Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 16346 — Seneca, PA

ZIP code 16346 (Seneca, Venango County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 2 and the first fall frost October 23.

Where ZIP 16346 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 2

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 Seneca, 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 Seneca, PA

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMay 2median — 50% chance of a later frost

Safe for tender plantsMay 20only 10% chance of frost after

First fall frostOctober 23median — 10% chance by Oct 8

Growing season171 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 21 and returns around November 3.

From the NOAA station Franklin, PA — 8 miles away, elevation 1,014 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 16346

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 21 – Apr 4

SpinachSow outdoors · Mar 21 – Apr 11

Broccoli, cabbageStart indoors · Feb 21 – Mar 7

Broccoli, cabbageTransplant · Apr 11 – Apr 25

Onion setsPlant outdoors · Apr 4 – Apr 18

PotatoesPlant outdoors · Apr 11 – Apr 25

LettuceSow outdoors · Apr 4 – Apr 18

Carrots, beetsSow outdoors · Apr 11 – Apr 25

TomatoesStart indoors · Mar 7 – Mar 21

TomatoesTransplant · May 9 – May 23

Peppers, eggplantStart indoors · Feb 21 – Mar 7

Peppers, eggplantTransplant · May 16 – May 30

BeansSow outdoors · May 9 – May 23

Sweet cornSow outdoors · May 9 – May 23

Cucumbers, squashSow outdoors · May 9 – May 23

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 (May 2) 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 16346 came on Mar 25 — 14 days earlier than the 1991–2020 average (Apr 8).

average
Apr 82026
Mar 25

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.

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 Seneca, PA.

Soil in Seneca, PA

The soil mapped at the center of ZIP 16346 is Brinkerton — slightly decomposed plant material, poorly drained.

TextureSlightly decomposed plant materialtop layer

pH4.5strongly acidic; most vegetables like 6.0–7.0

DrainagePoorly drainedconsider raised beds

Organic matter69%high

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Brinkerton and Frenchtown silt loams, 0 to 8 percent slopes, extremely stony.

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 16346; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Seneca, PA

Summer high83 °Faverage high, July

Winter low18 °Faverage low, January

Hot days10days a year at 90 °F or more

Freezing nights142nights a year at 32 °F or less

Growing degree days2,697base 50 °F — the season’s usable heat

Longest day15 h 10 mindaylight on June 21

Shortest day9 h 11 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation46.3 inper year, rain and melted snow

Snowfall54 inper year; 56 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

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

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6a.

Rouseville, PA · 6 mi

Kennerdell, PA · 11 mi

Pennsylvania planting zones →

Questions about 16346

What planting zone is ZIP code 16346?

ZIP code 16346 (Seneca, 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 Seneca, PA?

The median last spring frost (32 °F) near 16346 is May 2; after May 20 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Franklin station.

When is the first frost in Seneca, PA?

The median first fall frost near 16346 is October 23, giving a median frost-free growing season of 171 days.

When should I plant tomatoes in 16346?

Start tomato seeds indoors around Mar 7 – Mar 21 and set transplants outside around May 9 – May 23, one to three weeks after the median last frost.

How much rain and snow does 16346 get?

About 46.3 inches of precipitation a year and 54 inches of snowfall (NOAA 1991–2020 normals, Franklin station).

How hot do summers get in Seneca, PA?

The average high peaks at 83 °F in July, with about 10 days a year at 90 °F or more.

What kind of soil does 16346 have?

The USDA soil survey maps Brinkerton at the center of ZIP 16346: slightly decomposed plant material, poorly drained, pH about 4.5 (strongly acidic).

Did spring come early in Seneca, PA in 2026?

Spring leaf-out near 16346 came on Mar 25 in 2026, 14 days earlier than the 1991–2020 average (Apr 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Seneca, PA?

Long-day onions: the longest day near 16346 is 15 h 10 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 16346 change?

Yes. The 2012 USDA map put 16346 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.