Last spring frost
May 13
Frost Dates for Napoleon, ND
First fall frost
Sep 28
Growing season
136 days
Hardiness zone
4a
In an average year around Napoleon, ND, the last spring frost (32°F) is about May 13 and the first fall frost is about Sep 28, giving roughly a 136-day growing season. To be safe most years, wait until May 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) | Jun 4 | May 23 | May 10 |
| Freeze (32°F) | May 26 | May 13 | May 1 |
| Hard (28°F) | May 16 | May 4 | Apr 20 |
| Severe (24°F) | May 9 | Apr 24 | Apr 10 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 4 | May 31 | May 28 | May 25 | May 23 | May 20 | May 17 | May 15 | May 10 |
| 32°F | May 26 | May 22 | May 18 | May 16 | May 13 | May 11 | May 8 | May 5 | May 1 |
| 28°F | May 16 | May 13 | May 9 | May 6 | May 4 | May 1 | Apr 30 | Apr 25 | Apr 20 |
| 24°F | May 9 | May 4 | May 1 | Apr 28 | Apr 24 | Apr 21 | Apr 18 | Apr 14 | Apr 10 |
| 20°F | May 1 | Apr 25 | Apr 21 | Apr 18 | Apr 16 | Apr 13 | Apr 10 | Apr 6 | Apr 1 |
| 16°F | Apr 21 | Apr 17 | Apr 13 | Apr 10 | Apr 7 | Apr 4 | Apr 1 | Mar 29 | Mar 22 |
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 7 | Sep 19 | Oct 1 |
| Freeze (32°F) | Sep 15 | Sep 28 | Oct 11 |
| Hard (28°F) | Sep 24 | Oct 6 | Oct 20 |
| Severe (24°F) | Oct 3 | Oct 16 | Oct 29 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 7 | Sep 11 | Sep 14 | Sep 17 | Sep 19 | Sep 22 | Sep 24 | Sep 27 | Oct 1 |
| 32°F | Sep 15 | Sep 19 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 11 |
| 28°F | Sep 24 | Sep 29 | Oct 1 | Oct 4 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 20 |
| 24°F | Oct 3 | Oct 6 | Oct 10 | Oct 13 | Oct 16 | Oct 19 | Oct 22 | Oct 25 | Oct 29 |
| 20°F | Oct 11 | Oct 16 | Oct 20 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 8 |
| 16°F | Oct 20 | Oct 26 | Oct 29 | Nov 1 | Nov 3 | Nov 5 | Nov 8 | Nov 12 | Nov 17 |
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: Napoleon, Nd, about 5.1 miles away@if(!empty($station['elevation_ft'])), at 1,980 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 Napoleon, ND?
On average, the last spring frost (32°F) around Napoleon, ND is about May 13. In cooler years it can run later, so for a safer bet many gardeners wait until May 1.
When is the first frost in the fall?
The first fall frost around Napoleon, ND typically arrives about Sep 28. 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 13 on average, or May 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 136 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 58561 Planting calendar → North Dakota frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026