Frost dates for Allentown, Pennsylvania
In Allentown, half of springs have had their last frost by April 20 (and 1 spring in 10 still has one after May 6), and half of falls have had their first frost by October 24, leaving about 184 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Allentown, Pennsylvania
Last spring frost
April 20
Half of springs have their last frost by this date. For a safer bet, wait until May 6: only 1 spring in 10 has a frost after that.
First fall frost
October 24
Half of falls have their first frost by this date. In 1 fall in 10 it comes by October 8.
Growing season
184 days
Frost-free days in a typical year. 9 years in 10 get at least 163.
Hardiness zone
Not listed
This ZIP code isn't in the USDA's ZIP code list for the 2023 map.
Print a year planner for Allentown
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | April 6 | April 20 | May 6 |
| First frost in fall | October 8 | October 24 | November 6 |
The frost-free season between them runs 184 days in a typical year. In 1 year in 10 it is 204 days or longer, and in 1 year in 10 it is 163 days or shorter.
- Hard freeze (28°F): typically last on April 5 and first on November 4. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on May 2 and first on October 12. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Allentown comes between April 6 and May 6, a window of 30 days. That is about average for NOAA's stations (the typical window is 31 days).
Among Pennsylvania's 160 NOAA stations with a frost every year, 76 percent have their typical last frost later than Allentown does.
Planting calendar for Allentown
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
| When | What to do | Why then |
|---|---|---|
| February | ||
| February 2 to March 2 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February 16 to March 16 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March | ||
| March 2 to 23 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 9 to 23 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 16 to 30 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| March 23 to April 6 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| March 23 to April 6 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April | ||
| April 6 to 20 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 6 to 20 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| April 20 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May | ||
| May 4 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 4 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| May 29 to June 12 | Cabbage for fall Start seeds | set the plants out by July 17 |
| June | ||
| June 18 to July 2 | Broccoli for fall Start seeds | set the plants out by August 6 |
| July | ||
| July 28 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August | ||
| August 1 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| August 2 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August 6 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| August 7 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August 11 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August 21 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August 31 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 10 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| October | ||
| October 8 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| November | ||
| November 11 to 18 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 16 days later. That plans around May 6, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Allentown International Airport (station USW00014737), 4 miles from the center of Allentown. It sits at about the same elevation, 390 feet above sea level. NOAA rates this station's record as standard: at least 24 of the 30 years, with gaps filled from nearby stations.
The same station also gives the frost dates for Bethlehem, Emmaus and Northampton.
Our ZIP code lookup matches these 22 ZIP codes to the same station, so they get the same dates: 18012, 18015, 18017, 18018, 18020, 18032, 18034, 18035, 18037, 18046, 18052, 18059, 18064, 18067, 18086, 18088, 18101, 18102, 18103, 18104, 18106, 18109. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Philadelphia, Pennsylvania: last frost around April 4, first frost around November 7 (45 miles away)
- Trenton, New Jersey: last frost around April 10, first frost around November 1 (45 miles away)
- Wilmington, Delaware: last frost around April 7, first frost around November 1 (60 miles away)
See frost dates across Pennsylvania, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.