Last spring frost
Apr 16
Frost Dates for Flanagan, IL
First fall frost
Oct 24
Growing season
191 days
Hardiness zone
5b
In an average year around Flanagan, IL, the last spring frost (32°F) is about Apr 16 and the first fall frost is about Oct 24, giving roughly a 191-day growing season. To be safe most years, wait until Apr 3 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | May 11 | Apr 26 | Apr 13 |
| Freeze (32°F) | May 2 | Apr 16 | Apr 3 |
| Hard (28°F) | Apr 19 | Apr 4 | Mar 20 |
| Severe (24°F) | Apr 9 | Mar 26 | Mar 9 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 11 | May 6 | May 3 | Apr 30 | Apr 26 | Apr 23 | Apr 20 | Apr 17 | Apr 13 |
| 32°F | May 2 | Apr 26 | Apr 22 | Apr 19 | Apr 16 | Apr 13 | Apr 10 | Apr 7 | Apr 3 |
| 28°F | Apr 19 | Apr 14 | Apr 10 | Apr 7 | Apr 4 | Apr 2 | Apr 1 | Mar 28 | Mar 20 |
| 24°F | Apr 9 | Apr 4 | Apr 1 | Mar 30 | Mar 26 | Mar 23 | Mar 19 | Mar 15 | Mar 9 |
| 20°F | Mar 31 | Mar 27 | Mar 22 | Mar 18 | Mar 15 | Mar 11 | Mar 9 | Mar 4 | Feb 27 |
| 16°F | Mar 23 | Mar 17 | Mar 14 | Mar 11 | Mar 7 | Mar 4 | Mar 1 | Feb 24 | Feb 17 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Oct 2 | Oct 15 | Oct 27 |
| Freeze (32°F) | Oct 12 | Oct 24 | Nov 5 |
| Hard (28°F) | Oct 23 | Nov 3 | Nov 18 |
| Severe (24°F) | Nov 1 | Nov 14 | Nov 29 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 2 | Oct 6 | Oct 10 | Oct 12 | Oct 15 | Oct 17 | Oct 20 | Oct 23 | Oct 27 |
| 32°F | Oct 12 | Oct 17 | Oct 20 | Oct 22 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 5 |
| 28°F | Oct 23 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 6 | Nov 9 | Nov 13 | Nov 18 |
| 24°F | Nov 1 | Nov 5 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 21 | Nov 24 | Nov 29 |
| 20°F | Nov 8 | Nov 13 | Nov 17 | Nov 21 | Nov 24 | Nov 27 | Dec 1 | Dec 5 | Dec 11 |
| 16°F | Nov 14 | Nov 21 | Nov 25 | Nov 29 | Dec 2 | Dec 5 | Dec 9 | Dec 15 | Dec 20 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Pontiac, Il, about 7.6 miles away@if(!empty($station['elevation_ft'])), at 650 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Flanagan, IL?
On average, the last spring frost (32°F) around Flanagan, IL is about Apr 16. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 3.
When is the first frost in the fall?
The first fall frost around Flanagan, IL typically arrives about Oct 24. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around Apr 16 on average, or Apr 3 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 191 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 61743 Planting calendar → Illinois frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026