Pennsylvania Planting Zones and Frost Dates by Town

Pennsylvania runs from USDA plant hardiness zone 5b in the northern tier to 8a along the Delaware River below Philadelphia, and its typical last spring frost runs from April 2 at Philadelphia to May 18 at Bradford. Most of central Pennsylvania, including Lock Haven, Williamsport and State College, is zone 6a or 6b, with a typical last frost in the second half of April and a first fall frost in the second half of October.

What planting zone am I in? Pennsylvania zones by town

USDA zones are based on the average coldest winter night of the year from 1991 to 2020. Each full zone spans 10°F and each “a” or “b” half spans 5°F (USDA). These are the 2023 zones for each town’s ZIP code, from the official map’s ZIP code data published by Oregon State University’s PRISM Climate Group, which produced the map with USDA.

Town (ZIP)	County	2023 zone	Average coldest night
Lock Haven (17745)	Clinton	6a	-10 to -5°F
Mill Hall (17751)	Clinton	6b	-5 to 0°F
Renovo (17764)	Clinton	6a	-10 to -5°F
Jersey Shore (17740)	Lycoming	6a	-10 to -5°F
Williamsport (17701)	Lycoming	6a	-10 to -5°F
Montoursville (17754)	Lycoming	6b	-5 to 0°F
Lewisburg (17837)	Union	6b	-5 to 0°F
Sunbury (17801)	Northumberland	6b	-5 to 0°F
State College (16801)	Centre	6b	-5 to 0°F
Bellefonte (16823)	Centre	6b	-5 to 0°F
Snow Shoe (16874)	Centre	6a	-10 to -5°F
Clearfield (16830)	Clearfield	6a	-10 to -5°F
Altoona (16601)	Blair	6b	-5 to 0°F
Wellsboro (16901)	Tioga	6a	-10 to -5°F
Coudersport (16915)	Potter	5b	-15 to -10°F
Bradford (16701)	McKean	5b	-15 to -10°F
Erie (16501)	Erie	7a	0 to 5°F
Pittsburgh (15222)	Allegheny	7a	0 to 5°F
Harrisburg (17101)	Dauphin	7a	0 to 5°F
Lancaster (17602)	Lancaster	7a	0 to 5°F
Allentown (18102)	Lehigh	7a	0 to 5°F
Scranton (18503)	Lackawanna	6b	-5 to 0°F
Wilkes-Barre (18702)	Luzerne	6a	-10 to -5°F
Philadelphia (19103)	Philadelphia	7b	5 to 10°F
Ridley Park (19078)	Delaware	8a	10 to 15°F

Most of Pennsylvania’s 5b ZIP codes are in the northern tier, from Warren and McKean counties east through Potter and Tioga to Wayne and Susquehanna counties. Only three ZIP codes, all along the Delaware River in Delaware County (Chester, Eddystone and Ridley Park), reach 8a. A ZIP code’s zone describes the area as a whole: Lock Haven’s ZIP is 6a while neighboring Mill Hall’s is 6b. USDA notes that low spots where cold air settles run colder than the map, and spots near pavement or a sheltered south wall run warmer.

What changed from the 2012 zone map

USDA released the current map on November 15, 2023. It uses 1991 to 2020 temperatures from 13,412 weather stations, up from 7,983 for the 2012 map. About half of the country moved into the next warmer half zone, and other areas warmed slightly without changing zones. USDA credits newer data, better mapping methods and the added stations, and cautions against reading the changes as a measure of climate change. If your zone changed, USDA says plants that are thriving will likely keep thriving; there’s no reason to pull them.

Using your zone to pick shrubs and trees

Nursery tags list the zones a plant is rated for. Choose plants rated for your zone, and be careful about “pushing” a zone with plants rated only for warmer ones. USDA’s guidance on using the map adds:

• The zone only measures winter cold. Light, soil moisture, humidity, wind, snow cover and soil type all affect whether a plant makes it.
• The map shows average lows, not record lows. A rare cold snap can still kill plants that have done well for years.
• Dry soil in late fall can injure plants that would otherwise be hardy, because they go into winter under moisture stress. Don’t let fall plantings go into winter dry.
• Low humidity makes cold injury worse, especially on evergreens, and strong winter sun can hurt shade plants at the edge of their range.
• An early fall cold snap, or a midwinter thaw followed by a hard freeze, can injure plants even when temperatures never reach the zone’s average low.

Hardy isn’t the same as legal. Some common landscape shrubs and trees, including Japanese barberry, burning bush and Callery pear, are on Pennsylvania’s noxious weed list and can’t be sold, transported or planted here. The Department’s list links approved exempt varieties for Japanese barberry; it shows none for the other two.

Pennsylvania frost dates by town

These are NOAA’s 1991 to 2020 climate normals for a low of 32°F at each weather station, sorted from earliest to latest last frost.

