Last spring frost
Mar 18
Frost Dates for Lake Oswego, OR
First fall frost
Nov 18
Growing season
244 days
Hardiness zone
9a
In an average year around Lake Oswego, OR, the last spring frost (32°F) is about Mar 18 and the first fall frost is about Nov 18, giving roughly a 244-day growing season. To be safe most years, wait until Feb 19 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) | May 4 | Apr 15 | Mar 26 |
| Freeze (32°F) | Apr 11 | Mar 18 | Feb 19 |
| Hard (28°F) | Mar 7 | Feb 12 | Jan 1 |
| Severe (24°F) | Feb 21 | Jan 16 | Dec 12 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 4 | Apr 30 | Apr 26 | Apr 19 | Apr 15 | Apr 11 | Apr 5 | Apr 1 | Mar 26 |
| 32°F | Apr 11 | Apr 1 | Mar 27 | Mar 23 | Mar 18 | Mar 12 | Mar 5 | Feb 27 | Feb 19 |
| 28°F | Mar 7 | Feb 28 | Feb 23 | Feb 18 | Feb 12 | Feb 4 | Jan 27 | Jan 14 | Jan 1 |
| 24°F | Feb 21 | Feb 12 | Feb 2 | Jan 26 | Jan 16 | Jan 8 | Jan 2 | Dec 23 | Dec 12 |
| 20°F | Feb 16 | Feb 1 | Jan 19 | Jan 9 | Jan 3 | Dec 30 | Dec 23 | Dec 15 | Dec 3 |
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) | Oct 16 | Oct 31 | Nov 20 |
| Freeze (32°F) | Oct 30 | Nov 18 | Dec 12 |
| Hard (28°F) | Nov 16 | Dec 8 | Jan 5 |
| Severe (24°F) | Nov 29 | Dec 26 | Feb 4 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 16 | Oct 21 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 7 | Nov 13 | Nov 20 |
| 32°F | Oct 30 | Nov 4 | Nov 9 | Nov 13 | Nov 18 | Nov 22 | Nov 28 | Dec 3 | Dec 12 |
| 28°F | Nov 16 | Nov 24 | Nov 30 | Dec 3 | Dec 8 | Dec 13 | Dec 18 | Dec 26 | Jan 5 |
| 24°F | Nov 29 | Dec 6 | Dec 13 | Dec 19 | Dec 26 | Jan 1 | Jan 6 | Jan 17 | Feb 4 |
| 20°F | Dec 1 | Dec 6 | Dec 13 | Dec 21 | Dec 28 | Jan 3 | Jan 11 | Jan 26 | Feb 8 |
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: Oregon City, Or, about 5.4 miles away@if(!empty($station['elevation_ft'])), at 167 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 Lake Oswego, OR?
On average, the last spring frost (32°F) around Lake Oswego, OR is about Mar 18. In cooler years it can run later, so for a safer bet many gardeners wait until Feb 19.
When is the first frost in the fall?
The first fall frost around Lake Oswego, OR typically arrives about Nov 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 Mar 18 on average, or Feb 19 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 244 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 97034 Planting calendar → Oregon frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026