Last spring frost
May 7
Frost Dates for Mount Horeb, WI
First fall frost
Oct 1
Growing season
148 days
Hardiness zone
5a
In an average year around Mount Horeb, WI, the last spring frost (32°F) is about May 7 and the first fall frost is about Oct 1, giving roughly a 148-day growing season. To be safe most years, wait until Apr 22 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) | Jun 1 | May 18 | Apr 30 |
| Freeze (32°F) | May 22 | May 7 | Apr 22 |
| Hard (28°F) | May 13 | Apr 27 | Apr 12 |
| Severe (24°F) | May 3 | Apr 16 | Apr 2 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 1 | May 28 | May 24 | May 21 | May 18 | May 14 | May 11 | May 6 | Apr 30 |
| 32°F | May 22 | May 17 | May 13 | May 10 | May 7 | May 4 | Apr 30 | Apr 27 | Apr 22 |
| 28°F | May 13 | May 7 | May 3 | Apr 30 | Apr 27 | Apr 24 | Apr 20 | Apr 16 | Apr 12 |
| 24°F | May 3 | Apr 28 | Apr 23 | Apr 20 | Apr 16 | Apr 13 | Apr 10 | Apr 6 | Apr 2 |
| 20°F | Apr 22 | Apr 15 | Apr 10 | Apr 7 | Apr 5 | Apr 2 | Mar 31 | Mar 26 | Mar 20 |
| 16°F | Apr 9 | Apr 4 | Apr 1 | Mar 30 | Mar 26 | Mar 23 | Mar 19 | Mar 15 | Mar 10 |
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 11 | Sep 23 | Oct 6 |
| Freeze (32°F) | Sep 18 | Oct 1 | Oct 16 |
| Hard (28°F) | Sep 26 | Oct 12 | Oct 29 |
| Severe (24°F) | Oct 7 | Oct 24 | Nov 8 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 11 | Sep 15 | Sep 18 | Sep 21 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 6 |
| 32°F | Sep 18 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 16 |
| 28°F | Sep 26 | Oct 1 | Oct 4 | Oct 8 | Oct 12 | Oct 15 | Oct 18 | Oct 22 | Oct 29 |
| 24°F | Oct 7 | Oct 14 | Oct 18 | Oct 21 | Oct 24 | Oct 27 | Oct 30 | Nov 3 | Nov 8 |
| 20°F | Oct 21 | Oct 27 | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 12 | Nov 16 | Nov 20 |
| 16°F | Nov 2 | Nov 7 | Nov 11 | Nov 15 | Nov 17 | Nov 20 | Nov 23 | Nov 27 | Dec 1 |
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: Mazomanie Wwtp, Wi, about 14.9 miles away@if(!empty($station['elevation_ft'])), at 764 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 Mount Horeb, WI?
On average, the last spring frost (32°F) around Mount Horeb, WI is about May 7. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 22.
When is the first frost in the fall?
The first fall frost around Mount Horeb, WI typically arrives about Oct 1. 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 May 7 on average, or Apr 22 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 148 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 53572 Planting calendar → Wisconsin frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026