Philadelphia, Pennsylvania Frost Dates, Growing Season & Hardiness Zone

When is the last frost in Philadelphia?

In half of years, the last 32°F night has passed by Mar 30. In 1 year out of 10, one still comes after Apr 12. The last 36°F night (frost possible on plants) typically comes later, around Apr 8, and the last 28°F hard freeze earlier, around Mar 17.

There are 13 days between the typical date (Mar 30) and the safer 1-in-10 date (Apr 12). Planting in that stretch is a gamble, so keep an eye on the 10-day forecast.

The typical last 36°F night (frost possible on plants in low spots) comes around Apr 8, 9 days after the typical last 32°F night. On clear, calm nights, frost can form on leaves even when the thermometer reads above freezing.

Our station has the earliest typical last frost of the 16 eligible stations near Philadelphia. If your yard runs cool, lean toward the safer Apr 12 date.

Is it too early to plant in Philadelphia?

Before Mar 30 the odds of another 32°F night are better than even; after Apr 12 they are about 1 in 10 or less.

Today's risk is computed in your browser from the same NOAA probability table, shown as the range between the two nearest NOAA probability levels.

When is the first frost in Philadelphia?

The typical first fall freeze (32°F) comes by Nov 17, but 1 year in 10 it shows up as early as Nov 4. Cold 36°F nights (frost possible on plants) typically start around Nov 5, and the first hard freeze (28°F) typically comes around Nov 29.

To time a fall crop, count back from the typical first frost (Nov 17) or the safer Nov 4. The planting calendar works it out crop by crop.

How long is Philadelphia's growing season?

Philadelphia's frost-free season (32°F) typically runs 232 days. In about 1 year out of 10, it's shorter than 214 days.

A season this long fits most warm-season vegetables planted on time. Long-season crops do best when started from transplants.

Each year the station logs an average of 4,428 growing degree days (base 50°F), a measure of the heat available for crop growth.

How does Philadelphia's season compare?

Among the 56 U.S. cities with frost dates on this site, the typical frost-free season here is longer than in 36 of them and shorter than in 19.

Growing degree days (base 50°F)

Annual normal: 4,428 GDD (NOAA flag R, 22 years). Running total by the end of each month (sum of NOAA daily GDD normals, so the year-end total can differ slightly from the annual normal):

What growing zone is Philadelphia? (USDA 2023)

The 2023 USDA map puts Philadelphia in zone 7b (5 to 10°F average coldest winter night). On the 2012 map, most of the city was 7a. Comparing ZIPs listed in both tables, 28 of 49 moved up half a zone.

Zones: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 2026-10-08. Shown as published in the ZIP tables; this page does not show a zone map. Not the official USDA Plant Hardiness Zone Map (official map: planthardiness.ars.usda.gov).

Does the new zone change Philadelphia's frost dates?

No. A hardiness zone reflects only the average coldest winter temperature, not the timing of spring or fall frost. Philadelphia's frost dates come from NOAA's 1991–2020 frost probabilities, and the 2023 zone map didn't change them. Pick perennials that survive winter by zone; time your planting by frost dates.

Why do Philadelphia frost dates differ between websites?

If you've seen Apr 4 listed as Philadelphia's last frost date, that's the 30%-risk date: about 3 years in 10 still get a 32°F night after it. We lead with Mar 30, the 50% (median) date.

Apr 12 is the date we call 'safer': it's the 10%-risk date, with a 32°F night after it in only about 1 year in 10.

You may also see Apr 8. That's the 50% date for a 36°F night (frost possible on plants) rather than a 32°F freeze, so sites using 36°F as their cutoff list later dates.

Station choice is another reason dates differ. Our 16 qualifying stations within 25 miles of the city center range from Mar 30 to Apr 28 for the typical (50%) last 32°F frost (table below).

Which weather station is this based on?

Station

Philadelphia Franklin Institute (NOAA USC00366886, COOP)

Distance

4.1 mi SSW of the city center

Elevation

60 ft; city center 100 ft (USGS), difference −40 ft

Record

NOAA completeness flag S, 25 of 30 years (1991–2020)

Confidence

High (rule)

Confidence: High. At 4.1 miles from the city center and only 40 ft off in elevation, with frost statistics that meet our completeness rule (NOAA flag S, 25 of 30 years), this station is a close match.

Philadelphia planting dates at a glance

Balanced dates use the 30%-risk last-frost date as the anchor. The Philadelphia planting calendar has typical and safe dates, fall planting and a month-by-month list for 26 vegetables.

When to plant tomatoes in Philadelphia · Fall planting dates for Philadelphia

Frost dates near Philadelphia

All Pennsylvania cities

Frequently asked questions

What is the average last frost date in Philadelphia?

The typical (median, 50%) last 32°F night in Philadelphia is Mar 30, based on NOAA 1991–2020 normals at Philadelphia Franklin Institute. For a safer target, use Apr 12; after that, only about 1 year in 10 still has a freeze.

When is the first frost in Philadelphia?

Typically by Nov 17 for the first 32°F night, though about 1 year in 10 it comes as early as Nov 4. The first 36°F night (frost possible on plants) typically shows up around Nov 5.

What growing zone is Philadelphia, Pennsylvania?

On the current 2023 USDA map, Philadelphia is in hardiness zone 7b. Older references based on the 2012 map may say 7a, which covered most of the city then.

Is it too early to plant in Philadelphia?

If it's before Mar 30, it's too early for frost-tender plants: another 32°F night is more likely than not. From Mar 30 to Apr 12, the risk falls from 50% to 10%. Cool-season crops such as peas and lettuce can be planted weeks earlier (see the planting calendar).

What temperature is a killing frost?

A light frost is enough to kill tender crops such as tomatoes. CSU Extension describes 28–32°F as a light frost and anything below 28°F as a heavy frost. We report NOAA odds at three thresholds: 36°F (frost possible on plants), 32°F (freeze, our headline) and 28°F (hard freeze).

Is first frost the same as first freeze?

Not quite. A 'freeze' means the air reached 32°F. 'Frost' is ice on surfaces, and it can form on calm, clear nights even when the air is a few degrees above freezing. So in Philadelphia, the first 36°F night (frost possible on plants) typically comes around Nov 5, before the first 32°F night (Nov 17).

Download & sources

• Add Philadelphia frost & planting dates to your calendar (.ics, 2027)
• Printable planting calendar (PDF)
• How these numbers are calculated

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal and daily normals, station USC00366886); USDA Plant Hardiness Zone ZIP tables 2023 and 2012 by the PRISM Group, Oregon State University; Census 2020 ZIP/place relationship file; USGS elevation. Long-term odds, not a forecast. Figures and sentences are generated from these data by fixed rules; see the methodology. Last updated 2026-10-08.