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

Planting zone for 16839 — Grassflat, PA

ZIP code 16839 (Grassflat, Clearfield County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 21 and the first fall frost September 27.

Where ZIP 16839 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 21
First frostSep 27
2012 zone6a

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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Grassflat, 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 Grassflat, PA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 21median — 50% chance of a later frost
Safe for tender plantsJune 1only 10% chance of frost after
First fall frostSeptember 27median — 10% chance by Sep 12
Growing season130 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 7 and returns around October 8.

From the NOAA station Clarence, PA — 9 miles away, elevation 1,391 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 16839

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 9 – Apr 23
SpinachSow outdoors · Apr 9 – Apr 30
Broccoli, cabbageStart indoors · Mar 12 – Mar 26
Broccoli, cabbageTransplant · Apr 30 – May 14
Onion setsPlant outdoors · Apr 23 – May 7
PotatoesPlant outdoors · Apr 30 – May 14
LettuceSow outdoors · Apr 23 – May 7
Carrots, beetsSow outdoors · Apr 30 – May 14
TomatoesStart indoors · Mar 26 – Apr 9
TomatoesTransplant · May 28 – Jun 11
Peppers, eggplantStart indoors · Mar 12 – Mar 26
Peppers, eggplantTransplant · Jun 4 – Jun 18
BeansSow outdoors · May 28 – Jun 11
Sweet cornSow outdoors · May 28 – Jun 11
Cucumbers, squashSow outdoors · May 28 – Jun 11
Fall lettuce, spinachSow outdoors · Aug 2 – Aug 16
GarlicPlant cloves · Sep 13 – Oct 18
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 21) and first fall frost (Sep 27) 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 16839 came on Mar 31 — 9 days earlier than the 1991–2020 average (Apr 9).

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 Grassflat, PA.

Soil in Grassflat, PA

The soil mapped at the center of ZIP 16839 is Ernest — moderately decomposed plant material, moderately well drained.

TextureModerately decomposed plant materialtop layer
pH4.5strongly acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter60%high
Hydrologic groupDwater soaks in very slowly
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Ernest silt loam, 3 to 8 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 16839; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Grassflat, PA

Summer high82 °Faverage high, July
Winter low14 °Faverage low, January
Hot days6days a year at 90 °F or more
Freezing nights175nights a year at 32 °F or less
Growing degree days2,104base 50 °F — the season’s usable heat
Longest day15 h 08 mindaylight on June 21
Shortest day9 h 13 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation44.5 inper year, rain and melted snow
Snowfall50 inper year; 70 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 33 °F, low 14 °F 33°14° JanFebruary: average high 37 °F, low 14 °F 37°14° FebMarch: average high 46 °F, low 21 °F 46°21° MarApril: average high 59 °F, low 31 °F 59°31° AprMay: average high 70 °F, low 40 °F 70°40° MayJune: average high 78 °F, low 50 °F 78°50° JunJuly: average high 82 °F, low 53 °F 82°53° JulAugust: average high 81 °F, low 52 °F 81°52° AugSeptember: average high 74 °F, low 44 °F 74°44° SepOctober: average high 62 °F, low 35 °F 62°35° OctNovember: average high 49 °F, low 26 °F 49°26° NovDecember: average high 38 °F, low 21 °F 38°21° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″January: 3.17 in precipitation, 12.8 in snowfall 3.2❄13 JanFebruary: 2.56 in precipitation, 11.5 in snowfall 2.6❄12 FebMarch: 3.62 in precipitation, 11.4 in snowfall 3.6❄11 MarApril: 3.78 in precipitation, 1.7 in snowfall 3.8❄2 AprMay: 4.13 in precipitation 4.1 MayJune: 4.15 in precipitation 4.2 JunJuly: 3.97 in precipitation 4.0 JulAugust: 4.07 in precipitation 4.1 AugSeptember: 4.45 in precipitation 4.5 SepOctober: 3.80 in precipitation, 0.8 in snowfall 3.8❄1 OctNovember: 3.31 in precipitation, 3.1 in snowfall 3.3❄3 NovDecember: 3.46 in precipitation, 9 in snowfall 3.5❄9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Clarence, PA (9 mi away); precipitation: Clarence, PA (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6a.

168496a
Lanse, PA · 3 mi
168476a
Kylertown, PA · 3 mi
168796a
Winburne, PA · 3 mi
168346a
Drifting, PA · 3 mi
168596a
Moshannon, PA · 5 mi
168586a
Morrisdale, PA · 5 mi
168216a
Allport, PA · 6 mi
168606a
Munson, PA · 6 mi

Pennsylvania planting zones →

Questions about 16839

What planting zone is ZIP code 16839?

ZIP code 16839 (Grassflat, 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 Grassflat, PA?

The median last spring frost (32 °F) near 16839 is May 21; after June 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Clarence station.

When is the first frost in Grassflat, PA?

The median first fall frost near 16839 is September 27, giving a median frost-free growing season of 130 days.

When should I plant tomatoes in 16839?

Start tomato seeds indoors around Mar 26 – Apr 9 and set transplants outside around May 28 – Jun 11, one to three weeks after the median last frost.

How much rain and snow does 16839 get?

About 44.5 inches of precipitation a year and 50 inches of snowfall (NOAA 1991–2020 normals, Clarence station).

How hot do summers get in Grassflat, PA?

The average high peaks at 82 °F in July, with about 6 days a year at 90 °F or more.

What kind of soil does 16839 have?

The USDA soil survey maps Ernest at the center of ZIP 16839: moderately decomposed plant material, moderately well drained, pH about 4.5 (strongly acidic).

Did spring come early in Grassflat, PA in 2026?

Spring leaf-out near 16839 came on Mar 31 in 2026, 9 days earlier than the 1991–2020 average (Apr 9), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Grassflat, PA?

Long-day onions: the longest day near 16839 is 15 h 08 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).