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Frost dates and planting calendar for Rockford, 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 24[2]
Median first fall frost
Oct 17[3]
Growing season, median
174 days[4]

The center of Rockford, Illinois is in USDA hardiness zone 5b[1]. The median last spring frost is April 24, which means that in half of years the last frost comes after that date[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Apr 10, half of years Apr 24, 1 in 10 years after May 8Last frostmedian Apr 24First fall frost: 9 in 10 years before Oct 30, half of years Oct 17, 1 in 10 years before Oct 2First frostmedian Oct 17Frost riskHardyHardy vegetables: plant Mar 27 to Apr 10Mar 27 to Apr 10Semi-hardySemi-hardy vegetables: plant Apr 10 to Apr 24Apr 10 to Apr 24TenderTender vegetables: plant around Apr 24around Apr 24Very tenderVery tender vegetables: plant from May 8from May 8
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 frost dates for Rockford come from the Rockford Gtr Rockford Airport weather station[5]. In 9 of 10 years the last spring frost comes after April 10, and in 1 of 10 years it comes after May 8[2]. For fall, the first frost comes before October 17 in half of years, and before October 30 in 9 of 10 years[3]. These are odds from 1991 to 2020 records, not a forecast, so any year can be earlier or later[2][3].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after April 10 after April 24 after May 8
First fall frost (32°F)[3] before October 2 before October 17 before October 30
  • Hard freeze (28°F): median last spring date April 13, median first fall date October 28[7].
  • Frost-free growing season: at least 154 days in 9 of 10 years, 174 days in half of years and 192 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: Rockford Gtr Rockford Airport (USW00094822), 4.8 miles from the city center, 730 feet, 30 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension groups vegetables by how well they handle cold, and its guide was written for Colorado[6]. GardenFacts used the NOAA median last frost of April 24 as the average last frost[6]. Hardy vegetables such as broccoli, lettuce, peas and spinach can go in as early as 2 to 4 weeks before that date, which is March 27 to April 10[6]. Very tender vegetables such as tomatoes, peppers and eggplant typically wait 2 or more weeks after it, and the earliest start is May 8[9]. Tender vegetables such as snap beans and sweet corn can be seeded around April 24[10].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (April 24) is March 27 to April 10[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (April 24) is April 10, up to the median date itself[11]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, April 24[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (April 24), is May 8[9]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Mar 27 May 31 (from transplants)
Cabbage (hardy)[12] Mar 27 Jun 20 (from transplants)
Kohlrabi (hardy)[12] Mar 27 May 16
Lettuce (hardy)[12] Mar 27 May 26
Onions (hardy)[12] Mar 27 Jul 15
Peas (hardy)[12] Mar 27 May 31
Radishes (hardy)[12] Mar 27 Apr 26
Spinach (hardy)[12] Mar 27 May 6
Turnips (hardy)[12] Mar 27 May 16
Beets (semi-hardy)[12] Apr 10 Jun 9
Carrots (semi-hardy)[12] Apr 10 Jun 19
Cauliflower (semi-hardy)[12] Apr 10 not listed
Parsnips (semi-hardy)[12] Apr 10 Jun 19
Potatoes (semi-hardy)[12] Apr 10 Aug 13
Swiss chard (semi-hardy)[12] Apr 10 Jun 9
Snap beans (tender)[12] Apr 24 Jun 23
Sweet corn (tender)[12] Apr 24 Jun 23
Cucumbers (tender)[12] Apr 24 Jun 18
Summer squash (tender)[12] Apr 24 Jun 13
Cantaloupe (very tender)[12] May 8 Aug 1
Eggplant (very tender)[12] May 8 Jul 7 (from transplants)
Peppers (very tender)[12] May 8 Jul 17 (from transplants)
Tomatoes (very tender)[12] May 8 Jul 12 (from transplants)
Winter squash (very tender)[12] May 8 Aug 16
Watermelon (very tender)[12] May 8 Aug 1
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 a typical winter falls between -15°F and -10°F, averaged over 1991 to 2020[1]. The zone is about winter lows. It does not describe summer heat or frost dates[14]. By land area, 100% of Rockford lies in ZIP code areas rated zone 5b, so the city is not split across zones[15].

Zone 5b: average annual extreme minimum temperature -15°F to -10°F (1991 to 2020)[1]. Modeled value at the city center: -13.4°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
61109[15] 5b -15 to -10°F
61107[15] 5b -15 to -10°F
61108[15] 5b -15 to -10°F
61101[15] 5b -15 to -10°F
61102[15] 5b -15 to -10°F
61114[15] 5b -15 to -10°F
61103[15] 5b -15 to -10°F
61104[15] 5b -15 to -10°F
61020[15] 5b -15 to -10°F
61111[15] 5b -15 to -10°F
61088[15] 5b -15 to -10°F

Questions people ask

What growing zone is Rockford, Illinois?
The 2023 USDA map puts the center of Rockford in zone 5b[1]. All of the city's land area is in ZIP code areas rated 5b[15].
When is the last frost in Rockford?
The median last spring frost at the airport station is April 24, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after May 8[2].
When is the first frost in Rockford?
The median first fall frost is October 17, so in half of years the first frost comes before that date[3]. In 1 of 10 years it comes before October 2[3].
When to plant tomatoes in Rockford?
CSU Extension groups tomatoes as very tender, typically 2 or more weeks after the average last spring frost[9]. Using the median last frost of April 24, the earliest start is May 8[9].
How long is the growing season in Rockford?
The growing season is at least 174 days in half of years[4]. It is at least 154 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Rockford, 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 13.4°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 10, in half of years after April 24, and in 1 of 10 years after May 8 (NOAA 1991 to 2020 normals). The median last frost date is April 24. 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 2, in half of years before October 17, and in 9 of 10 years before October 30 (NOAA 1991 to 2020 normals). The median first frost date is October 17. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 154 days in 9 of 10 years, at least 174 days in half of years, and at least 192 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Rockford Gtr Rockford Airport weather station (USW00094822), 4.8 miles from the center of Rockford at 730 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 13 and the median first fall date is October 28. 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 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
  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 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
  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. Rockford, Illinois overlaps 11 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.