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Frost dates and planting calendar for Chicago, Illinois

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

USDA hardiness zone
6a[1]
Median last spring frost
Apr 10[2]
Median first fall frost
Nov 1[3]
Growing season, median
203 days[4]

Chicago sits in USDA hardiness zone 6a at the city center[1]. At the nearby NOAA station, the median last spring frost is April 10[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Mar 30, half of years Apr 10, 1 in 10 years after Apr 26Last frostmedian Apr 10First fall frost: 9 in 10 years before Nov 16, half of years Nov 1, 1 in 10 years before Oct 21First frostmedian Nov 1Frost riskHardyHardy vegetables: plant Mar 13 to Mar 27Mar 13 to Mar 27Semi-hardySemi-hardy vegetables: plant Mar 27 to Apr 10Mar 27 to Apr 10TenderTender vegetables: plant around Apr 10around Apr 10Very tenderVery tender vegetables: plant from Apr 24from Apr 24
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 Chicago Midway Airport 3SW station, based on records from 1991 to 2020[5]. In half of years, the last spring frost falls after April 10, and in 1 of 10 years it comes after April 26[2]. In the fall, half of years see a first frost before November 1, and 1 of 10 years see one before October 21[3]. Treat these as odds, not a forecast. Any year can run earlier or later.

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after March 30 after April 10 after April 26
First fall frost (32°F)[3] before October 21 before November 1 before November 16
  • Hard freeze (28°F): median last spring date April 1, median first fall date November 11[7].
  • Frost-free growing season: at least 183 days in 9 of 10 years, 203 days in half of years and 224 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: Chicago Midway Airport 3SW (USC00111577), 8.4 miles from the city center, 620 feet, 30 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension sorts vegetables into groups by how much cold they can take, and its guide was written for Colorado. We use the NOAA median last frost of April 10 as the average date for Chicago[6]. That puts the earliest window for hardy crops like peas, lettuce and spinach[9] at March 13 to March 27[6]. Semi-hardy crops like beets and carrots[10] fit from March 27 up to April 10[11], and tender crops like snap beans and sweet corn[12] go in around April 10[13]. Very tender crops like tomatoes and peppers[14] wait until about April 24[15].

