Last spring frost
May 28
Frost Dates for Mount Vernon, OR
First fall frost
Sep 18
Growing season
113 days
Hardiness zone
6b
In an average year around Mount Vernon, OR, the last spring frost (32°F) is about May 28 and the first fall frost is about Sep 18, giving roughly a 113-day growing season. To be safe most years, wait until May 12 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 8 | Jun 19 | May 31 |
| Freeze (32°F) | Jun 15 | May 28 | May 12 |
| Hard (28°F) | May 24 | May 8 | Apr 25 |
| Severe (24°F) | May 7 | Apr 23 | Apr 3 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 8 | Jun 29 | Jun 26 | Jun 22 | Jun 19 | Jun 15 | Jun 11 | Jun 6 | May 31 |
| 32°F | Jun 15 | Jun 8 | Jun 4 | May 31 | May 28 | May 24 | May 20 | May 16 | May 12 |
| 28°F | May 24 | May 18 | May 13 | May 11 | May 8 | May 4 | May 2 | Apr 30 | Apr 25 |
| 24°F | May 7 | May 2 | Apr 30 | Apr 27 | Apr 23 | Apr 19 | Apr 15 | Apr 11 | Apr 3 |
| 20°F | Apr 22 | Apr 13 | Apr 8 | Apr 4 | Mar 31 | Mar 27 | Mar 21 | Mar 15 | Mar 8 |
| 16°F | Mar 30 | Mar 20 | Mar 14 | Mar 9 | Mar 4 | Feb 28 | Feb 24 | Feb 18 | Feb 11 |
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) | Aug 16 | Sep 2 | Sep 20 |
| Freeze (32°F) | Sep 2 | Sep 18 | Oct 4 |
| Hard (28°F) | Sep 13 | Oct 1 | Oct 16 |
| Severe (24°F) | Sep 27 | Oct 13 | Nov 2 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 16 | Aug 23 | Aug 28 | Aug 31 | Sep 2 | Sep 5 | Sep 9 | Sep 13 | Sep 20 |
| 32°F | Sep 2 | Sep 7 | Sep 11 | Sep 15 | Sep 18 | Sep 21 | Sep 24 | Sep 29 | Oct 4 |
| 28°F | Sep 13 | Sep 19 | Sep 23 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 10 | Oct 16 |
| 24°F | Sep 27 | Oct 3 | Oct 6 | Oct 10 | Oct 13 | Oct 17 | Oct 20 | Oct 26 | Nov 2 |
| 20°F | Oct 11 | Oct 17 | Oct 21 | Oct 26 | Oct 29 | Nov 1 | Nov 8 | Nov 14 | Nov 21 |
| 16°F | Oct 22 | Oct 29 | Nov 2 | Nov 9 | Nov 14 | Nov 19 | Nov 23 | Nov 28 | Dec 4 |
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: John Day, Or, about 11.2 miles away@if(!empty($station['elevation_ft'])), at 3,063 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 Mount Vernon, OR?
On average, the last spring frost (32°F) around Mount Vernon, OR is about May 28. In cooler years it can run later, so for a safer bet many gardeners wait until May 12.
When is the first frost in the fall?
The first fall frost around Mount Vernon, OR typically arrives about Sep 18. 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 28 on average, or May 12 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 97865 Planting calendar → Oregon frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026