Last spring frost
Jun 2
Frost Dates for Aspen, CO
First fall frost
Sep 23
Growing season
113 days
Hardiness zone
5a
In an average year around Aspen, CO, the last spring frost (32°F) is about Jun 2 and the first fall frost is about Sep 23, giving roughly a 113-day growing season. To be safe most years, wait until May 17 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) | Jul 1 | Jun 16 | Jun 3 |
| Freeze (32°F) | Jun 17 | Jun 2 | May 17 |
| Hard (28°F) | Jun 5 | May 18 | May 3 |
| Severe (24°F) | May 23 | May 4 | Apr 20 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 1 | Jun 25 | Jun 22 | Jun 19 | Jun 16 | Jun 13 | Jun 10 | Jun 7 | Jun 3 |
| 32°F | Jun 17 | Jun 12 | Jun 8 | Jun 5 | Jun 2 | May 31 | May 27 | May 22 | May 17 |
| 28°F | Jun 5 | May 31 | May 26 | May 22 | May 18 | May 15 | May 11 | May 6 | May 3 |
| 24°F | May 23 | May 16 | May 12 | May 8 | May 4 | May 1 | Apr 28 | Apr 25 | Apr 20 |
| 20°F | May 9 | May 3 | Apr 30 | Apr 26 | Apr 22 | Apr 20 | Apr 16 | Apr 13 | Apr 8 |
| 16°F | Apr 27 | Apr 21 | Apr 17 | Apr 13 | Apr 9 | Apr 7 | Apr 4 | Mar 31 | Mar 24 |
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 1 | Sep 14 | Sep 25 |
| Freeze (32°F) | Sep 12 | Sep 23 | Oct 4 |
| Hard (28°F) | Sep 18 | Oct 1 | Oct 16 |
| Severe (24°F) | Sep 27 | Oct 10 | Oct 25 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 1 | Sep 5 | Sep 9 | Sep 12 | Sep 14 | Sep 16 | Sep 19 | Sep 21 | Sep 25 |
| 32°F | Sep 12 | Sep 16 | Sep 19 | Sep 21 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 4 |
| 28°F | Sep 18 | Sep 23 | Sep 27 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 16 |
| 24°F | Sep 27 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 13 | Oct 17 | Oct 20 | Oct 25 |
| 20°F | Oct 4 | Oct 9 | Oct 13 | Oct 17 | Oct 21 | Oct 23 | Oct 27 | Oct 31 | Nov 4 |
| 16°F | Oct 13 | Oct 18 | Oct 22 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 9 | Nov 15 |
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: Aspen 1Sw, Co, about 9.3 miles away@if(!empty($station['elevation_ft'])), at 8,175 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 Aspen, CO?
On average, the last spring frost (32°F) around Aspen, CO is about Jun 2. In cooler years it can run later, so for a safer bet many gardeners wait until May 17.
When is the first frost in the fall?
The first fall frost around Aspen, CO typically arrives about Sep 23. 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 Jun 2 on average, or May 17 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 113 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 81612 Planting calendar → Colorado frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026