Last spring frost
May 4
Frost Dates for Boulder, UT
First fall frost
Oct 14
Growing season
160 days
Hardiness zone
7a
In an average year around Boulder, UT, the last spring frost (32°F) is about May 4 and the first fall frost is about Oct 14, giving roughly a 160-day growing season. To be safe most years, wait until Apr 20 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 6 | May 18 | May 1 |
| Freeze (32°F) | May 25 | May 4 | Apr 20 |
| Hard (28°F) | May 12 | Apr 23 | Apr 5 |
| Severe (24°F) | Apr 26 | Apr 8 | Mar 14 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 6 | May 31 | May 27 | May 22 | May 18 | May 14 | May 11 | May 6 | May 1 |
| 32°F | May 25 | May 17 | May 12 | May 7 | May 4 | Apr 30 | Apr 28 | Apr 25 | Apr 20 |
| 28°F | May 12 | May 3 | Apr 29 | Apr 26 | Apr 23 | Apr 19 | Apr 15 | Apr 11 | Apr 5 |
| 24°F | Apr 26 | Apr 20 | Apr 16 | Apr 12 | Apr 8 | Apr 4 | Mar 29 | Mar 22 | Mar 14 |
| 20°F | Apr 12 | Apr 4 | Mar 27 | Mar 21 | Mar 15 | Mar 11 | Mar 7 | Mar 2 | Feb 25 |
| 16°F | Mar 24 | Mar 12 | Mar 7 | Mar 3 | Feb 28 | Feb 23 | Feb 18 | Feb 13 | Feb 5 |
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 22 | Oct 5 | Oct 18 |
| Freeze (32°F) | Sep 30 | Oct 14 | Oct 29 |
| Hard (28°F) | Oct 7 | Oct 23 | Nov 9 |
| Severe (24°F) | Oct 18 | Nov 4 | Nov 20 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 22 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 7 | Oct 11 | Oct 14 | Oct 18 |
| 32°F | Sep 30 | Oct 4 | Oct 7 | Oct 11 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 29 |
| 28°F | Oct 7 | Oct 13 | Oct 17 | Oct 20 | Oct 23 | Oct 27 | Oct 30 | Nov 4 | Nov 9 |
| 24°F | Oct 18 | Oct 24 | Oct 28 | Nov 1 | Nov 4 | Nov 8 | Nov 12 | Nov 16 | Nov 20 |
| 20°F | Oct 27 | Nov 2 | Nov 7 | Nov 12 | Nov 16 | Nov 19 | Nov 22 | Nov 25 | Nov 30 |
| 16°F | Nov 5 | Nov 13 | Nov 18 | Nov 22 | Nov 25 | Nov 29 | Dec 2 | Dec 6 | Dec 12 |
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: Boulder, Ut, about 3 miles away@if(!empty($station['elevation_ft'])), at 6,650 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 Boulder, UT?
On average, the last spring frost (32°F) around Boulder, UT is about May 4. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 20.
When is the first frost in the fall?
The first fall frost around Boulder, UT typically arrives about Oct 14. 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 4 on average, or Apr 20 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 160 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 84716 Planting calendar → Utah frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026