Frost dates for 18103Allentown, PA
The average last spring frost in Allentown is April 20 and the average first fall frost is October 24, giving a typical growing season of about 184 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 20
- Average first fall frost
- Oct 24
- Growing season
- 184 days
Safer after May 6 (1-in-10 risk)
Possible by Oct 8 (1-in-10 risk)
Last frost typically in 168 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 19 · May 2 · May 18 | Sep 29 · Oct 12 · Oct 28 | 161 days | 100% |
| Frost / freeze (32°F) | Apr 6 · Apr 20 · May 6 | Oct 8 · Oct 24 · Nov 6 | 184 days | 100% |
| Hard freeze (28°F) | Mar 23 · Apr 5 · Apr 18 | Oct 19 · Nov 4 · Nov 18 | 211 days | 100% |
Planting calendar for Allentown
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 20 – May 26 |
| Tomatoes | Transplant outdoors | May 6 – Jul 4 |
| Peppers | Start seeds indoors | Mar 20 – Apr 20 |
| Peppers | Transplant outdoors | May 20 – Jun 20 |
| Eggplant | Start seeds indoors | Apr 6 – May 5 |
| Eggplant | Transplant outdoors | May 20 – Jun 20 |
| Cucumbers | Sow outdoors | May 20 – Jul 14 |
| Summer squash | Sow outdoors | May 6 – Jun 20 |
| Winter squash & pumpkins | Sow outdoors | May 20 – Jun 20 |
| Snap beans | Sow outdoors | May 6 – Aug 6 |
| Sweet corn | Sow outdoors | May 6 – Jul 4 |
| Watermelon & cantaloupe | Sow outdoors | May 20 – Jun 20 |
| Okra | Sow outdoors | May 13 – Jun 5 |
| Peas | Sow outdoors (spring) | Mar 20 – May 5 |
| Potatoes | Plant outdoors (spring) | Mar 20 – May 20 |
| Onions | Start seeds indoors (spring) | Feb 6 – Mar 5 |
| Onions | Transplant outdoors (spring) | Apr 6 – May 5 |
| Broccoli | Start seeds indoors (spring) | Mar 2 – Apr 5 |
| Broccoli | Transplant outdoors (spring) | Apr 6 – May 5 |
| Broccoli | Start seeds indoors (fall) | Jun 24 – Jul 4 |
| Broccoli | Transplant outdoors (fall) | Jul 24 – Aug 4 |
| Cabbage | Start seeds indoors (spring) | Feb 20 – Mar 20 |
| Cabbage | Transplant outdoors (spring) | Mar 20 – Apr 20 |
| Cabbage | Start seeds indoors (fall) | Jun 14 – Jul 14 |
| Cabbage | Transplant outdoors (fall) | Jul 14 – Aug 14 |
| Leaf lettuce | Sow outdoors (spring) | Mar 20 – Jun 5 |
| Leaf lettuce | Sow outdoors (fall) | Jul 14 – Aug 30 |
| Spinach | Sow outdoors (spring) | Mar 13 – Apr 26 |
| Spinach | Sow outdoors (fall) | Jul 31 – Sep 4 |
| Radishes | Sow outdoors (spring) | Mar 20 – May 10 |
| Radishes | Sow outdoors (fall) | Jul 14 – Sep 14 |
| Kale | Sow outdoors (spring) | Apr 6 – Apr 26 |
| Kale | Sow outdoors (fall) | Jul 7 – Aug 14 |
| Carrots | Sow outdoors (spring) | Apr 20 – Jun 5 |
| Carrots | Sow outdoors (fall) | Jun 14 – Jul 30 |
| Garlic | Plant outdoors (fall) | Oct 14 – Nov 14 |
Where these dates come from
ZIP code 18103 is matched to the NOAA station Allentown Intl Ap, PA, 7 km away, at 390 ft elevation (98 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Allentown Intl Ap, PA (used) | 390 ft | Apr 20 | Oct 24 |
| Springtown 1 Nne, PA | 860 ft | Apr 21 | Oct 22 |
| Rodale Rsch Ctr, PA | 550 ft | Apr 26 | Oct 14 |
| Bucksville, PA | 387 ft | Apr 29 | Oct 16 |
Frost dates near Allentown
- Allentown, PA 18101 · last Apr 20, first Oct 24
- Emmaus, PA 18098 · last Apr 20, first Oct 24
- Center Valley, PA 18034 · last Apr 20, first Oct 24
- Bethlehem, PA 18015 · last Apr 21, first Oct 22
- Catasauqua, PA 18032 · last Apr 20, first Oct 24
- Whitehall, PA 18052 · last Apr 20, first Oct 24
- Limeport, PA 18060 · last Apr 20, first Oct 24
- Lehigh Valley, PA 18002 · last Apr 20, first Oct 24
Frequently asked questions
- When is the last frost in Allentown, PA?
- For ZIP code 18103, the average last spring frost (32°F) is April 20, based on NOAA 1991-2020 climate normals for the Allentown Intl Ap, PA weather station. There is a 1-in-10 chance of a frost after May 6.
- When is the first frost in Allentown, PA?
- The average first fall frost (32°F) is October 24. There is a 1-in-10 chance of frost by October 8, so tender plants are at risk from that point on.
- How long is the growing season in 18103?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 184 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.