Last spring frost
May 21
Frost Dates for Grassflat, PA
First fall frost
Sep 27
Growing season
130 days
Hardiness zone
6a
In an average year around Grassflat, PA, the last spring frost (32°F) is about May 21 and the first fall frost is about Sep 27, giving roughly a 130-day growing season. To be safe most years, wait until Apr 30 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Jun 15 | May 31 | May 15 |
| Freeze (32°F) | Jun 1 | May 21 | Apr 30 |
| Hard (28°F) | May 27 | May 7 | Apr 21 |
| Severe (24°F) | May 16 | Apr 25 | Apr 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 15 | Jun 8 | Jun 5 | Jun 2 | May 31 | May 29 | May 26 | May 22 | May 15 |
| 32°F | Jun 1 | May 30 | May 27 | May 24 | May 21 | May 17 | May 12 | May 7 | Apr 30 |
| 28°F | May 27 | May 22 | May 17 | May 12 | May 7 | May 3 | Apr 30 | Apr 25 | Apr 21 |
| 24°F | May 16 | May 9 | May 4 | Apr 30 | Apr 25 | Apr 21 | Apr 17 | Apr 12 | Apr 7 |
| 20°F | May 3 | Apr 20 | Apr 15 | Apr 11 | Apr 8 | Apr 4 | Apr 2 | Mar 31 | Mar 26 |
| 16°F | Apr 8 | Apr 3 | Apr 1 | Mar 30 | Mar 28 | Mar 24 | Mar 21 | Mar 18 | Mar 13 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Aug 31 | Sep 15 | Oct 1 |
| Freeze (32°F) | Sep 12 | Sep 27 | Oct 13 |
| Hard (28°F) | Sep 22 | Oct 8 | Oct 30 |
| Severe (24°F) | Oct 3 | Oct 24 | Nov 9 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 31 | Sep 4 | Sep 8 | Sep 12 | Sep 15 | Sep 18 | Sep 22 | Sep 26 | Oct 1 |
| 32°F | Sep 12 | Sep 17 | Sep 21 | Sep 24 | Sep 27 | Sep 30 | Oct 3 | Oct 6 | Oct 13 |
| 28°F | Sep 22 | Sep 29 | Oct 2 | Oct 6 | Oct 8 | Oct 12 | Oct 16 | Oct 22 | Oct 30 |
| 24°F | Oct 3 | Oct 11 | Oct 16 | Oct 20 | Oct 24 | Oct 29 | Nov 1 | Nov 5 | Nov 9 |
| 20°F | Oct 22 | Oct 29 | Nov 2 | Nov 5 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 22 |
| 16°F | Nov 5 | Nov 10 | Nov 14 | Nov 17 | Nov 20 | Nov 23 | Nov 27 | Dec 1 | Dec 7 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Clarence, Pa, about 9.2 miles away@if(!empty($station['elevation_ft'])), at 1,390 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Grassflat, PA?
On average, the last spring frost (32°F) around Grassflat, PA is about May 21. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 30.
When is the first frost in the fall?
The first fall frost around Grassflat, PA typically arrives about Sep 27. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around May 21 on average, or Apr 30 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 130 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 16839 Planting calendar → Pennsylvania frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026