Chicago, Illinois Frost Dates, Growing Season & Hardiness Zone

When is the last frost in Chicago?

The typical last 32°F night is Apr 10, and in 1 year out of 10 a freeze still comes after Apr 25. Cold 36°F nights (frost possible on plants) typically last longer, to around Apr 23. The last hard freeze (28°F) typically comes earlier, around Apr 1.

Frost risk in Chicago drags on well past the typical date. The safer 1-in-10 date (Apr 25) is 15 days later than the typical Apr 10, so protect tender plants set out early on cold nights.

The typical last 36°F night (frost possible on plants in low spots) comes around Apr 23, 13 days after the typical last 32°F night. On clear, calm nights, frost can form on leaves even when the thermometer reads above freezing.

Of the 9 eligible stations near Chicago, ours has the earliest typical last frost. In a colder pocket, plan closer to Apr 25.

Is it too early to plant in Chicago?

Before Apr 10 the odds of another 32°F night are better than even; after Apr 25 they are about 1 in 10 or less.

Today's risk is computed in your browser from the same NOAA probability table, shown as the range between the two nearest NOAA probability levels.

When is the first frost in Chicago?

Half of years get their first 32°F night by Nov 5. In 1 year out of 10, it arrives as early as Oct 24. The first 36°F night (frost possible on plants) typically comes around Oct 26, and the first 28°F hard freeze around Nov 15.

Fall plantings are timed backward from first frost: Nov 5 typically, or Oct 24 if you want a cushion. See the planting calendar for each crop's date.

How long is Chicago's growing season?

In a typical year, Chicago gets 208 days between the last and first 32°F nights. About 1 year in 10, the season is shorter than 187 days.

A season this long fits most warm-season vegetables planted on time. Long-season crops do best when started from transplants.

Growing degree days measure the heat available for crops to grow. The station averages 3,106 a year (base 50°F).

How does Chicago's season compare?

Compared with the 56 U.S. cities with frost dates on this site, this typical frost-free season is longer than in 26 and shorter than in 29.

Growing degree days (base 50°F)

Annual normal: 3,106 GDD (NOAA flag R, 13 years). Running total by the end of each month (sum of NOAA daily GDD normals, so the year-end total can differ slightly from the annual normal):

What growing zone is Chicago? (USDA 2023)

On the 2023 USDA map, Chicago is zone 6a–6b (-10 to 0°F average coldest winter night). On the 2012 map, most of the city was 6a. Of the 53 city ZIPs listed in both tables, 21 moved up half a zone.

Zones: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 2026-10-08. Shown as published in the ZIP tables; this page does not show a zone map. Not the official USDA Plant Hardiness Zone Map (official map: planthardiness.ars.usda.gov).

Does the new zone change Chicago's frost dates?

No. Hardiness zones are based only on the average coldest winter temperature. They say nothing about when spring and fall frosts happen. Chicago's frost dates come from NOAA's 1991–2020 frost probabilities, which did not change with the 2023 zone map. Use your zone to pick perennials that will survive winter, and your frost dates to time planting.

Why do Chicago frost dates differ between websites?

If you've seen Apr 17 listed as Chicago's last frost date, that's the 30%-risk date: about 3 years in 10 still get a 32°F night after it. We lead with Apr 10, the 50% (median) date.

The 'safer' date, Apr 25, is the 10%-risk date. A 32°F night after it happens in only about 1 year in 10.

You may also see Apr 23. That's the 50% date for a 36°F night (frost possible on plants) rather than a 32°F freeze, so sites using 36°F as their cutoff list later dates.

The choice of weather station matters too. The 9 stations within 25 miles of the city center that pass our quality rules give typical (50%) last 32°F frost dates from Apr 10 to Apr 28; see the table below.

Which weather station is this based on?

Station

Chicago Northerly Island (NOAA USC00111550, COOP)

Distance

4.1 mi ENE of the city center

Elevation

583 ft; city center 594 ft (USGS), difference −11 ft

Record

NOAA completeness flag R, 15 of 30 years (1991–2020)

Confidence

Medium (rule)

Confidence: Medium. The station meets our quality rules, but its distance (4.1 mi) or elevation difference (−11 ft) is larger than ideal. Its frost statistics: NOAA flag R, 15 of 30 years.

Caveat: NOAA flags this station's frost statistics 'R' (representative). They rest on 15 of the 30 years in 1991–2020, with missing months filled in from surrounding stations. The nearest station with a full 'S' (standard) record is Chicago Midway Airport 3 SW, 8.4 mi away; its typical last frost is Apr 10.

Chicago planting dates at a glance

Balanced dates use the 30%-risk last-frost date as the anchor. The Chicago planting calendar has typical and safe dates, fall planting and a month-by-month list for 26 vegetables.

When to plant tomatoes in Chicago · Fall planting dates for Chicago

Frost dates near Chicago

All Illinois cities

Frequently asked questions

What is the average last frost date in Chicago?

The typical (median, 50%) last 32°F night in Chicago is Apr 10, based on NOAA 1991–2020 normals at Chicago Northerly Island. For a safer target, use Apr 25; after that, only about 1 year in 10 still has a freeze.

When is the first frost in Chicago?

Typically by Nov 5 for the first 32°F night, though about 1 year in 10 it comes as early as Oct 24. The first 36°F night (frost possible on plants) typically shows up around Oct 26.

What growing zone is Chicago, Illinois?

Chicago is in USDA hardiness zone 6a–6b on the 2023 map. Most of the city was already 6a on the 2012 map, though 21 of 53 city ZIPs changed zone.

Is it too early to plant in Chicago?

For frost-tender plants, yes if it's before Apr 10: until then, the odds of another 32°F night are better than even. Between Apr 10 and Apr 25, the risk falls from 50% to 10%. Cool-season crops like peas and lettuce can go in weeks earlier; see the planting calendar.

What temperature is a killing frost?

A light frost is enough to kill tender crops such as tomatoes. CSU Extension describes 28–32°F as a light frost and anything below 28°F as a heavy frost. We report NOAA odds at three thresholds: 36°F (frost possible on plants), 32°F (freeze, our headline) and 28°F (hard freeze).

Is first frost the same as first freeze?

Not quite. A freeze is when the air reaches 32°F. Frost is ice that forms on surfaces, and on calm, clear nights it can form with the air a few degrees above freezing. So in Chicago, the first 36°F night (frost possible on plants) typically comes around Oct 26, before the first 32°F night (Nov 5).

Download & sources

• Add Chicago frost & planting dates to your calendar (.ics, 2027)
• Printable planting calendar (PDF)
• How these numbers are calculated

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal and daily normals, station USC00111550); USDA Plant Hardiness Zone ZIP tables 2023 and 2012 by the PRISM Group, Oregon State University; Census 2020 ZIP/place relationship file; USGS elevation. Long-term odds, not a forecast. Figures and sentences are generated from these data by fixed rules; see the methodology. Last updated 2026-10-08.