Frost dates for 19373Thornton, PA
The average last spring frost in Thornton is April 26 and the average first fall frost is October 18, giving a typical growing season of about 174 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 26
- Average first fall frost
- Oct 18
- Growing season
- 174 days
Safer after May 11 (1-in-10 risk)
Possible by Oct 4 (1-in-10 risk)
Last frost typically in 174 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 23 · May 7 · May 22 | Sep 27 · Oct 7 · Oct 22 | 152 days | 100% |
| Frost / freeze (32°F) | Apr 10 · Apr 26 · May 11 | Oct 4 · Oct 18 · Nov 1 | 174 days | 100% |
| Hard freeze (28°F) | Mar 28 · Apr 11 · Apr 26 | Oct 14 · Oct 30 · Nov 11 | 198 days | 100% |
Planting calendar for Thornton
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Mar 26 – Jun 1 |
| Tomatoes | Transplant outdoors | May 12 – Jun 28 |
| Peppers | Start seeds indoors | Mar 26 – Apr 26 |
| Peppers | Transplant outdoors | May 26 – Jun 26 |
| Eggplant | Start seeds indoors | Apr 12 – May 11 |
| Eggplant | Transplant outdoors | May 26 – Jun 26 |
| Cucumbers | Sow outdoors | May 26 – Jul 8 |
| Summer squash | Sow outdoors | May 12 – Jun 26 |
| Winter squash & pumpkins | Sow outdoors | May 26 – Jun 26 |
| Snap beans | Sow outdoors | May 12 – Jul 31 |
| Sweet corn | Sow outdoors | May 12 – Jun 28 |
| Watermelon & cantaloupe | Sow outdoors | May 26 – Jun 26 |
| Okra | Sow outdoors | May 19 – Jun 11 |
| Peas | Sow outdoors (spring) | Mar 26 – May 11 |
| Potatoes | Plant outdoors (spring) | Mar 26 – May 26 |
| Onions | Start seeds indoors (spring) | Feb 12 – Mar 11 |
| Onions | Transplant outdoors (spring) | Apr 12 – May 11 |
| Broccoli | Start seeds indoors (spring) | Mar 8 – Apr 11 |
| Broccoli | Transplant outdoors (spring) | Apr 12 – May 11 |
| Broccoli | Start seeds indoors (fall) | Jun 18 – Jun 28 |
| Broccoli | Transplant outdoors (fall) | Jul 18 – Jul 29 |
| Cabbage | Start seeds indoors (spring) | Feb 26 – Mar 26 |
| Cabbage | Transplant outdoors (spring) | Mar 26 – Apr 26 |
| Cabbage | Start seeds indoors (fall) | Jun 8 – Jul 8 |
| Cabbage | Transplant outdoors (fall) | Jul 8 – Aug 8 |
| Leaf lettuce | Sow outdoors (spring) | Mar 26 – Jun 11 |
| Leaf lettuce | Sow outdoors (fall) | Jul 8 – Aug 24 |
| Spinach | Sow outdoors (spring) | Mar 19 – May 2 |
| Spinach | Sow outdoors (fall) | Jul 25 – Aug 29 |
| Radishes | Sow outdoors (spring) | Mar 26 – May 16 |
| Radishes | Sow outdoors (fall) | Jul 8 – Sep 8 |
| Kale | Sow outdoors (spring) | Apr 12 – May 2 |
| Kale | Sow outdoors (fall) | Jul 1 – Aug 8 |
| Carrots | Sow outdoors (spring) | Apr 26 – Jun 11 |
| Carrots | Sow outdoors (fall) | Jun 8 – Jul 24 |
| Garlic | Plant outdoors (fall) | Oct 8 – Nov 8 |
Where these dates come from
ZIP code 19373 is matched to the NOAA station W Chester 2 Nw, PA, 11.5 km away, at 375 ft elevation (78 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| W Chester 2 Nw, PA (used) | 375 ft | Apr 26 | Oct 18 |
| Marcus Hook, PA | 10 ft | Mar 30 | Nov 16 |
| Wilmington Porter Rsch, DE | 270 ft | Apr 7 | Nov 4 |
| Avondale 2 N, PA | 400 ft | Apr 19 | Oct 26 |
Frost dates near Thornton
- Cheyney, PA 19319 · last Apr 26, first Oct 18
- Glen Mills, PA 19342 · last Apr 26, first Oct 18
- Concordville, PA 19340 · last Apr 26, first Oct 18
- Westtown, PA 19395 · last Apr 26, first Oct 18
- Chester Heights, PA 19017 · last Apr 7, first Nov 4
- Garnet Valley, PA 19060 · last Apr 7, first Nov 4
- Chadds Ford, PA 19317 · last Apr 7, first Nov 4
- West Chester, PA 19382 · last Apr 26, first Oct 18
Frequently asked questions
- When is the last frost in Thornton, PA?
- For ZIP code 19373, the average last spring frost (32°F) is April 26, based on NOAA 1991-2020 climate normals for the W Chester 2 Nw, PA weather station. There is a 1-in-10 chance of a frost after May 11.
- When is the first frost in Thornton, PA?
- The average first fall frost (32°F) is October 18. There is a 1-in-10 chance of frost by October 4, so tender plants are at risk from that point on.
- How long is the growing season in 19373?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 174 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.