Pennsylvania Frost Dates & Growing Season Guide
Pennsylvania (PA) spans USDA hardiness zones 6a, 6b, 7a, with growing seasons ranging from 170 days in Scranton to 218 days in Philadelphia. The average growing season across the state is approximately 187 days.
Pennsylvania City Frost Dates
The table below shows the average last spring frost date, first fall frost date, growing season length, and USDA hardiness zone for each city. Click a city name for detailed planting calendars and zone information.
| City | Last Spring Frost | First Fall Frost | Growing Season | Zone | Min Temp |
|---|---|---|---|---|---|
| Philadelphia | April 1 | November 5 | 218 days | 7a | 0°F |
| Pittsburgh | April 20 | October 18 | 181 days | 6b | -5°F |
| Harrisburg | April 12 | October 22 | 193 days | 6b | -5°F |
| Erie | April 28 | October 18 | 173 days | 6a | -10°F |
| Scranton | April 25 | October 12 | 170 days | 6a | -10°F |
Planting Windows for Pennsylvania
Based on average frost dates, here are the recommended planting windows for each city. The indoor seed start date is approximately seven weeks before the last spring frost. Transplanting should occur about two weeks after the last frost. The last direct sow date for fall crops is ten weeks before the first fall frost.
| City | Start Seeds Indoors | Transplant After | Last Direct Sow |
|---|---|---|---|
| Philadelphia | February 12 | April 15 | August 27 |
| Pittsburgh | March 2 | May 4 | August 9 |
| Harrisburg | February 23 | April 26 | August 13 |
| Erie | March 10 | May 12 | August 9 |
| Scranton | March 7 | May 9 | August 3 |
Gardening in Pennsylvania
Pennsylvania spans from Philadelphia's zone 7a coastal warmth to Erie's zone 6a lake-effect climate, with mountainous interior regions dropping to zone 5b in some valleys. The southeastern corner around Philadelphia has the longest growing season at over 215 days and can grow figs and other marginally hardy plants. Pittsburgh and the western plateau have about 180 days and heavier clay soils. Pennsylvania's varied terrain creates countless microclimates that observant gardeners exploit. The state grows excellent apples, stone fruits, and grapes. Tomatoes, peppers, and sweet corn are summer garden anchors. Starting seeds indoors in March is standard for warm-season crops, with transplanting in mid-to-late May depending on location.
Understanding Pennsylvania's Hardiness Zones
Pennsylvania includes USDA hardiness zones 6a, 6b, 7a. These zones indicate the average annual extreme minimum winter temperature for each area, which determines which perennial plants, trees, and shrubs can survive winter without protection. When purchasing trees, shrubs, or perennial flowers, always check that the plant is rated for your hardiness zone or a lower (colder) zone number.
Tips for Using Pennsylvania Frost Dates
These frost dates represent long-term averages and should be treated as guidelines rather than guarantees. In any given year, the actual last spring frost or first fall frost may arrive one to three weeks earlier or later than the average. Factors that affect your specific location include elevation above the city center, proximity to water, slope direction, and whether you are in an urban or rural area. South-facing slopes and areas near large pavement or building masses tend to be warmer than surrounding open land. Low-lying valleys and exposed hilltops are often colder than mid-slope positions.
To protect against late spring frosts, keep row cover fabric, old bed sheets, or frost blankets on hand. Monitor your local weather forecast daily as the average frost date approaches. When frost is predicted after you have transplanted, covering plants in the late afternoon traps ground heat and can protect against temperatures down to about 28 degrees Fahrenheit. For fall season extension, the same covers protect mature plants from early frosts, often buying several additional weeks of harvest.