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Frost dates and planting calendar for Naperville, Illinois

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 19[2]
Median first fall frost
Oct 23[3]
Growing season, median
185 days[4]

Naperville is in USDA hardiness zone 5b on the 2023 map[1]. The median last spring frost is April 19, which means in half of years the last frost comes after that date[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Apr 5, half of years Apr 19, 1 in 10 years after May 4Last frostmedian Apr 19First fall frost: 9 in 10 years before Nov 3, half of years Oct 23, 1 in 10 years before Oct 9First frostmedian Oct 23Frost riskHardyHardy vegetables: plant Mar 22 to Apr 5Mar 22 to Apr 5Semi-hardySemi-hardy vegetables: plant Apr 5 to Apr 19Apr 5 to Apr 19TenderTender vegetables: plant around Apr 19around Apr 19Very tenderVery tender vegetables: plant from May 3from May 3
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 are odds from NOAA records for 1991 to 2020, not a forecast[5]. They come from the Aurora weather station, which is near Naperville[5]. In 9 of 10 years the last spring frost comes after April 5, and in 1 of 10 years it comes after May 4[2]. In half of years the first fall frost comes before October 23, and in 1 of 10 years it comes before October 9[3]. Any year can be earlier or later than these dates.

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after April 5 after April 19 after May 4
First fall frost (32°F)[3] before October 9 before October 23 before November 3
  • Hard freeze (28°F): median last spring date April 8, median first fall date November 2[7].
  • Frost-free growing season: at least 164 days in 9 of 10 years, 185 days in half of years and 205 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: Aurora (USC00110338), 7.9 miles from the city center, 660 feet, 28 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 math and not local advice[6]. Hardy vegetables like broccoli, lettuce, peas and spinach can go in as early as 2 to 4 weeks before the median last frost, which works out to March 22 to April 5[6]. Semi-hardy vegetables like carrots, beets and potatoes can go in as early as 2 weeks before it, from April 5 up to the median date itself[9]. Tender vegetables like snap beans, sweet corn and cucumbers can start from seed around April 19[10]. Very tender vegetables like tomatoes, peppers and eggplant typically wait 2 or more weeks after the median last frost, and May 3 is the earliest start[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (April 19) is March 22 to April 5[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (April 19) is April 5, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, April 19[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (April 19), is May 3[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Mar 22 May 26 (from transplants)
Cabbage (hardy)[12] Mar 22 Jun 15 (from transplants)
Kohlrabi (hardy)[12] Mar 22 May 11
Lettuce (hardy)[12] Mar 22 May 21
Onions (hardy)[12] Mar 22 Jul 10
Peas (hardy)[12] Mar 22 May 26
Radishes (hardy)[12] Mar 22 Apr 21
Spinach (hardy)[12] Mar 22 May 1
Turnips (hardy)[12] Mar 22 May 11
Beets (semi-hardy)[12] Apr 5 Jun 4
Carrots (semi-hardy)[12] Apr 5 Jun 14
Cauliflower (semi-hardy)[12] Apr 5 not listed
Parsnips (semi-hardy)[12] Apr 5 Jun 14
Potatoes (semi-hardy)[12] Apr 5 Aug 8
Swiss chard (semi-hardy)[12] Apr 5 Jun 4
Snap beans (tender)[12] Apr 19 Jun 18
Sweet corn (tender)[12] Apr 19 Jun 18
Cucumbers (tender)[12] Apr 19 Jun 13
Summer squash (tender)[12] Apr 19 Jun 8
Cantaloupe (very tender)[12] May 3 Jul 27
Eggplant (very tender)[12] May 3 Jul 2 (from transplants)
Peppers (very tender)[12] May 3 Jul 12 (from transplants)
Tomatoes (very tender)[12] May 3 Jul 7 (from transplants)
Winter squash (very tender)[12] May 3 Aug 11
Watermelon (very tender)[12] May 3 Jul 27
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

A zone describes the average coldest night of the winter from 1991 to 2020, not summer heat or frost dates[14]. Zone 5b means an average yearly extreme low of -15°F to -10°F[1]. Naperville is not all one zone. By land area, 77% lies in ZIP code areas rated zone 5b and 23% lies in areas rated zone 6a[15].

Zone 5b: average annual extreme minimum temperature -15°F to -10°F (1991 to 2020)[1]. Modeled value at the city center: -10.3°F[1].

Share of the city's land area by ZIP code zone: zone 5b 77%, zone 6a 23%[15].

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

Zone by ZIP code
ZIP code Zone Coldest night range
60540[15] 5b -15 to -10°F
60564[15] 5b -15 to -10°F
60563[15] 5b -15 to -10°F
60565[15] 6a -10 to -5°F
60440[15] 6a -10 to -5°F
60504[15] 5b -15 to -10°F
60532[15] 5b -15 to -10°F
60585[15] 5b -15 to -10°F
60555[15] 5b -15 to -10°F

Questions people ask

What growing zone is Naperville?
The center of Naperville is in USDA zone 5b on the 2023 map[1]. By land area, 23% of the city is in ZIP code areas rated zone 6a[15].
When is the last frost in Naperville?
The median last spring frost is April 19, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after May 4[2].
When is the first frost in Naperville?
The median first fall frost is October 23, so in half of years the first frost comes before that date[3]. In 1 of 10 years it comes before October 9[3].
When to plant tomatoes in Naperville?
CSU Extension typically says very tender crops like tomatoes wait 2 or more weeks after the average last frost[11]. For Naperville that earliest start is May 3[11].
How long is the growing season in Naperville?
The growing season is at least 185 days in half of years[4]. It is at least 164 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Naperville, Illinois 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 10.3°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 5, in half of years after April 19, and in 1 of 10 years after May 4 (NOAA 1991 to 2020 normals). The median last frost date is April 19. 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 9, in half of years before October 23, and in 9 of 10 years before November 3 (NOAA 1991 to 2020 normals). The median first frost date is October 23. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 164 days in 9 of 10 years, at least 185 days in half of years, and at least 205 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Aurora weather station (USC00110338), 7.9 miles from the center of Naperville at 660 feet, using 28 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 8 and the median first fall date is November 2. 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. Naperville, Illinois overlaps 9 ZIP code areas. By land area, 77% lies in ZIP code areas rated zone 5b, 23% lies in ZIP code areas rated zone 6a. 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.