year at 90 °F or more
Freezing nights106nights a year at 32 °F or less
Growing degree days3,286base 50 °F — the season’s usable heat
Longest day15 h 03 mindaylight on June 21
Shortest day9 h 17 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation41.3 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 37 °F, low 22 °F 37°22° JanFebruary: average high 40 °F, low 24 °F 40°24° FebMarch: average high 49 °F, low 31 °F 49°31° MarApril: average high 63 °F, low 42 °F 63°42° AprMay: average high 72 °F, low 52 °F 72°52° MayJune: average high 79 °F, low 60 °F 79°60° JunJuly: average high 83 °F, low 64 °F 83°64° JulAugust: average high 81 °F, low 63 °F 81°63° AugSeptember: average high 75 °F, low 56 °F 75°56° SepOctober: average high 63 °F, low 45 °F 63°45° OctNovember: average high 51 °F, low 35 °F 51°35° NovDecember: average high 41 °F, low 28 °F 41°28° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.08 in precipitation 3.1 JanFebruary: 2.57 in precipitation 2.6 FebMarch: 3.22 in precipitation 3.2 MarApril: 3.40 in precipitation 3.4 AprMay: 4.08 in precipitation 4.1 MayJune: 4.58 in precipitation 4.6 JunJuly: 3.93 in precipitation 3.9 JulAugust: 3.81 in precipitation 3.8 AugSeptember: 3.54 in precipitation 3.5 SepOctober: 3.06 in precipitation 3.1 OctNovember: 3.03 in precipitation 3.0 NovDecember: 3.04 in precipitation 3.0 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Pittsburgh Allegheny Co. Airport, PA (within 1 mile); precipitation: Pittsburgh Allegheny Co. Airport, PA (within 1 mile). Daylight is calculated from latitude.

ZIP codes in West Mifflin

151226b
−5 to 0 °F
151236b
−5 to 0 °F

Pennsylvania planting zones →

Questions about West Mifflin

What planting zone is West Mifflin, PA?

West Mifflin, PA is in USDA hardiness zone 6b on the 2023 map (6b: −5 to 0 °F).

When is the last frost in West Mifflin, PA?

The median last spring frost is April 18 and the median first fall frost is October 28 (NOAA 1991–2020 normals, Pittsburgh Allegheny Co. Airport station).

When can I plant a garden in West Mifflin, PA?

Cool-season crops like peas and spinach go in around Mar 7 – Mar 28; tomatoes, peppers, beans and squash after about Apr 25, once frost risk has passed.

What kind of onions grow in West Mifflin, PA?

Long-day onions: the longest day is 15 h 03 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

How much rain and snow does West Mifflin, PA get?

About 41.3 inches of precipitation a year (NOAA 1991–2020 normals).