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

Planting zone for 19373 — Thornton, PA

ZIP code 19373 (Thornton, Delaware County) is in USDA zone 7a: the coldest winter night averages 0 to 5 °F. The median last spring frost is April 26 and the first fall frost October 18.

Where ZIP 19373 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.

Zone7a0 to 5 °F

Coldest night−17.8 to −15 °C

Last frostApr 26

First frostOct 18

2012 zone7a

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 7a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Thornton, 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 Thornton, PA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 26median — 50% chance of a later frost

Safe for tender plantsMay 11only 10% chance of frost after

First fall frostOctober 18median — 10% chance by Oct 4

Growing season174 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 11 and returns around October 30.

From the NOAA station W Chester 2 Nw, PA — 7 miles away, elevation 374 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 19373

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 15 – Mar 29

SpinachSow outdoors · Mar 15 – Apr 5

Broccoli, cabbageStart indoors · Feb 15 – Mar 1

Broccoli, cabbageTransplant · Apr 5 – Apr 19

Onion setsPlant outdoors · Mar 29 – Apr 12

PotatoesPlant outdoors · Apr 5 – Apr 19

LettuceSow outdoors · Mar 29 – Apr 12

Carrots, beetsSow outdoors · Apr 5 – Apr 19

TomatoesStart indoors · Mar 1 – Mar 15

TomatoesTransplant · May 3 – May 17

Peppers, eggplantStart indoors · Feb 15 – Mar 1

Peppers, eggplantTransplant · May 10 – May 24

BeansSow outdoors · May 3 – May 17

Sweet cornSow outdoors · May 3 – May 17

Cucumbers, squashSow outdoors · May 3 – May 17

Fall lettuce, spinachSow outdoors · Aug 23 – Sep 6

GarlicPlant cloves · Oct 4 – Nov 8

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 26) and first fall frost (Oct 18) 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 19373 came on Mar 24 — about the same time as the 1991–2020 average (Mar 25).

average
Mar 252026
Mar 24

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 7a in Pennsylvania

620 plants native to the lower 48 states, recorded in Pennsylvania, and rated by the USDA to survive 0 °F or colder — the bottom of zone 7a. 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 Thornton, PA.

Soil in Thornton, PA

The soil mapped at the center of ZIP 19373 is Gladstone — gravelly loam, well drained.

TextureGravelly loama good balance for most vegetables

pH6.3slightly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3%moderate

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Gladstone gravelly loam, 15 to 25 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 19373; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Thornton, PA

Summer high86 °Faverage high, July

Winter low20 °Faverage low, January

Hot days27days a year at 90 °F or more

Freezing nights131nights a year at 32 °F or less

Growing degree days3,270base 50 °F — the season’s usable heat

Longest day15 h 00 mindaylight on June 21

Shortest day9 h 20 mindaylight on December 21

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

Precipitation48.7 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: W Chester 2 Nw, PA (7 mi away); precipitation: West Chester 2.4 Sse, PA (4 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.

193407a

Concordville, PA · 1 mi

193317a

Concordville, PA · 2 mi

193427a

Glen Mills, PA · 2 mi

Chester Heights, PA · 4 mi

190607b

Garnet Valley, PA · 4 mi

190397b

Gradyville, PA · 4 mi

Pennsylvania planting zones →

Questions about 19373

What planting zone is ZIP code 19373?

ZIP code 19373 (Thornton, PA) is in USDA hardiness zone 7a on the 2023 map: the coldest night of an average winter reaches 0 to 5 °F (−17.8 to −15 °C).

When is the last frost in Thornton, PA?

The median last spring frost (32 °F) near 19373 is April 26; after May 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, W Chester 2 Nw station.

When is the first frost in Thornton, PA?

The median first fall frost near 19373 is October 18, giving a median frost-free growing season of 174 days.

When should I plant tomatoes in 19373?

Start tomato seeds indoors around Mar 1 – Mar 15 and set transplants outside around May 3 – May 17, one to three weeks after the median last frost.

How much rain and snow does 19373 get?

About 48.7 inches of precipitation a year (NOAA 1991–2020 normals, West Chester 2.4 Sse station).

How hot do summers get in Thornton, PA?

The average high peaks at 86 °F in July, with about 27 days a year at 90 °F or more.

What kind of soil does 19373 have?

The USDA soil survey maps Gladstone at the center of ZIP 19373: gravelly loam, well drained, pH about 6.3 (slightly acidic).

Did spring come early in Thornton, PA in 2026?

Spring leaf-out near 19373 came on Mar 24 in 2026, about the same as the 1991–2020 average (Mar 25), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Thornton, PA?

Long-day onions: the longest day near 19373 is 15 h 00 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).