Bethlehem, Pennsylvania: planting zone & frost dates
Bethlehem is in USDA plant hardiness zone 7a, where the average coldest winter night reaches 0 to 5°F (-17.8 to -15.0°C). The typical last spring frost is around Apr 26 and the first fall frost around Oct 17.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 6 | Oct 8 |
| Typical planning date (30% risk) | Apr 26 | Oct 17 |
| Median (50%) | Apr 20 | Oct 24 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station ALLENTOWN INTL AP, PA (USW00014737), 4.6 mi (7.4 km) from the city center and 43 ft higher than the city center (+13 m). Record used for the 1991–2020 normals: 30 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Bethlehem
All 3 ZIP codes covering Bethlehem are in zone 7a.
Vegetable planting calendar for Bethlehem
Dates are counted from the 30%-risk frost dates above (last frost Apr 26, first frost Oct 17). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 1 – Mar 15 | May 3 – May 17 | — | — |
| Pepper | Feb 15 – Mar 1 | May 10 – May 24 | — | — |
| Lettuce | Mar 15 – Mar 29 | Apr 12 – May 3 | Mar 29 – May 10 | Aug 8 – Sep 5 |
| Green Beans | — | — | May 3 – Jun 7 | Jul 25 – Aug 8 |
| Sweet Corn | — | — | May 3 – May 31 | — |
| Zucchini & Summer Squash | Mar 29 – Apr 5 | May 3 – May 17 | May 3 – May 24 | Jul 25 – Aug 8 |
| Cucumber | Mar 29 – Apr 5 | May 10 – May 17 | May 3 – May 24 | Jul 25 – Aug 8 |
| Carrot | — | — | Apr 5 – May 10 | Jul 25 – Aug 8 |
| Onion | Feb 1 – Feb 15 | Mar 29 – Apr 12 | — | — |
| Potato | — | Mar 29 – Apr 19 | — | — |
| Basil | Mar 15 – Mar 29 | May 10 – May 24 | May 10 – May 31 | — |
| Spinach | — | — | Mar 15 – Apr 12 | Aug 22 – Sep 19 |
| Kale | Mar 1 – Mar 15 | Mar 29 – Apr 19 | Mar 29 – Apr 19 | Aug 8 – Sep 5 |
| Broccoli | Mar 1 – Mar 15 | Apr 12 – May 3 | — | Jul 25 – Aug 8 |
| Peas | — | — | Mar 15 – Apr 5 | Aug 8 – Aug 22 |
| Eggplant | Feb 15 – Mar 1 | May 10 – May 24 | — | — |
| Cabbage | Mar 1 – Mar 15 | Mar 29 – Apr 12 | — | Jul 25 – Aug 8 |
| Radish | — | — | Mar 22 – May 10 | Sep 5 – Oct 3 |
| Strawberry | — | Mar 29 – Apr 19 | — | — |
| Beets | — | — | Apr 5 – May 17 | Aug 8 – Aug 22 |
Nearby cities in Pennsylvania
- Allentown — zone 7a, last frost Apr 26, first frost Oct 17
- Reading — zone 7a, last frost Apr 21, first frost Oct 22
- Philadelphia — zone 7b, last frost Apr 4, first frost Nov 11
- Pittsburgh — zone 6b, last frost Apr 24, first frost Oct 22
- Erie — zone 6b, last frost May 2, first frost Oct 30
More: all Pennsylvania cities · other zone 7a cities: Louisville, KY, Wichita, KS, Cleveland, OH, Lexington, KY, St. Louis, MO, Boise, ID, Amarillo, TX, Providence, RI
Bethlehem gardening questions
When is the last frost in Bethlehem, PA?
Plan around Apr 26. At NOAA's Allentown Int'l Airport, PA station, 4.6 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Apr 20, and after May 6 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 5. The 90% and 10% dates are 30 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Bethlehem, PA?
Start seeds indoors Mar 1 – Mar 15 and set transplants outside May 3 – May 17, once nights stay above 50°F and the soil is near 60°F. That leaves 174 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Bethlehem?
About 184 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 163 days, and in 1 year in 10 it runs 204 days or more. In fall there is a 10% chance of frost by Oct 8 and a 30% chance by Oct 17. That is the shortest of the 6 Pennsylvania cities on this site.
When should I plant a fall garden in Bethlehem?
Count back from the first fall frost (Oct 17): transplant broccoli Jul 25 – Aug 8; sow kale Aug 8 – Sep 5; sow lettuce Aug 8 – Sep 5; sow radishes Sep 5 – Oct 3. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Nov 4. How the math works: succession and fall planting.
Did Bethlehem's hardiness zone change on the 2023 map?
Yes. Most of Bethlehem was zone 6b on the 2012 map and is zone 7a on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.
How does Bethlehem compare with Reading, PA?
Both are in zone 7a. The typical last spring frost in Bethlehem (Apr 26) comes about 5 days later than in Reading, PA (Apr 21), 35 miles away, and the first fall frost is Oct 17 versus Oct 22. The two cities use different NOAA stations.