Last spring frost
May 18
Frost Dates for Brookston, MN
First fall frost
Oct 1
Growing season
135 days
Hardiness zone
4a
In an average year around Brookston, MN, the last spring frost (32°F) is about May 18 and the first fall frost is about Oct 1, giving roughly a 135-day growing season. To be safe most years, wait until May 2 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 17 | Jun 1 | May 16 |
| Freeze (32°F) | Jun 3 | May 18 | May 2 |
| Hard (28°F) | May 21 | May 4 | Apr 22 |
| Severe (24°F) | May 8 | Apr 25 | Apr 10 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 17 | Jun 11 | Jun 6 | Jun 3 | Jun 1 | May 30 | May 27 | May 23 | May 16 |
| 32°F | Jun 3 | May 30 | May 26 | May 22 | May 18 | May 15 | May 11 | May 7 | May 2 |
| 28°F | May 21 | May 16 | May 10 | May 7 | May 4 | May 1 | Apr 29 | Apr 26 | Apr 22 |
| 24°F | May 8 | May 2 | Apr 30 | Apr 28 | Apr 25 | Apr 22 | Apr 19 | Apr 15 | Apr 10 |
| 20°F | Apr 28 | Apr 23 | Apr 19 | Apr 16 | Apr 13 | Apr 10 | Apr 7 | Apr 4 | Apr 1 |
| 16°F | Apr 19 | Apr 14 | Apr 11 | Apr 8 | Apr 5 | Apr 3 | 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 8 | Sep 22 | Oct 4 |
| Freeze (32°F) | Sep 19 | Oct 1 | Oct 14 |
| Hard (28°F) | Sep 29 | Oct 12 | Oct 27 |
| Severe (24°F) | Oct 10 | Oct 25 | Nov 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 8 | Sep 14 | Sep 17 | Sep 20 | Sep 22 | Sep 24 | Sep 27 | Sep 30 | Oct 4 |
| 32°F | Sep 19 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 14 |
| 28°F | Sep 29 | Oct 2 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 19 | Oct 22 | Oct 27 |
| 24°F | Oct 10 | Oct 15 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 7 |
| 20°F | Oct 21 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 6 | Nov 8 | Nov 11 | Nov 16 |
| 16°F | Oct 31 | Nov 2 | Nov 6 | Nov 8 | Nov 11 | Nov 13 | Nov 15 | Nov 18 | Nov 23 |
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: Duluth Nws, Mn, about 12.3 miles away@if(!empty($station['elevation_ft'])), at 1,433 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 Brookston, MN?
On average, the last spring frost (32°F) around Brookston, MN is about May 18. In cooler years it can run later, so for a safer bet many gardeners wait until May 2.
When is the first frost in the fall?
The first fall frost around Brookston, MN 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 18 on average, or May 2 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 135 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 55779 Planting calendar → Minnesota frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026