NOAA station	Typical last spring frost	Safer last frost (10%)	Early first frost (10%)	Typical first fall frost	Typical frost-free days
Philadelphia Intl. Airport	April 2	April 13	October 30	November 10	224
Harrisburg Capital City Airport	April 9	April 25	October 16	November 1	205
State College	April 20	May 6	October 10	October 26	187
Allentown Intl. Airport	April 20	May 6	October 8	October 24	184
Pittsburgh Intl. Airport	April 23	May 12	October 9	October 23	181
Wilkes-Barre Intl. Airport	April 23	May 10	October 4	October 20	178
Williamsport	April 24	May 11	October 6	October 23	180
Erie Intl. Airport	April 26	May 13	October 21	November 4	192
Lock Haven	April 30	May 15	October 5	October 20	173
Bradford Regional Airport	May 18	May 31	September 18	October 1	136

Lock Haven has the shortest typical frost-free season of the central Pennsylvania stations here, 173 days, two weeks shorter than State College’s 187. For frost dates, rain and snow in 70 Pennsylvania towns, see our Pennsylvania climate by town page.

What the 50% and 10% frost dates mean

NOAA’s typical last frost is the date after which the chance of a freezing night drops below 50 percent. That’s a coin flip: in about half of years, there’s still a 32°F night after it. The 10% date is when the chance drops below 1 in 10, which makes it the safer date for frost-tender plants. In fall it works in reverse: there’s only a 1-in-10 chance the first frost comes before the early date.

For Lock Haven, the typical last frost is April 30, but the safer date is May 15. In fall, the typical first frost is October 20, and in one year out of ten it comes before October 5. These numbers come from one thermometer at each station; a low yard or creek bottom where cold air pools can frost on nights the station doesn’t.

When to plant, seed and build around frost dates

• Vegetable transplants: Penn State Extension’s York County transplanting guide, built around a May 1 last frost, sets out cool-season crops like broccoli, cabbage and lettuce about 1 to 4 weeks before the last frost, and warm-season crops like tomatoes, peppers and squash starting about 10 days to 2 weeks after it. Shift those dates to your own town’s frost dates; our Pennsylvania planting calendar does it for you.
• Grass seed: Penn State calls late summer the best time to seed in most of Pennsylvania: late August and early September soils are warm and dry, and seedlings get the fall and the next spring to establish before summer heat. Mid to late spring is the second choice. Seed sown too late in fall germinates poorly once soils turn cold. See best grass seed for Pennsylvania.
• Sod: Can go down almost any time the ground isn’t frozen; spring, late summer and fall are best.
• Footings and hardscape: Frost dates also mark the return of freezing nights. The residential code doesn’t allow footings on frozen soil (IRC R403.1.4.1), so late-fall wall and patio work needs a plan to keep the base from freezing.

Sources

• USDA Agricultural Research Service: USDA unveils updated Plant Hardiness Zone Map (Nov. 15, 2023)
• USDA Plant Hardiness Zone Map: How to use the maps
• PRISM Climate Group, Oregon State University: 2023 USDA hardiness zones by ZIP code (CSV)
• NOAA NCEI: U.S. Climate Normals, 1991-2020, annual freeze probability dates for stations USW00013739, USW00014751, USC00368449, USW00014737, USW00094823, USW00014777, USW00014778, USW00014860, USC00365109 and USW00004751 (example query)
• NOAA Climate.gov: Average date of last spring freeze
• Penn State Extension: Lawn establishment
• Penn State Extension Master Gardeners, York County: Vegetable transplanting guide
• PA Department of Agriculture: Controlled plant and noxious weed lists

Last checked November 14, 2026.

Common questions

What planting zone is central Pennsylvania?

Mostly 6a and 6b on the 2023 USDA map. Lock Haven, Williamsport and Jersey Shore are 6a; State College, Bellefonte, Lewisburg and Mill Hall are 6b. The coldest northern-tier ZIP codes, such as Coudersport and Bradford, are 5b.

When is the last frost in central Pennsylvania?

At NOAA’s central Pennsylvania stations the typical last spring frost is April 20 at State College, April 24 at Williamsport and April 30 at Lock Haven. For a safer date with only a 1-in-10 chance of a later frost, use May 6, May 11 and May 15.

Did Pennsylvania’s planting zones change?

The USDA released a new map in November 2023 using 1991 to 2020 data and 13,412 weather stations, up from 7,983. About half of the country moved a half zone warmer. USDA says plants that are thriving don’t need to be replaced.

When should I seed grass in Pennsylvania?

Penn State Extension says late summer is the best time to seed in most of Pennsylvania, when soils are warm and dry and seedlings get the fall and spring to establish. Mid to late spring is the second choice.

See every Pennsylvania building, digging and contractor rule on our Pennsylvania guide. Related: Pennsylvania planting calendar by town, best grass seed for Pennsylvania and rain, snow and frost by town.