  • Hardy: 2 to 4 weeks before the median last frost (April 10) is March 13 to March 27[6][9]
  • Semi-hardy: 2 weeks before the median last frost (April 10) is March 27, up to the median date itself[11][10]
  • Tender: around the median last frost date, April 10[13][12]
  • Very tender: two weeks after the median last frost (April 10) is April 24[15][14]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[16] Mar 13 May 17 (from transplants)
Cabbage (hardy)[16] Mar 13 Jun 6 (from transplants)
Kohlrabi (hardy)[16] Mar 13 May 2
Lettuce (hardy)[16] Mar 13 May 12
Onions (hardy)[16] Mar 13 Jul 1
Peas (hardy)[16] Mar 13 May 17
Radishes (hardy)[16] Mar 13 Apr 12
Spinach (hardy)[16] Mar 13 Apr 22
Turnips (hardy)[16] Mar 13 May 2
Beets (semi-hardy)[16] Mar 27 May 26
Carrots (semi-hardy)[16] Mar 27 Jun 5
Cauliflower (semi-hardy)[16] Mar 27 not listed
Parsnips (semi-hardy)[16] Mar 27 Jun 5
Potatoes (semi-hardy)[16] Mar 27 Jul 30
Swiss chard (semi-hardy)[16] Mar 27 May 26
Snap beans (tender)[16] Apr 10 Jun 9
Sweet corn (tender)[16] Apr 10 Jun 9
Cucumbers (tender)[16] Apr 10 Jun 4
Summer squash (tender)[16] Apr 10 May 30
Cantaloupe (very tender)[16] Apr 24 Jul 18
Eggplant (very tender)[16] Apr 24 Jun 23 (from transplants)
Peppers (very tender)[16] Apr 24 Jul 3 (from transplants)
Tomatoes (very tender)[16] Apr 24 Jun 28 (from transplants)
Winter squash (very tender)[16] Apr 24 Aug 2
Watermelon (very tender)[16] Apr 24 Jul 18
Spacing, depth and soil temperature (CSU Extension)
Vegetable Min. soil temp Depth Spacing Days to harvest
Broccoli[17] 40°F 1/2 in 18 in 65
Cabbage[17] 40°F 1/2 in 18 in 85
Kohlrabi[17] 40°F 1/2 in 7-9 in 50
Lettuce[17] 35°F 1/4 in 7-9 in 60
Onions[17] 35°F 1/4 in (seed), 1-2 in (sets) 4-6 in 110
Peas[17] 40°F 1 in 4-6 in 65
Radishes[17] 40°F 1/2 in 2-3 in 30
Spinach[17] 40°F 1/2 in 4-6 in 40
Turnips[17] 40°F 1/2 in 4-6 in 50
Beets[17] 40°F 3/4-1 in 4-6 in 60
Carrots[17] 40°F 1/4 in 2-3 in 70
Cauliflower[17] 40°F 1/2 in 18 in –
Parsnips[17] 35°F 1/2 in 5-6 in 70
Potatoes[17] 45°F – – 125
Swiss chard[17] 40°F 1 in 7-9 in 60
Snap beans[17] 55°F 1-1 1/2 in 6 in 60
Sweet corn[17] 50°F 1-1 1/2 in 12 x 30 in or 9 x 36 in 60-90
Cucumbers[17] 60°F 1 in 6 in trellised, 24-36 in untrellised 55
Summer squash[17] 60°F 1-1 1/2 in 36-48 in 50
Cantaloupe[17] 60°F 1-1 1/2 in 36-48 in 85
Eggplant[17] 60°F 1/4 in 18-24 in 60
Peppers[17] 60°F 1/4 in 15-18 in 70
Tomatoes[17] 50°F 1/4 in 24 in trellised 65
Winter squash[17] 60°F 1-1 1/2 in 36-48 in 100
Watermelon[17] 60°F 1-1 1/2 in 36-48 in 85

Hardiness zone

The zone number reflects the average coldest winter night, not summer heat or frost dates[18]. Zone 6a covers an average yearly low of -10°F to -5°F[1]. Chicago spans two zones: by land area of its ZIP code areas, 89% is in zone 6a and 11% is in zone 6b[19].

Zone 6a: average annual extreme minimum temperature -10°F to -5°F (1991 to 2020)[1]. Modeled value at the city center: -5.1°F[1].

Share of the city's land area by ZIP code zone: zone 6a 89%, zone 6b 11%[19].

All towns in zone 6a and what zone 6a means

Zone by ZIP code
ZIP code Zone Coldest night range
60617[19] 6a -10 to -5°F
60628[19] 6a -10 to -5°F
60633[19] 6a -10 to -5°F
60018[19] 6a -10 to -5°F
60609[19] 6a -10 to -5°F
60632[19] 6a -10 to -5°F
60643[19] 6a -10 to -5°F
60634[19] 6a -10 to -5°F
60629[19] 6a -10 to -5°F
60620[19] 6a -10 to -5°F
60608[19] 6a -10 to -5°F
60619[19] 6a -10 to -5°F
60638[19] 6a -10 to -5°F
60623[19] 6a -10 to -5°F
60618[19] 6a -10 to -5°F
60639[19] 6a -10 to -5°F
60652[19] 6a -10 to -5°F
60630[19] 6a -10 to -5°F
60637[19] 6a -10 to -5°F
60646[19] 6a -10 to -5°F
60655[19] 6a -10 to -5°F
60641[19] 6a -10 to -5°F
60647[19] 6a -10 to -5°F
60636[19] 6a -10 to -5°F
60616[19] 6b -5 to 0°F
60625[19] 6a -10 to -5°F
60621[19] 6a -10 to -5°F
60612[19] 6a -10 to -5°F
60631[19] 6a -10 to -5°F
60649[19] 6b -5 to 0°F

