Frost dates for 19403Norristown, PA
The average last spring frost in Norristown is April 24 and the average first fall frost is October 15, giving a typical growing season of about 173 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 24
- Average first fall frost
- Oct 15
- Growing season
- 173 days
Safer after May 9 (1-in-10 risk)
Possible by Oct 1 (1-in-10 risk)
Last frost typically in 172 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 21 · May 4 · May 21 | Sep 21 · Oct 4 · Oct 18 | 151 days | 100% |
| Frost / freeze (32°F) | Apr 10 · Apr 24 · May 9 | Oct 1 · Oct 15 · Nov 1 | 173 days | 100% |
| Hard freeze (28°F) | Mar 28 · Apr 10 · Apr 27 | Oct 10 · Oct 27 · Nov 12 | 198 days | 100% |
Planting calendar for Norristown
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 24 – May 30 |
| Tomatoes | Transplant outdoors | May 10 – Jun 25 |
| Peppers | Start seeds indoors | Mar 24 – Apr 24 |
| Peppers | Transplant outdoors | May 24 – Jun 24 |
| Eggplant | Start seeds indoors | Apr 10 – May 9 |
| Eggplant | Transplant outdoors | May 24 – Jun 24 |
| Cucumbers | Sow outdoors | May 24 – Jul 5 |
| Summer squash | Sow outdoors | May 10 – Jun 24 |
| Winter squash & pumpkins | Sow outdoors | May 24 – Jun 24 |
| Snap beans | Sow outdoors | May 10 – Jul 28 |
| Sweet corn | Sow outdoors | May 10 – Jun 25 |
| Watermelon & cantaloupe | Sow outdoors | May 24 – Jun 24 |
| Okra | Sow outdoors | May 17 – Jun 9 |
| Peas | Sow outdoors (spring) | Mar 24 – May 9 |
| Potatoes | Plant outdoors (spring) | Mar 24 – May 24 |
| Onions | Start seeds indoors (spring) | Feb 10 – Mar 9 |
| Onions | Transplant outdoors (spring) | Apr 10 – May 9 |
| Broccoli | Start seeds indoors (spring) | Mar 6 – Apr 9 |
| Broccoli | Transplant outdoors (spring) | Apr 10 – May 9 |
| Broccoli | Start seeds indoors (fall) | Jun 15 – Jun 25 |
| Broccoli | Transplant outdoors (fall) | Jul 15 – Jul 26 |
| Cabbage | Start seeds indoors (spring) | Feb 24 – Mar 24 |
| Cabbage | Transplant outdoors (spring) | Mar 24 – Apr 24 |
| Cabbage | Start seeds indoors (fall) | Jun 5 – Jul 5 |
| Cabbage | Transplant outdoors (fall) | Jul 5 – Aug 5 |
| Leaf lettuce | Sow outdoors (spring) | Mar 24 – Jun 9 |
| Leaf lettuce | Sow outdoors (fall) | Jul 5 – Aug 21 |
| Spinach | Sow outdoors (spring) | Mar 17 – Apr 30 |
| Spinach | Sow outdoors (fall) | Jul 22 – Aug 26 |
| Radishes | Sow outdoors (spring) | Mar 24 – May 14 |
| Radishes | Sow outdoors (fall) | Jul 5 – Sep 5 |
| Kale | Sow outdoors (spring) | Apr 10 – Apr 30 |
| Kale | Sow outdoors (fall) | Jun 28 – Aug 5 |
| Carrots | Sow outdoors (spring) | Apr 24 – Jun 9 |
| Carrots | Sow outdoors (fall) | Jun 5 – Jul 21 |
| Garlic | Plant outdoors (fall) | Oct 5 – Nov 5 |
Where these dates come from
ZIP code 19403 is matched to the NOAA station Graterford 1 E, PA, 9.6 km away, at 279 ft elevation (10 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Graterford 1 E, PA (used) | 279 ft | Apr 24 | Oct 15 |
| Norristown, PA | 62 ft | Apr 8 | Oct 31 |
| Phoenixville 1 E, PA | 85 ft | Apr 18 | Oct 27 |
| Pottstown Limerick Ap, PA | 291 ft | Apr 20 | Oct 23 |
Frost dates near Norristown
- Fairview Village, PA 19409 · last Apr 24, first Oct 15
- Eagleville, PA 19415 · last Apr 24, first Oct 15
- Norristown, PA 19401 · last Apr 8, first Oct 31
- Worcester, PA 19490 · last Apr 24, first Oct 15
- Creamery, PA 19430 · last Apr 24, first Oct 15
- King Of Prussia, PA 19406 · last Apr 8, first Oct 31
- Bridgeport, PA 19405 · last Apr 8, first Oct 31
- Collegeville, PA 19426 · last Apr 24, first Oct 15
Frequently asked questions
- When is the last frost in Norristown, PA?
- For ZIP code 19403, the average last spring frost (32°F) is April 24, based on NOAA 1991-2020 climate normals for the Graterford 1 E, PA weather station. There is a 1-in-10 chance of a frost after May 9.
- When is the first frost in Norristown, PA?
- The average first fall frost (32°F) is October 15. There is a 1-in-10 chance of frost by October 1, so tender plants are at risk from that point on.
- How long is the growing season in 19403?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 173 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.