Last spring frost
May 11
Frost Dates for Union, OR
First fall frost
Sep 26
Growing season
136 days
Hardiness zone
6b
In an average year around Union, OR, the last spring frost (32°F) is about May 11 and the first fall frost is about Sep 26, giving roughly a 136-day growing season. To be safe most years, wait until Apr 26 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 23 | Jun 2 | May 14 |
| Freeze (32°F) | May 31 | May 11 | Apr 26 |
| Hard (28°F) | May 10 | Apr 24 | Apr 7 |
| Severe (24°F) | Apr 22 | Apr 3 | Mar 12 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 23 | Jun 15 | Jun 10 | Jun 6 | Jun 2 | May 30 | May 26 | May 21 | May 14 |
| 32°F | May 31 | May 24 | May 19 | May 15 | May 11 | May 8 | May 4 | May 1 | Apr 26 |
| 28°F | May 10 | May 3 | Apr 30 | Apr 28 | Apr 24 | Apr 20 | Apr 17 | Apr 12 | Apr 7 |
| 24°F | Apr 22 | Apr 15 | Apr 10 | Apr 6 | Apr 3 | Mar 30 | Mar 26 | Mar 20 | Mar 12 |
| 20°F | Apr 3 | Mar 26 | Mar 19 | Mar 14 | Mar 10 | Mar 6 | Mar 2 | Feb 25 | Feb 16 |
| 16°F | Mar 8 | Mar 3 | Feb 28 | Feb 24 | Feb 20 | Feb 15 | Feb 10 | Feb 4 | Jan 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) | Aug 29 | Sep 10 | Sep 26 |
| Freeze (32°F) | Sep 9 | Sep 26 | Oct 10 |
| Hard (28°F) | Sep 23 | Oct 7 | Oct 23 |
| Severe (24°F) | Oct 3 | Oct 21 | Nov 11 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 29 | Sep 2 | Sep 5 | Sep 8 | Sep 10 | Sep 14 | Sep 17 | Sep 21 | Sep 26 |
| 32°F | Sep 9 | Sep 15 | Sep 20 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 5 | Oct 10 |
| 28°F | Sep 23 | Sep 29 | Oct 2 | Oct 5 | Oct 7 | Oct 11 | Oct 14 | Oct 18 | Oct 23 |
| 24°F | Oct 3 | Oct 8 | Oct 14 | Oct 17 | Oct 21 | Oct 25 | Oct 29 | Nov 2 | Nov 11 |
| 20°F | Oct 16 | Oct 22 | Oct 27 | Nov 1 | Nov 5 | Nov 10 | Nov 16 | Nov 24 | Nov 30 |
| 16°F | Oct 27 | Nov 2 | Nov 10 | Nov 17 | Nov 23 | Nov 28 | Dec 2 | Dec 9 | Dec 17 |
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: Union, Or, about 11.4 miles away@if(!empty($station['elevation_ft'])), at 2,777 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 Union, OR?
On average, the last spring frost (32°F) around Union, OR is about May 11. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 26.
When is the first frost in the fall?
The first fall frost around Union, OR typically arrives about Sep 26. 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 11 on average, or Apr 26 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 136 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 97883 Planting calendar → Oregon frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026