USDA Hardiness Zone 9a
Frost Dates for 95401 — Santa Rosa, California
NOAA 1991–2020 normals from Santa Rosa, CA (166 ft), 2 miles northeast.
Updated
In Santa Rosa, the last spring frost (32°F) is around February 25 in half of years and has passed by March 29 in nine years out of ten. The first fall frost comes around December 1, as early as November 10 one year in ten, leaving a typical freeze-free season of 279 days (NOAA, Santa Rosa, CA).
- Last spring frost
- February 25
- First fall frost
- December 1
- Growing season
- 279 days
- Hardiness zone
- 9a
50% probability
50% probability
freeze-free, 50%
20 to 25°F (-6.7 to -3.9°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 20 observed
NOAA normal
Frost risk by date in Santa Rosa
Half of springs at Santa Rosa, CA see their last 32°F night by February 25; only one in ten is past it by January 21, and one in ten still has one after March 29. Planting tender crops after March 7 leaves a 30% risk of a frost on them, after March 16 20%, and after March 29 10%. The 32 days between the even-odds date and the one-in-ten date is wider than at 55% of the 220 California stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by December 1 in half of years, as early as November 10 one year in ten, and holds off past December 24 one year in ten. A hard freeze of 28°F follows 15 days later, around December 16; in spring the one-in-ten date for 28°F is February 24, 33 days before the 32°F one. The freeze-free season lasts 279 days in a typical year, longer than at 50% of the 219 California stations; it reaches 319 days one year in ten and falls short of 244 one year in ten. On average 15 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 37 days longer, to about April 3, and return around November 14. A 24°F night is unusual: 30% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Mar 6 | Mar 15 | Mar 23 | Mar 30 | Apr 3 | Apr 8 | Apr 12 | Apr 18 | Apr 25 |
| 32°F99% of yrs | Jan 21 | Feb 1 | Feb 11 | Feb 18 | Feb 25 | Mar 1 | Mar 7 | Mar 16 | Mar 29 |
| 28°F83% of yrs | Dec 22 | Dec 30 | Jan 6 | Jan 13 | Jan 20 | Jan 27 | Feb 2 | Feb 11 | Feb 24 |
| 24°F30% of yrs | too rare for a date | ||||||||
| 20°F2% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 31 | Nov 3 | Nov 6 | Nov 10 | Nov 14 | Nov 17 | Nov 21 | Nov 25 | Dec 1 |
| 32°F99% of yrs | Nov 10 | Nov 17 | Nov 21 | Nov 27 | Dec 1 | Dec 3 | Dec 6 | Dec 12 | Dec 24 |
| 28°F83% of yrs | Nov 26 | Dec 1 | Dec 5 | Dec 11 | Dec 16 | Dec 22 | Jan 1 | Jan 5 | Jan 19 |
| 24°F30% of yrs | too rare for a date | ||||||||
| 20°F2% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Santa Rosa, CA, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 95401 →Compare Santa Rosa with another place →
Weather by month in Santa Rosa
August is the warmest month at Santa Rosa, CA, averaging 83°F by day and 53°F at night; December is the coldest at 59°F and 38°F. From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 68% of years and March still brings one in 36% of years.
Warmth for growing adds up to 3,509 growing degree days a year (base 50°F), fewer than at 72% of the 283 California stations. 37% of them (1,309) have built up by the end of June, and August adds the most, 550. Precipitation totals 31.7 inches a year, most in December (6.5") and least in July (0.0"); May to September bring 6% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 60 | 38 | 5.8 | 81% | 4 | 41 |
| Feb | 64 | 40 | 6.4 | 68% | 3 | 83 |
| Mar | 67 | 42 | 4.3 | 36% | 1 | 151 |
| Apr | 71 | 44 | 2.0 | 8% | 0 | 220 |
| May | 75 | 48 | 1.3 | 0% | 0 | 346 |
| Jun | 80 | 51 | 0.3 | 0% | 0 | 469 |
| Jul | 82 | 52 | 0.0 | 0% | 0 | 522 |
| Aug | 83 | 53 | 0.0 | 1% | 0 | 550 |
| Sep | 84 | 51 | 0.2 | 0% | 0 | 524 |
| Oct | 79 | 48 | 1.6 | 0% | 0 | 411 |
| Nov | 67 | 42 | 3.3 | 46% | 2 | 155 |
| Dec | 59 | 38 | 6.5 | 85% | 6 | 37 |
Monthly normals 1991–2020 at Santa Rosa, CA (166 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Santa Rosa Sonoma Co Airport, CA, 6 miles northwest of Santa Rosa, has a last frost 5 days later (March 2), a first frost 11 days earlier (November 20), a season 17 days shorter.
When it snows in Santa Rosa, California
Measurable snow is rare here: only 0 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Santa Rosa, CA, 2.1 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 95401
| When | What to do |
|---|---|
| December 17 – December 31 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 31 – January 14 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 28 – February 11 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 25 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 8 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 17 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 1 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 95401 is 2 miles from Santa Rosa, CA, which stands at 166 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station; its figures are presented in full for 94928 (Rohnert Park). The 2023 USDA Plant Hardiness Zone Map lists ZIP 95401 in zone 9a, the band where the coldest night of the year averaged 20 to 25°F (-6.7 to -3.9°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across California →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.