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Frost dates and planting calendar for Allentown, Pennsylvania

Updated October 30, 2026. Based on USDA, NOAA and Colorado State University Extension data. Published by Humblebee.

USDA hardiness zone
7a[1]
Median last spring frost
Apr 20[2]
Median first fall frost
Oct 24[3]
Growing season, median
184 days[4]

Allentown, Pennsylvania is in USDA hardiness zone 7a on the 2023 map[1]. The median last spring frost at the nearby NOAA station is April 20[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Apr 6, half of years Apr 20, 1 in 10 years after May 6Last frostmedian Apr 20First fall frost: 9 in 10 years before Nov 6, half of years Oct 24, 1 in 10 years before Oct 8First frostmedian Oct 24Frost riskHardyHardy vegetables: plant Mar 23 to Apr 6Mar 23 to Apr 6Semi-hardySemi-hardy vegetables: plant Apr 6 to Apr 20Apr 6 to Apr 20TenderTender vegetables: plant around Apr 20around Apr 20Very tenderVery tender vegetables: plant from May 4from May 4
Shaded: the span between the dates frost passes in 9 of 10 years and 1 of 10 years[2][3]. Green: planting windows from the CSU rules applied to the median last frost (GardenFacts calculation)[6]. Exact dates are in the tables below.

NOAA's 1991 to 2020 records for the Allentown International Airport station give the odds[5]. In half of years the last spring frost comes after April 20, and in 1 of 10 years it comes after May 6[2]. In half of years the first fall frost comes before October 24, and in 1 of 10 years it comes before October 8[3]. These are chances from past records, not a forecast, and any year can be earlier or later[5].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after April 6 after April 20 after May 6
First fall frost (32°F)[3] before October 8 before October 24 before November 6
  • Hard freeze (28°F): median last spring date April 5, median first fall date November 4[7].
  • Frost-free growing season: at least 163 days in 9 of 10 years, 184 days in half of years and 204 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 100% of years and 28°F or colder in 100% of years[8].
  • Weather station: Allentown International Airport (USW00014737), 4.2 miles from the city center, 390 feet, 30 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension's planting guide was written for Colorado, so these dates are simple arithmetic from its rules[6]. Hardy vegetables such as broccoli, lettuce, peas and spinach can go in as early as 2 to 4 weeks before the median last frost, which is March 23 to April 6[6]. Semi-hardy vegetables such as beets, carrots and potatoes can go in as early as April 6, up to the median date itself[9]. Tender vegetables such as snap beans and sweet corn can be planted from seed around April 20[10]. Very tender vegetables such as tomatoes, peppers and eggplant typically start 2 or more weeks after the median last frost, so the earliest start is May 4[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (April 20) is March 23 to April 6[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (April 20) is April 6, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, April 20[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (April 20), is May 4[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Mar 23 May 27 (from transplants)
Cabbage (hardy)[12] Mar 23 Jun 16 (from transplants)
Kohlrabi (hardy)[12] Mar 23 May 12
Lettuce (hardy)[12] Mar 23 May 22
Onions (hardy)[12] Mar 23 Jul 11
Peas (hardy)[12] Mar 23 May 27
Radishes (hardy)[12] Mar 23 Apr 22
Spinach (hardy)[12] Mar 23 May 2
Turnips (hardy)[12] Mar 23 May 12
Beets (semi-hardy)[12] Apr 6 Jun 5
Carrots (semi-hardy)[12] Apr 6 Jun 15
Cauliflower (semi-hardy)[12] Apr 6 not listed
Parsnips (semi-hardy)[12] Apr 6 Jun 15
Potatoes (semi-hardy)[12] Apr 6 Aug 9
Swiss chard (semi-hardy)[12] Apr 6 Jun 5
Snap beans (tender)[12] Apr 20 Jun 19
Sweet corn (tender)[12] Apr 20 Jun 19
Cucumbers (tender)[12] Apr 20 Jun 14
Summer squash (tender)[12] Apr 20 Jun 9
Cantaloupe (very tender)[12] May 4 Jul 28
Eggplant (very tender)[12] May 4 Jul 3 (from transplants)
Peppers (very tender)[12] May 4 Jul 13 (from transplants)
Tomatoes (very tender)[12] May 4 Jul 8 (from transplants)
Winter squash (very tender)[12] May 4 Aug 12
Watermelon (very tender)[12] May 4 Jul 28
Spacing, depth and soil temperature (CSU Extension)
Vegetable Min. soil temp Depth Spacing Days to harvest
Broccoli[13] 40°F 1/2 in 18 in 65
Cabbage[13] 40°F 1/2 in 18 in 85
Kohlrabi[13] 40°F 1/2 in 7-9 in 50
Lettuce[13] 35°F 1/4 in 7-9 in 60
Onions[13] 35°F 1/4 in (seed), 1-2 in (sets) 4-6 in 110
Peas[13] 40°F 1 in 4-6 in 65
Radishes[13] 40°F 1/2 in 2-3 in 30
Spinach[13] 40°F 1/2 in 4-6 in 40
Turnips[13] 40°F 1/2 in 4-6 in 50
Beets[13] 40°F 3/4-1 in 4-6 in 60
Carrots[13] 40°F 1/4 in 2-3 in 70
Cauliflower[13] 40°F 1/2 in 18 in –
Parsnips[13] 35°F 1/2 in 5-6 in 70
Potatoes[13] 45°F – – 125
Swiss chard[13] 40°F 1 in 7-9 in 60
Snap beans[13] 55°F 1-1 1/2 in 6 in 60
Sweet corn[13] 50°F 1-1 1/2 in 12 x 30 in or 9 x 36 in 60-90
Cucumbers[13] 60°F 1 in 6 in trellised, 24-36 in untrellised 55
Summer squash[13] 60°F 1-1 1/2 in 36-48 in 50
Cantaloupe[13] 60°F 1-1 1/2 in 36-48 in 85
Eggplant[13] 60°F 1/4 in 18-24 in 60
Peppers[13] 60°F 1/4 in 15-18 in 70
Tomatoes[13] 50°F 1/4 in 24 in trellised 65
Winter squash[13] 60°F 1-1 1/2 in 36-48 in 100
Watermelon[13] 60°F 1-1 1/2 in 36-48 in 85

