Last spring frost
May 6
Frost Dates for Fort Thompson, SD
First fall frost
Oct 5
Growing season
152 days
Hardiness zone
4b
In an average year around Fort Thompson, SD, the last spring frost (32°F) is about May 6 and the first fall frost is about Oct 5, giving roughly a 152-day growing season. To be safe most years, wait until Apr 25 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 30 | May 16 | May 4 |
| Freeze (32°F) | May 20 | May 6 | Apr 25 |
| Hard (28°F) | May 10 | Apr 28 | Apr 13 |
| Severe (24°F) | May 2 | Apr 17 | Apr 4 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 30 | May 25 | May 22 | May 18 | May 16 | May 13 | May 11 | May 8 | May 4 |
| 32°F | May 20 | May 15 | May 11 | May 9 | May 6 | May 4 | May 2 | Apr 30 | Apr 25 |
| 28°F | May 10 | May 5 | May 3 | Apr 30 | Apr 28 | Apr 25 | Apr 22 | Apr 18 | Apr 13 |
| 24°F | May 2 | Apr 27 | Apr 24 | Apr 20 | Apr 17 | Apr 14 | Apr 12 | Apr 8 | Apr 4 |
| 20°F | Apr 23 | Apr 18 | Apr 14 | Apr 11 | Apr 7 | Apr 4 | Apr 2 | Mar 30 | Mar 22 |
| 16°F | Apr 15 | Apr 8 | Apr 4 | Apr 1 | Mar 31 | Mar 27 | Mar 22 | Mar 18 | Mar 12 |
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 17 | Sep 28 | Oct 11 |
| Freeze (32°F) | Sep 23 | Oct 5 | Oct 18 |
| Hard (28°F) | Oct 1 | Oct 16 | Oct 30 |
| Severe (24°F) | Oct 10 | Oct 24 | Nov 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 17 | Sep 20 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 11 |
| 32°F | Sep 23 | Sep 28 | Oct 1 | Oct 2 | Oct 5 | Oct 8 | Oct 11 | Oct 14 | Oct 18 |
| 28°F | Oct 1 | Oct 5 | Oct 10 | Oct 13 | Oct 16 | Oct 19 | Oct 21 | Oct 24 | Oct 30 |
| 24°F | Oct 10 | Oct 16 | Oct 19 | Oct 22 | Oct 24 | Oct 28 | Oct 31 | Nov 3 | Nov 7 |
| 20°F | Oct 19 | Oct 24 | Oct 28 | Oct 31 | Nov 2 | Nov 5 | Nov 9 | Nov 13 | Nov 18 |
| 16°F | Oct 27 | Nov 1 | Nov 5 | Nov 8 | Nov 12 | Nov 15 | Nov 18 | Nov 21 | Nov 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: Lake Sharpe Prj, Sd, about 4.3 miles away@if(!empty($station['elevation_ft'])), at 1,461 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 Fort Thompson, SD?
On average, the last spring frost (32°F) around Fort Thompson, SD is about May 6. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 25.
When is the first frost in the fall?
The first fall frost around Fort Thompson, SD typically arrives about Oct 5. 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 6 on average, or Apr 25 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 152 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 57339 Planting calendar → South Dakota frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026