Questions people ask

What growing zone is Chicago?
The 2023 USDA map places the center of Chicago in zone 6a[1]. Some parts of the city fall in zone 6b[19].
When is the last frost in Chicago?
At the NOAA station near Midway Airport[5], the median last spring frost is April 10[2]. In 1 of 10 years it comes after April 26[2].
When to plant tomatoes in Chicago?
CSU Extension puts tomatoes in its very tender group, planted 2 or more weeks after the average last frost[14]. For Chicago that works out to about April 24[15].
When is the first frost in Chicago?
The median first fall frost is November 1[3]. In 1 of 10 years it arrives before October 21[3].
How long is the growing season in Chicago?
In half of years, the stretch between the last spring frost and first fall frost is at least 203 days[4]. In 9 of 10 years it is at least 183 days[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Chicago, Illinois in zone 6a. Zone 6a means an average annual extreme minimum temperature of -10°F to -5°F over 1991 to 2020. The map's modeled value at the city center is minus 5.1°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 March 30, in half of years after April 10, and in 1 of 10 years after April 26 (NOAA 1991 to 2020 normals). The median last frost date is April 10. 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 21, in half of years before November 1, and in 9 of 10 years before November 16 (NOAA 1991 to 2020 normals). The median first frost date is November 1. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 183 days in 9 of 10 years, at least 203 days in half of years, and at least 224 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Chicago Midway Airport 3SW weather station (USC00111577), 8.4 miles from the center of Chicago at 620 feet, using 30 years of records from 1991 to 2020. NOAA Climate Normals 1991-2020
  6. GardenFacts calculation for Chicago: taking the NOAA median (50%) last frost date as the average last frost and applying the CSU rule for hardy vegetables, 2 to 4 weeks before the median last frost (April 10) is March 13 to March 27. NOAA Climate Normals 1991-2020
  7. Hard freeze (28°F) at this station: the median last spring date is April 1 and the median first fall date is November 11. 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 groups broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips as hardy vegetables. Its rule for planting them: as early as 2-4 weeks before the average last spring frost. CSU Extension GardenNotes #720
  10. Colorado State University Extension's vegetable planting guide groups beets, carrots, cauliflower, parsnips, potatoes, Swiss chard as semi-hardy vegetables. Its rule for planting them: as early as 0-2 weeks before the average last spring frost. CSU Extension GardenNotes #720
  11. GardenFacts calculation for Chicago: taking the NOAA median (50%) last frost date as the average last frost and applying the CSU rule for semi-hardy vegetables, 2 weeks before the median last frost (April 10) is March 27, up to the median date itself. NOAA Climate Normals 1991-2020
  12. Colorado State University Extension's vegetable planting guide groups snap beans, sweet corn, cucumbers, summer squash as tender vegetables. Its rule for planting them: from seed around the average last spring frost; cucumber and summer squash transplants... CSU Extension GardenNotes #720
  13. GardenFacts calculation for Chicago: taking the NOAA median (50%) last frost date as the average last frost and applying the CSU rule for tender vegetables, around the median last frost date, April 10. NOAA Climate Normals 1991-2020
  14. Colorado State University Extension's vegetable planting guide groups cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon as very tender vegetables. Its rule for planting them: typically 2 or more weeks after the average last spring frost. CSU Extension GardenNotes #720
  15. GardenFacts calculation for Chicago: taking the NOAA median (50%) last frost date as the average last frost and applying the CSU rule for very tender vegetables, two weeks after the median last frost (April 10) is April 24. NOAA Climate Normals 1991-2020
  16. 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
  17. CSU Extension vegetable table: soil temperature, depth, spacing, days to harvest (table on this page). CSU Extension GardenNotes #720
  18. 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
  19. Chicago, Illinois overlaps 40 ZIP code areas. By land area, 89% in zone 6a, 11% in zone 6b. 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.