Harman US

Frost Dates for Rio Vista, CA

Last spring frost
Jan 12
First fall frost
Dec 19
Growing season
343 days
Hardiness zone
9b

In an average year around Rio Vista, CA, the last spring frost (32°F) is about Jan 12 and the first fall frost is about Dec 19, giving roughly a 343-day growing season. To be safe most years, wait until Dec 20 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.

Last spring frost - Rio Vista, CA
Frost intensity Early (10%) Average (50%) Late (90%)
Light (36°F) Mar 12 Feb 8 Jan 11
Freeze (32°F) Feb 1 Jan 12 Dec 20
Hard (28°F) Jan 22 Jan 2 Dec 16
Show full probability table (all thresholds & percentiles)
°F 10% 20% 30% 40% 50% 60% 70% 80% 90%
36°F Mar 12 Mar 3 Feb 23 Feb 14 Feb 8 Feb 3 Jan 29 Jan 21 Jan 11
32°F Feb 1 Jan 28 Jan 22 Jan 16 Jan 12 Jan 7 Jan 2 Dec 29 Dec 20
28°F Jan 22 Jan 15 Jan 10 Jan 5 Jan 2 Dec 30 Dec 28 Dec 23 Dec 16

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.

First fall frost - Rio Vista, CA
Frost intensity Early (10%) Average (50%) Late (90%)
Light (36°F) Nov 18 Dec 4 Dec 28
Freeze (32°F) Nov 29 Dec 19 Jan 12
Hard (28°F) Dec 9 Dec 29 Jan 16
Show full probability table (all thresholds & percentiles)
°F 10% 20% 30% 40% 50% 60% 70% 80% 90%
36°F Nov 18 Nov 24 Nov 29 Dec 1 Dec 4 Dec 8 Dec 12 Dec 17 Dec 28
32°F Nov 29 Dec 5 Dec 10 Dec 15 Dec 19 Dec 23 Dec 29 Jan 3 Jan 12
28°F Dec 9 Dec 18 Dec 22 Dec 27 Dec 29 Jan 1 Jan 4 Jan 10 Jan 16

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

These dates are computed from the nearest official weather station with long-term records: Antioch Pumping Plt #3, Ca, about 11.7 miles away@if(!empty($station['elevation_ft'])), at 60 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.

@endif
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 Rio Vista, CA?

On average, the last spring frost (32°F) around Rio Vista, CA is about Jan 12. In cooler years it can run later, so for a safer bet many gardeners wait until Dec 20.

When is the first frost in the fall?

The first fall frost around Rio Vista, CA typically arrives about Dec 19. 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 Jan 12 on average, or Dec 20 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 343 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 94571 Planting calendar → California frost dates →

Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026