Last spring frost
Apr 11
Frost Dates for Humboldt, IL
First fall frost
Oct 29
Growing season
199 days
Hardiness zone
6a
In an average year around Humboldt, IL, the last spring frost (32°F) is about Apr 11 and the first fall frost is about Oct 29, giving roughly a 199-day growing season. To be safe most years, wait until Mar 31 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 9 | Apr 23 | Apr 9 |
| Freeze (32°F) | Apr 28 | Apr 11 | Mar 31 |
| Hard (28°F) | Apr 17 | Apr 2 | Mar 15 |
| Severe (24°F) | Apr 6 | Mar 22 | Mar 5 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 9 | May 4 | Apr 30 | Apr 26 | Apr 23 | Apr 20 | Apr 18 | Apr 14 | Apr 9 |
| 32°F | Apr 28 | Apr 22 | Apr 18 | Apr 15 | Apr 11 | Apr 9 | Apr 6 | Apr 3 | Mar 31 |
| 28°F | Apr 17 | Apr 10 | Apr 6 | Apr 4 | Apr 2 | Mar 31 | Mar 27 | Mar 22 | Mar 15 |
| 24°F | Apr 6 | Apr 2 | Mar 30 | Mar 26 | Mar 22 | Mar 18 | Mar 15 | Mar 11 | Mar 5 |
| 20°F | Mar 29 | Mar 23 | Mar 18 | Mar 15 | Mar 12 | Mar 9 | Mar 5 | Mar 2 | Feb 23 |
| 16°F | Mar 19 | Mar 14 | Mar 10 | Mar 6 | Mar 4 | Mar 1 | Feb 25 | Feb 19 | Feb 9 |
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 19 | Oct 30 |
| Freeze (32°F) | Oct 15 | Oct 29 | Nov 9 |
| Hard (28°F) | Oct 28 | Nov 7 | Nov 21 |
| Severe (24°F) | Nov 4 | Nov 17 | Dec 2 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 2 | Oct 9 | Oct 13 | Oct 15 | Oct 19 | Oct 21 | Oct 24 | Oct 27 | Oct 30 |
| 32°F | Oct 15 | Oct 20 | Oct 24 | Oct 27 | Oct 29 | Oct 31 | Nov 1 | Nov 5 | Nov 9 |
| 28°F | Oct 28 | Oct 31 | Nov 2 | Nov 4 | Nov 7 | Nov 10 | Nov 13 | Nov 17 | Nov 21 |
| 24°F | Nov 4 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 20 | Nov 23 | Nov 27 | Dec 2 |
| 20°F | Nov 10 | Nov 14 | Nov 18 | Nov 22 | Nov 26 | Nov 30 | Dec 4 | Dec 8 | Dec 15 |
| 16°F | Nov 16 | Nov 23 | Nov 28 | Dec 1 | Dec 6 | Dec 10 | Dec 15 | Dec 20 | Dec 25 |
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: Mattoon, Il, about 7.9 miles away@if(!empty($station['elevation_ft'])), at 701 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 Humboldt, IL?
On average, the last spring frost (32°F) around Humboldt, IL is about Apr 11. In cooler years it can run later, so for a safer bet many gardeners wait until Mar 31.
When is the first frost in the fall?
The first fall frost around Humboldt, IL typically arrives about Oct 29. 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 11 on average, or Mar 31 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 199 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 61931 Planting calendar → Illinois frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026