Last spring frost
Apr 7
Frost Dates for Mercersburg, PA
First fall frost
Nov 4
Growing season
209 days
Hardiness zone
7a
In an average year around Mercersburg, PA, the last spring frost (32°F) is about Apr 7 and the first fall frost is about Nov 4, giving roughly a 209-day growing season. To be safe most years, wait until Mar 25 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) | May 7 | Apr 19 | Apr 6 |
| Freeze (32°F) | Apr 21 | Apr 7 | Mar 25 |
| Hard (28°F) | Apr 8 | Mar 28 | Mar 13 |
| Severe (24°F) | Mar 31 | Mar 17 | Feb 28 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 7 | May 1 | Apr 26 | Apr 22 | Apr 19 | Apr 17 | Apr 14 | Apr 11 | Apr 6 |
| 32°F | Apr 21 | Apr 16 | Apr 12 | Apr 10 | Apr 7 | Apr 4 | Apr 2 | Mar 30 | Mar 25 |
| 28°F | Apr 8 | Apr 4 | Apr 2 | Mar 30 | Mar 28 | Mar 25 | Mar 22 | Mar 18 | Mar 13 |
| 24°F | Mar 31 | Mar 27 | Mar 23 | Mar 20 | Mar 17 | Mar 14 | Mar 11 | Mar 7 | Feb 28 |
| 20°F | Mar 22 | Mar 17 | Mar 13 | Mar 10 | Mar 7 | Mar 4 | Feb 28 | Feb 23 | Feb 14 |
| 16°F | Mar 14 | Mar 9 | Mar 5 | Mar 1 | Feb 27 | Feb 21 | Feb 13 | Feb 7 | Jan 30 |
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) | Oct 9 | Oct 23 | Nov 5 |
| Freeze (32°F) | Oct 22 | Nov 4 | Nov 17 |
| Hard (28°F) | Nov 1 | Nov 14 | Dec 2 |
| Severe (24°F) | Nov 11 | Nov 29 | Dec 17 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 9 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Oct 28 | Nov 1 | Nov 5 |
| 32°F | Oct 22 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 6 | Nov 8 | Nov 12 | Nov 17 |
| 28°F | Nov 1 | Nov 5 | Nov 9 | Nov 11 | Nov 14 | Nov 18 | Nov 22 | Nov 26 | Dec 2 |
| 24°F | Nov 11 | Nov 16 | Nov 20 | Nov 25 | Nov 29 | Dec 2 | Dec 6 | Dec 11 | Dec 17 |
| 20°F | Nov 24 | Dec 1 | Dec 5 | Dec 9 | Dec 14 | Dec 19 | Dec 22 | Dec 27 | Jan 2 |
| 16°F | Dec 8 | Dec 14 | Dec 21 | Dec 25 | Dec 28 | Jan 1 | Jan 6 | Jan 12 | Jan 20 |
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: Hagerstown Washington Co Ap, Md, about 13.2 miles away@if(!empty($station['elevation_ft'])), at 698 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 Mercersburg, PA?
On average, the last spring frost (32°F) around Mercersburg, PA is about Apr 7. In cooler years it can run later, so for a safer bet many gardeners wait until Mar 25.
When is the first frost in the fall?
The first fall frost around Mercersburg, PA typically arrives about Nov 4. 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 Apr 7 on average, or Mar 25 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 209 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 17236 Planting calendar → Pennsylvania frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026