Last spring frost
May 17
Frost Dates for Lewis, CO
First fall frost
Oct 9
Growing season
145 days
Hardiness zone
6b
In an average year around Lewis, CO, the last spring frost (32°F) is about May 17 and the first fall frost is about Oct 9, giving roughly a 145-day growing season. To be safe most years, wait until Apr 29 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 13 | May 30 | May 13 |
| Freeze (32°F) | Jun 4 | May 17 | Apr 29 |
| Hard (28°F) | May 22 | Apr 30 | Apr 13 |
| Severe (24°F) | May 6 | Apr 15 | Mar 25 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 13 | Jun 7 | Jun 4 | Jun 1 | May 30 | May 26 | May 22 | May 18 | May 13 |
| 32°F | Jun 4 | May 30 | May 24 | May 20 | May 17 | May 13 | May 8 | May 3 | Apr 29 |
| 28°F | May 22 | May 16 | May 9 | May 3 | Apr 30 | Apr 27 | Apr 23 | Apr 20 | Apr 13 |
| 24°F | May 6 | Apr 29 | Apr 24 | Apr 20 | Apr 15 | Apr 12 | Apr 7 | Apr 2 | Mar 25 |
| 20°F | Apr 22 | Apr 14 | Apr 7 | Apr 3 | Mar 30 | Mar 25 | Mar 18 | Mar 11 | Mar 5 |
| 16°F | Apr 3 | Mar 28 | Mar 19 | Mar 14 | Mar 9 | Mar 5 | Mar 1 | Feb 26 | Feb 17 |
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 15 | Sep 30 | Oct 14 |
| Freeze (32°F) | Sep 24 | Oct 9 | Oct 24 |
| Hard (28°F) | Oct 1 | Oct 19 | Nov 3 |
| Severe (24°F) | Oct 10 | Oct 30 | Nov 14 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 15 | Sep 21 | Sep 24 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 9 | Oct 14 |
| 32°F | Sep 24 | Sep 29 | Oct 2 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 20 | Oct 24 |
| 28°F | Oct 1 | Oct 6 | Oct 11 | Oct 15 | Oct 19 | Oct 22 | Oct 26 | Oct 29 | Nov 3 |
| 24°F | Oct 10 | Oct 17 | Oct 22 | Oct 27 | Oct 30 | Nov 2 | Nov 5 | Nov 9 | Nov 14 |
| 20°F | Oct 21 | Oct 28 | Nov 1 | Nov 5 | Nov 8 | Nov 12 | Nov 15 | Nov 19 | Nov 23 |
| 16°F | Oct 31 | Nov 7 | Nov 11 | Nov 15 | Nov 17 | Nov 20 | Nov 24 | Nov 27 | Dec 3 |
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: Yellow Jacket 2W, Co, about 2.5 miles away@if(!empty($station['elevation_ft'])), at 6,933 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 Lewis, CO?
On average, the last spring frost (32°F) around Lewis, CO is about May 17. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 29.
When is the first frost in the fall?
The first fall frost around Lewis, CO typically arrives about Oct 9. 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 17 on average, or Apr 29 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 145 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 81335 Planting calendar → Colorado frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026