Last spring frost
Apr 13
Frost Dates for Watson, IL
First fall frost
Oct 24
Growing season
191 days
Hardiness zone
6b
In an average year around Watson, IL, the last spring frost (32°F) is about Apr 13 and the first fall frost is about Oct 24, giving roughly a 191-day growing season. To be safe most years, wait until Apr 1 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 24 | Apr 10 |
| Freeze (32°F) | Apr 29 | Apr 13 | Apr 1 |
| Hard (28°F) | Apr 17 | Apr 2 | Mar 17 |
| Severe (24°F) | Apr 7 | Mar 22 | Mar 4 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 11 | May 5 | Apr 30 | Apr 27 | Apr 24 | Apr 21 | Apr 18 | Apr 14 | Apr 10 |
| 32°F | Apr 29 | Apr 23 | Apr 19 | Apr 16 | Apr 13 | Apr 11 | Apr 7 | Apr 5 | Apr 1 |
| 28°F | Apr 17 | Apr 11 | Apr 7 | Apr 4 | Apr 2 | Mar 31 | Mar 27 | Mar 22 | Mar 17 |
| 24°F | Apr 7 | Apr 2 | Mar 30 | Mar 26 | Mar 22 | Mar 18 | Mar 15 | Mar 11 | Mar 4 |
| 20°F | Mar 29 | Mar 22 | Mar 18 | Mar 15 | Mar 12 | Mar 8 | Mar 4 | Feb 28 | Feb 22 |
| 16°F | Mar 19 | Mar 14 | Mar 10 | Mar 6 | Mar 3 | Feb 28 | Feb 24 | Feb 16 | 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) | Sep 29 | Oct 13 | Oct 25 |
| Freeze (32°F) | Oct 9 | Oct 24 | Nov 5 |
| Hard (28°F) | Oct 20 | Nov 1 | Nov 19 |
| Severe (24°F) | Nov 1 | Nov 13 | Dec 2 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 29 | Oct 3 | Oct 8 | Oct 11 | Oct 13 | Oct 16 | Oct 19 | Oct 22 | Oct 25 |
| 32°F | Oct 9 | Oct 15 | Oct 18 | Oct 22 | Oct 24 | Oct 26 | Oct 28 | Oct 31 | Nov 5 |
| 28°F | Oct 20 | Oct 25 | Oct 28 | Oct 31 | Nov 1 | Nov 4 | Nov 8 | Nov 11 | Nov 19 |
| 24°F | Nov 1 | Nov 3 | Nov 6 | Nov 10 | Nov 13 | Nov 17 | Nov 21 | Nov 28 | Dec 2 |
| 20°F | Nov 8 | Nov 13 | Nov 17 | Nov 21 | Nov 25 | Nov 30 | Dec 3 | Dec 7 | Dec 14 |
| 16°F | Nov 15 | Nov 23 | Nov 28 | Dec 1 | Dec 5 | Dec 10 | Dec 15 | Dec 19 | Dec 24 |
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: Effingham 3Sw, Il, about 7.3 miles away@if(!empty($station['elevation_ft'])), at 625 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 Watson, IL?
On average, the last spring frost (32°F) around Watson, IL is about Apr 13. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 1.
When is the first frost in the fall?
The first fall frost around Watson, 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 13 on average, or Apr 1 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 62473 Planting calendar → Illinois frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026