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Frost dates and planting calendar for Green Bay, Wisconsin

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

USDA hardiness zone
5b[1]
Median last spring frost
Apr 30[2]
Median first fall frost
Oct 9[3]
Growing season, median
161 days[4]

Green Bay, Wisconsin is in USDA hardiness zone 5b[1]. The median last spring frost is April 30, so in half of years the last frost comes after that date[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Apr 16, half of years Apr 30, 1 in 10 years after May 16Last frostmedian Apr 30First fall frost: 9 in 10 years before Oct 26, half of years Oct 9, 1 in 10 years before Sep 24First frostmedian Oct 9Frost riskHardyHardy vegetables: plant Apr 2 to Apr 16Apr 2 to Apr 16Semi-hardySemi-hardy vegetables: plant Apr 16 to Apr 30Apr 16 to Apr 30TenderTender vegetables: plant around Apr 30around Apr 30Very tenderVery tender vegetables: plant from May 14from May 14
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.

These frost dates come from NOAA climate normals for the Green Bay weather station, using records from 1991 to 2020[5]. For the last spring frost, 9 of 10 years see a frost after April 16, half of years see one after April 30, and 1 of 10 years sees one after May 16[2]. For the first fall frost, 1 of 10 years sees one before September 24, half of years before October 9, and 9 of 10 years before October 26[3]. These are chances from past records and not a forecast, so any year can come earlier or later[2][3]. The growing season is at least 161 days in half of years[4].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after April 16 after April 30 after May 16
First fall frost (32°F)[3] before September 24 before October 9 before October 26
  • Hard freeze (28°F): median last spring date April 17, median first fall date October 24[7].
  • Frost-free growing season: at least 141 days in 9 of 10 years, 161 days in half of years and 181 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: Green Bay (USW00014898), 6.3 miles from the city center, 682 feet, 30 years of 1991 to 2020 records[5].

When to plant vegetables

The planting groups come from Colorado State University Extension's vegetable guide, which was written for Colorado[6]. GardenFacts used the NOAA median last frost of April 30 as the average last frost[6]. Hardy vegetables such as peas, spinach and lettuce can go in as early as 2 to 4 weeks before that date, which is April 2 to April 16[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as April 16, up to the median date itself[9]. Tender vegetables such as snap beans and sweet corn can be planted from seed around April 30[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after the last frost, and the earliest start is May 14[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (April 30) is April 2 to April 16[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (April 30) is April 16, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, April 30[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (April 30), is May 14[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Apr 2 Jun 6 (from transplants)
Cabbage (hardy)[12] Apr 2 Jun 26 (from transplants)
Kohlrabi (hardy)[12] Apr 2 May 22
Lettuce (hardy)[12] Apr 2 Jun 1
Onions (hardy)[12] Apr 2 Jul 21
Peas (hardy)[12] Apr 2 Jun 6
Radishes (hardy)[12] Apr 2 May 2
Spinach (hardy)[12] Apr 2 May 12
Turnips (hardy)[12] Apr 2 May 22
Beets (semi-hardy)[12] Apr 16 Jun 15
Carrots (semi-hardy)[12] Apr 16 Jun 25
Cauliflower (semi-hardy)[12] Apr 16 not listed
Parsnips (semi-hardy)[12] Apr 16 Jun 25
Potatoes (semi-hardy)[12] Apr 16 Aug 19
Swiss chard (semi-hardy)[12] Apr 16 Jun 15
Snap beans (tender)[12] Apr 30 Jun 29
Sweet corn (tender)[12] Apr 30 Jun 29
Cucumbers (tender)[12] Apr 30 Jun 24
Summer squash (tender)[12] Apr 30 Jun 19
Cantaloupe (very tender)[12] May 14 Aug 7
Eggplant (very tender)[12] May 14 Jul 13 (from transplants)
Peppers (very tender)[12] May 14 Jul 23 (from transplants)
Tomatoes (very tender)[12] May 14 Jul 18 (from transplants)
Winter squash (very tender)[12] May 14 Aug 22
Watermelon (very tender)[12] May 14 Aug 7
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

Zone 5b means the coldest night of the winter averages -15°F to -10°F over 1991 to 2020[1]. The zone is based on that winter low and not on summer heat or frost dates[14]. USDA describes the map as the standard gardeners use to judge which perennial plants are most likely to thrive[14]. All of Green Bay by land area sits in ZIP code areas rated zone 5b[15].

Zone 5b: average annual extreme minimum temperature -15°F to -10°F (1991 to 2020)[1]. Modeled value at the city center: -14.4°F[1].

Share of the city's land area by ZIP code zone: zone 5b 100%[15].

All towns in zone 5b and what zone 5b means

Zone by ZIP code
ZIP code Zone Coldest night range
54311[15] 5b -15 to -10°F
54302[15] 5b -15 to -10°F
54303[15] 5b -15 to -10°F
54304[15] 5b -15 to -10°F
54313[15] 5b -15 to -10°F
54229[15] 5b -15 to -10°F
54301[15] 5b -15 to -10°F
54155[15] 5b -15 to -10°F

Questions people ask

What growing zone is Green Bay, Wisconsin?
The 2023 USDA map puts the center of Green Bay in zone 5b[1]. By land area, 100% of the city lies in ZIP code areas rated 5b[15].
When is the last frost in Green Bay?
The median last spring frost is April 30, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after May 16[2].
When is the first frost in Green Bay?
The median first fall frost is October 9, so in half of years the first frost comes before that date[3]. In 1 of 10 years it comes before September 24[3].
When to plant tomatoes in Green Bay?
CSU Extension typically says very tender vegetables like tomatoes wait 2 or more weeks after the average last frost[11]. Using the April 30 median, the earliest start is May 14[11].
How long is the growing season in Green Bay?
The growing season is at least 161 days in half of years[4]. It is at least 141 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Green Bay, Wisconsin in zone 5b. Zone 5b means an average annual extreme minimum temperature of -15°F to -10°F over 1991 to 2020. The map's modeled value at the city center is minus 14.4°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 16, in half of years after April 30, and in 1 of 10 years after May 16 (NOAA 1991 to 2020 normals). The median last frost date is April 30. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before September 24, in half of years before October 9, and in 9 of 10 years before October 26 (NOAA 1991 to 2020 normals). The median first frost date is October 9. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 141 days in 9 of 10 years, at least 161 days in half of years, and at least 181 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Green Bay weather station (USW00014898), 6.3 miles from the center of Green Bay at 682 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 17 and the median first fall date is October 24. 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. Green Bay, Wisconsin overlaps 8 ZIP code areas. By land area, 100% lies in ZIP code areas rated zone 5b. 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.