Last spring frost
Apr 16
Frost Dates for Hillsboro, OR
First fall frost
Oct 23
Growing season
191 days
Hardiness zone
8b
In an average year around Hillsboro, OR, the last spring frost (32°F) is about Apr 16 and the first fall frost is about Oct 23, giving roughly a 191-day growing season. To be safe most years, wait until Mar 25 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 27 | May 5 | Apr 21 |
| Freeze (32°F) | May 3 | Apr 16 | Mar 25 |
| Hard (28°F) | Apr 9 | Mar 13 | Feb 15 |
| Severe (24°F) | Mar 5 | Feb 14 | Dec 31 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 27 | May 20 | May 14 | May 9 | May 5 | May 2 | Apr 30 | Apr 26 | Apr 21 |
| 32°F | May 3 | Apr 29 | Apr 25 | Apr 20 | Apr 16 | Apr 11 | Apr 5 | Mar 31 | Mar 25 |
| 28°F | Apr 9 | Mar 31 | Mar 24 | Mar 18 | Mar 13 | Mar 7 | Mar 1 | Feb 25 | Feb 15 |
| 24°F | Mar 5 | Feb 27 | Feb 23 | Feb 19 | Feb 14 | Feb 6 | Jan 28 | Jan 16 | Dec 31 |
| 20°F | Feb 20 | Feb 12 | Feb 1 | Jan 24 | Jan 9 | Dec 31 | Dec 22 | Dec 11 | Dec 1 |
| 16°F | Feb 10 | Jan 31 | Jan 15 | Jan 6 | Dec 31 | Dec 21 | Dec 12 | Dec 6 | Nov 30 |
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 20 | Oct 6 | Oct 31 |
| Freeze (32°F) | Oct 3 | Oct 23 | Nov 18 |
| Hard (28°F) | Oct 20 | Nov 12 | Dec 10 |
| Severe (24°F) | Nov 4 | Dec 1 | Jan 11 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 20 | Sep 27 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 14 | Oct 20 | Oct 31 |
| 32°F | Oct 3 | Oct 9 | Oct 14 | Oct 18 | Oct 23 | Oct 28 | Nov 2 | Nov 8 | Nov 18 |
| 28°F | Oct 20 | Oct 27 | Nov 1 | Nov 7 | Nov 12 | Nov 18 | Nov 25 | Dec 1 | Dec 10 |
| 24°F | Nov 4 | Nov 13 | Nov 20 | Nov 27 | Dec 1 | Dec 9 | Dec 18 | Dec 28 | Jan 11 |
| 20°F | Nov 14 | Nov 27 | Dec 1 | Dec 7 | Dec 14 | Dec 25 | Jan 1 | Jan 14 | Feb 9 |
| 16°F | Nov 28 | Dec 2 | Dec 7 | Dec 11 | Dec 20 | Dec 29 | Jan 4 | Jan 15 | Feb 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: Portland-Hillsboro Ap, Or, about 6.8 miles away@if(!empty($station['elevation_ft'])), at 204 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 Hillsboro, OR?
On average, the last spring frost (32°F) around Hillsboro, OR is about Apr 16. In cooler years it can run later, so for a safer bet many gardeners wait until Mar 25.
When is the first frost in the fall?
The first fall frost around Hillsboro, OR typically arrives about Oct 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 Apr 16 on average, or Mar 25 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 191 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 97123 Planting calendar → Oregon frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026