Last spring frost
May 15
Frost Dates for Grass Valley, OR
First fall frost
Oct 11
Growing season
147 days
Hardiness zone
7a
In an average year around Grass Valley, OR, the last spring frost (32°F) is about May 15 and the first fall frost is about Oct 11, giving roughly a 147-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 27 | Jun 7 | May 15 |
| Freeze (32°F) | Jun 6 | May 15 | Apr 29 |
| Hard (28°F) | May 21 | Apr 30 | Apr 12 |
| Severe (24°F) | May 7 | Apr 9 | Mar 8 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 27 | Jun 21 | Jun 16 | Jun 11 | Jun 7 | Jun 3 | May 30 | May 25 | May 15 |
| 32°F | Jun 6 | May 30 | May 26 | May 21 | May 15 | May 11 | May 7 | May 3 | Apr 29 |
| 28°F | May 21 | May 12 | May 7 | May 3 | Apr 30 | Apr 27 | Apr 23 | Apr 18 | Apr 12 |
| 24°F | May 7 | Apr 30 | Apr 23 | Apr 18 | Apr 9 | Apr 2 | Mar 29 | Mar 19 | Mar 8 |
| 20°F | Apr 18 | Mar 31 | Mar 22 | Mar 13 | Mar 7 | Mar 2 | Feb 25 | Feb 17 | Feb 3 |
| 16°F | Mar 11 | Mar 2 | Feb 26 | Feb 21 | Feb 15 | Feb 7 | Jan 29 | Jan 15 | Jan 5 |
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 7 | Sep 29 | Oct 12 |
| Freeze (32°F) | Sep 27 | Oct 11 | Oct 26 |
| Hard (28°F) | Oct 6 | Oct 23 | Nov 9 |
| Severe (24°F) | Oct 18 | Nov 5 | Nov 26 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 7 | Sep 16 | Sep 22 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 12 |
| 32°F | Sep 27 | Oct 1 | Oct 4 | Oct 7 | Oct 11 | Oct 14 | Oct 17 | Oct 20 | Oct 26 |
| 28°F | Oct 6 | Oct 12 | Oct 16 | Oct 19 | Oct 23 | Oct 26 | Oct 29 | Nov 4 | Nov 9 |
| 24°F | Oct 18 | Oct 25 | Oct 29 | Nov 1 | Nov 5 | Nov 9 | Nov 14 | Nov 19 | Nov 26 |
| 20°F | Oct 27 | Nov 4 | Nov 9 | Nov 14 | Nov 18 | Nov 24 | Nov 27 | Dec 2 | Dec 9 |
| 16°F | Nov 4 | Nov 12 | Nov 20 | Nov 26 | Dec 1 | Dec 5 | Dec 12 | Dec 19 | Dec 27 |
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: Kent, Or, about 5.6 miles away@if(!empty($station['elevation_ft'])), at 2,710 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 Grass Valley, OR?
On average, the last spring frost (32°F) around Grass Valley, OR is about May 15. 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 Grass Valley, OR typically arrives about Oct 11. 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 15 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 147 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 97033 Planting calendar → Oregon frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026