Frost dates for 18015Bethlehem, PA
The average last spring frost in Bethlehem is April 21 and the average first fall frost is October 22, giving a typical growing season of about 184 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 21
- Average first fall frost
- Oct 22
- Growing season
- 184 days
Safer after May 6 (1-in-10 risk)
Possible by Oct 7 (1-in-10 risk)
Last frost typically in 169 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 30 · Oct 10 · Oct 26 | 161 days | 100% |
| Frost / freeze (32°F) | Apr 8 · Apr 21 · May 6 | Oct 7 · Oct 22 · Nov 6 | 184 days | 100% |
| Hard freeze (28°F) | Mar 29 · Apr 8 · Apr 23 | Oct 18 · Nov 3 · Nov 17 | 208 days | 100% |
Planting calendar for Bethlehem
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 21 – May 27 |
| Tomatoes | Transplant outdoors | May 7 – Jul 2 |
| Peppers | Start seeds indoors | Mar 21 – Apr 21 |
| Peppers | Transplant outdoors | May 21 – Jun 21 |
| Eggplant | Start seeds indoors | Apr 7 – May 6 |
| Eggplant | Transplant outdoors | May 21 – Jun 21 |
| Cucumbers | Sow outdoors | May 21 – Jul 12 |
| Summer squash | Sow outdoors | May 7 – Jun 21 |
| Winter squash & pumpkins | Sow outdoors | May 21 – Jun 21 |
| Snap beans | Sow outdoors | May 7 – Aug 4 |
| Sweet corn | Sow outdoors | May 7 – Jul 2 |
| Watermelon & cantaloupe | Sow outdoors | May 21 – Jun 21 |
| Okra | Sow outdoors | May 14 – Jun 6 |
| Peas | Sow outdoors (spring) | Mar 21 – May 6 |
| Potatoes | Plant outdoors (spring) | Mar 21 – May 21 |
| Onions | Start seeds indoors (spring) | Feb 7 – Mar 6 |
| Onions | Transplant outdoors (spring) | Apr 7 – May 6 |
| Broccoli | Start seeds indoors (spring) | Mar 3 – Apr 6 |
| Broccoli | Transplant outdoors (spring) | Apr 7 – May 6 |
| Broccoli | Start seeds indoors (fall) | Jun 22 – Jul 2 |
| Broccoli | Transplant outdoors (fall) | Jul 22 – Aug 2 |
| Cabbage | Start seeds indoors (spring) | Feb 21 – Mar 21 |
| Cabbage | Transplant outdoors (spring) | Mar 21 – Apr 21 |
| Cabbage | Start seeds indoors (fall) | Jun 12 – Jul 12 |
| Cabbage | Transplant outdoors (fall) | Jul 12 – Aug 12 |
| Leaf lettuce | Sow outdoors (spring) | Mar 21 – Jun 6 |
| Leaf lettuce | Sow outdoors (fall) | Jul 12 – Aug 28 |
| Spinach | Sow outdoors (spring) | Mar 14 – Apr 27 |
| Spinach | Sow outdoors (fall) | Jul 29 – Sep 2 |
| Radishes | Sow outdoors (spring) | Mar 21 – May 11 |
| Radishes | Sow outdoors (fall) | Jul 12 – Sep 12 |
| Kale | Sow outdoors (spring) | Apr 7 – Apr 27 |
| Kale | Sow outdoors (fall) | Jul 5 – Aug 12 |
| Carrots | Sow outdoors (spring) | Apr 21 – Jun 6 |
| Carrots | Sow outdoors (fall) | Jun 12 – Jul 28 |
| Garlic | Plant outdoors (fall) | Oct 12 – Nov 12 |
Where these dates come from
ZIP code 18015 is matched to the NOAA station Springtown 1 Nne, PA, 9.2 km away, at 860 ft elevation (89 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Springtown 1 Nne, PA (used) | 860 ft | Apr 21 | Oct 22 |
| Allentown Intl Ap, PA | 390 ft | Apr 20 | Oct 24 |
| Phillipsburg-Easton Brg, NJ | 232 ft | Apr 18 | Oct 25 |
| Bucksville, PA | 387 ft | Apr 29 | Oct 16 |
Frost dates near Bethlehem
- Bethlehem, PA 18025 · last Apr 20, first Oct 24
- Hellertown, PA 18055 · last Apr 20, first Oct 24
- Allentown, PA 18109 · last Apr 20, first Oct 24
- Center Valley, PA 18034 · last Apr 20, first Oct 24
- Lehigh Valley, PA 18002 · last Apr 20, first Oct 24
- Springtown, PA 18081 · last Apr 29, first Oct 16
- Catasauqua, PA 18032 · last Apr 20, first Oct 24
- Coopersburg, PA 18036 · last Apr 29, first Oct 16
Frequently asked questions
- When is the last frost in Bethlehem, PA?
- For ZIP code 18015, the average last spring frost (32°F) is April 21, based on NOAA 1991-2020 climate normals for the Springtown 1 Nne, PA weather station. There is a 1-in-10 chance of a frost after May 6.
- When is the first frost in Bethlehem, PA?
- The average first fall frost (32°F) is October 22. There is a 1-in-10 chance of frost by October 7, so tender plants are at risk from that point on.
- How long is the growing season in 18015?
- 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.