Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 94931 — Cotati, CA

ZIP code 94931 (Cotati, Sonoma County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F. The median last spring frost is February 28 and the first fall frost November 25.

Where ZIP 94931 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone9a20 to 25 °F
Coldest night−6.7 to −3.9 °C
Last frostFeb 28
First frostNov 25
2012 zone9b

Was 9b on the 2012 map — half a zone colder now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 9a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Cotati, CA…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Cotati, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostFebruary 28median — 50% chance of a later frost
Safe for tender plantsApril 6only 10% chance of frost after
First fall frostNovember 25median — 10% chance by Nov 9
Growing season271 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 17 and returns around December 9.

From the NOAA station Petaluma Airport, CA — 7 miles away, elevation 20 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 94931

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Jan 17 – Jan 31
SpinachSow outdoors · Jan 17 – Feb 7
Broccoli, cabbageStart indoors · Dec 20 – Jan 3
Broccoli, cabbageTransplant · Feb 7 – Feb 21
Onion setsPlant outdoors · Jan 31 – Feb 14
PotatoesPlant outdoors · Feb 7 – Feb 21
LettuceSow outdoors · Jan 31 – Feb 14
Carrots, beetsSow outdoors · Feb 7 – Feb 21
TomatoesStart indoors · Jan 3 – Jan 17
TomatoesTransplant · Mar 7 – Mar 21
Peppers, eggplantStart indoors · Dec 20 – Jan 3
Peppers, eggplantTransplant · Mar 14 – Mar 28
BeansSow outdoors · Mar 7 – Mar 21
Sweet cornSow outdoors · Mar 7 – Mar 21
Cucumbers, squashSow outdoors · Mar 7 – Mar 21
Fall lettuce, spinachSow outdoors · Sep 30 – Oct 14
GarlicPlant cloves · Nov 11 – Dec 16
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Feb 28) and first fall frost (Nov 25) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 94931 came on Jan 30 — about the same time as the 1991–2020 average (Jan 31).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Soil in Cotati, CA

The soil mapped at the center of ZIP 94931 is Cotati — fine sandy loam, moderately well drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding
pH5.3strongly acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter0.75%low — add compost
Hydrologic groupDwater soaks in very slowly
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Cotati fine sandy loam, 2 to 9 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 94931; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Cotati, CA

Summer high82 °Faverage high, September
Winter low38 °Faverage low, December
Hot days21days a year at 90 °F or more
Freezing nights21nights a year at 32 °F or less
Growing degree days3,210base 50 °F — the season’s usable heat
Longest day14 h 50 mindaylight on June 21
Shortest day9 h 29 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation33.4 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°32 °FJanuary: average high 58 °F, low 39 °F 58°39° JanFebruary: average high 61 °F, low 40 °F 61°40° FebMarch: average high 65 °F, low 42 °F 65°42° MarApril: average high 68 °F, low 44 °F 68°44° AprMay: average high 72 °F, low 47 °F 72°47° MayJune: average high 78 °F, low 50 °F 78°50° JunJuly: average high 81 °F, low 52 °F 81°52° JulAugust: average high 81 °F, low 53 °F 81°53° AugSeptember: average high 82 °F, low 51 °F 82°51° SepOctober: average high 76 °F, low 48 °F 76°48° OctNovember: average high 66 °F, low 42 °F 66°42° NovDecember: average high 58 °F, low 38 °F 58°38° Dec

Precipitation by month inches

0″2″4″6″January: 6.21 in precipitation 6.2 JanFebruary: 6.60 in precipitation 6.6 FebMarch: 4.62 in precipitation 4.6 MarApril: 2.33 in precipitation 2.3 AprMay: 1.32 in precipitation 1.3 MayJune: 0.39 in precipitation 0.4 JunJuly: 0.03 in precipitation 0.0 JulAugust: 0.07 in precipitation 0.1 AugSeptember: 0.12 in precipitation 0.1 SepOctober: 1.73 in precipitation 1.7 OctNovember: 3.32 in precipitation 3.3 NovDecember: 6.66 in precipitation 6.7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Petaluma Airport, CA (7 mi away); precipitation: Rohnert Park 0.9 Sw, CA (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

2 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

949269a
Rohnert Park, CA · 1 mi
949279a
Rohnert Park, CA · 1 mi
949289a
Rohnert Park, CA · 2 mi
949519b
Penngrove, CA · 4 mi
954079a
Santa Rosa, CA · 5 mi
949999a
Petaluma, CA · 5 mi
949529b
Petaluma, CA · 7 mi
949539a
Petaluma, CA · 8 mi

California planting zones →

Questions about 94931

What planting zone is ZIP code 94931?

ZIP code 94931 (Cotati, CA) is in USDA hardiness zone 9a on the 2023 map: the coldest night of an average winter reaches 20 to 25 °F (−6.7 to −3.9 °C).

When is the last frost in Cotati, CA?

The median last spring frost (32 °F) near 94931 is February 28; after April 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Petaluma Airport station.

When is the first frost in Cotati, CA?

The median first fall frost near 94931 is November 25, giving a median frost-free growing season of 271 days.

When should I plant tomatoes in 94931?

Start tomato seeds indoors around Jan 3 – Jan 17 and set transplants outside around Mar 7 – Mar 21, one to three weeks after the median last frost.

How much rain and snow does 94931 get?

About 33.4 inches of precipitation a year (NOAA 1991–2020 normals, Rohnert Park 0.9 Sw station).

How hot do summers get in Cotati, CA?

The average high peaks at 82 °F in September, with about 21 days a year at 90 °F or more.

What kind of soil does 94931 have?

The USDA soil survey maps Cotati at the center of ZIP 94931: fine sandy loam, moderately well drained, pH about 5.3 (strongly acidic).

Did spring come early in Cotati, CA in 2026?

Spring leaf-out near 94931 came on Jan 30 in 2026, about the same as the 1991–2020 average (Jan 31), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Cotati, CA?

Intermediate onions: the longest day near 94931 is 14 h 50 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 94931 change?

Yes. The 2012 USDA map put 94931 in zone 9b; the 2023 map puts it in zone 9a. The newer map uses 1991–2020 data and more weather stations.