Hardiness zone

The zone comes from the USDA Plant Hardiness Zone Map, and zone 7a means an average coldest night of 0°F to 5°F over 1991 to 2020[1]. The zone is based on winter lows, not on summer heat or frost dates[14]. Allentown overlaps 5 ZIP code areas, and 98% of its land area lies in ZIP code areas rated zone 7a[15].

Zone 7a: average annual extreme minimum temperature 0°F to 5°F (1991 to 2020)[1]. Modeled value at the city center: 2.4°F[1].

Share of the city's land area by ZIP code zone: zone 7a 98%[15].

All towns in zone 7a and what zone 7a means

Zone by ZIP code
ZIP code Zone Coldest night range
18103[15] 7a 0 to 5°F
18104[15] 7a 0 to 5°F
18109[15] 7a 0 to 5°F
18102[15] 7a 0 to 5°F
18052[15] 7a 0 to 5°F

Questions people ask

What growing zone is Allentown, PA?
The center of Allentown is in USDA zone 7a on the 2023 map[1].
When is the last frost in Allentown?
The median last spring frost is April 20, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after May 6[2].
When is the first frost in Allentown?
The median first fall frost is October 24, so in half of years it comes before that date[3]. In 1 of 10 years it comes before October 8[3].
When to plant tomatoes in Allentown?
CSU Extension says very tender vegetables like tomatoes typically start 2 or more weeks after the average last frost, which works out to May 4 as the earliest start[11]. CSU's guide was written for Colorado[11].
How long is the growing season in Allentown?
The growing season is at least 184 days in half of years[4]. It is at least 163 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Allentown, Pennsylvania in zone 7a. Zone 7a means an average annual extreme minimum temperature of 0°F to 5°F over 1991 to 2020. The map's modeled value at the city center is 2.4°F. USDA zone map 2023 (PRISM, OSU)
  2. Last spring frost (32°F) at this station: in 9 of 10 years the last frost comes after April 6, in half of years after April 20, and in 1 of 10 years after May 6 (NOAA 1991 to 2020 normals). The median last frost date is April 20. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before October 8, in half of years before October 24, and in 9 of 10 years before November 6 (NOAA 1991 to 2020 normals). The median first frost date is October 24. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 163 days in 9 of 10 years, at least 184 days in half of years, and at least 204 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Allentown International Airport weather station (USW00014737), 4.2 miles from the center of Allentown at 390 feet, using 30 years of records from 1991 to 2020. NOAA Climate Normals 1991-2020
  6. Colorado State University Extension's vegetable planting guide (written for Colorado) groups broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips as hardy vegetables, with this rule: as early as 2-4 weeks before the average last... CSU Extension GardenNotes #720
  7. Hard freeze (28°F) at this station: the median last spring date is April 5 and the median first fall date is November 4. NOAA Climate Normals 1991-2020
  8. At this station the low reached 32°F or colder in 100% of years from 1991 to 2020, and 28°F or colder in 100% of years. NOAA Climate Normals 1991-2020
  9. Colorado State University Extension's vegetable planting guide (written for Colorado) groups beets, carrots, cauliflower, parsnips, potatoes, Swiss chard as semi-hardy vegetables, with this rule: as early as 0-2 weeks before the average last spring frost.... CSU Extension GardenNotes #720
  10. Colorado State University Extension's vegetable planting guide (written for Colorado) groups snap beans, sweet corn, cucumbers, summer squash as tender vegetables, with this rule: from seed around the average last spring frost; cucumber and summer squash... CSU Extension GardenNotes #720
  11. Colorado State University Extension's vegetable planting guide (written for Colorado) groups cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon as very tender vegetables, with this rule: typically 2 or more weeks after the average last... CSU Extension GardenNotes #720
  12. GardenFacts calculation: earliest planting date plus CSU days to harvest (table on this page), from the station's median last frost. NOAA Climate Normals 1991-2020
  13. CSU Extension vegetable table: soil temperature, depth, spacing, days to harvest (table on this page). CSU Extension GardenNotes #720
  14. USDA hardiness zones are based on the average annual extreme minimum winter temperature (the coldest night of each winter, averaged over 1991 to 2020 for the 2023 map), not on summer heat or frost dates. Each zone spans 10°F and each half zone (a or b)... USDA Plant Hardiness Zone Map
  15. Allentown, Pennsylvania overlaps 5 ZIP code areas. By land area, 98% lies in ZIP code areas rated zone 7a. USDA zone map 2023 (PRISM, OSU)

Frost dates are probabilities from 1991 to 2020 weather records at one NOAA station, not a forecast. Any year can be earlier or later. The hardiness zone describes the average coldest winter night, not frost dates or summer heat. Spots inside the city can differ (ZIP table). Planting rules come from Colorado State University Extension's guide, written for Colorado. A local extension office may give dates tuned to the area. Planting and harvest dates marked GardenFacts calculation are simple arithmetic from the facts above, not advice from the source.

Hardiness zone data: USDA Plant Hardiness Zone Map (2023), USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu, accessed October 30, 2026. This is not the official USDA map. Frost data: NOAA NCEI U.S. Climate Normals 1991-2020. Planting rules: Colorado State University Extension.