When is the last frost in Petaluma, CA?

The average last spring frost (50% probability of 32°F) in Petaluma is around February 28, based on NOAA/NCEI 1991–2020 normals at the Petaluma Ap, CA station (2.8 mi away). Half of years it falls outside that date, so wait 1–2 weeks past it before setting out frost-tender plants.

When is the first fall frost in Petaluma?

The average first fall frost in Petaluma, CA is around November 25, giving roughly a 271-day frost-free growing season.

What planting zone is Petaluma, CA?

Petaluma is in USDA plant hardiness zone 9a (average annual extreme minimum temperature 20 to 25°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in Petaluma?

In Petaluma, CA the warmest month is September (avg high 81.6°F) and the coldest is December (avg low 38.4°F). It averages about 25.6″ of precipitation a year.

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Petaluma, CA Planting Calendar & Frost Dates

USDA hardiness zone 9a · ZIP 94999 · elevation 6′ · NOAA & USDA data

Petaluma is in USDA hardiness zone 9a (winters can dip to 20 to 25°F), with a growing season of about 271 days between the average last spring frost (February 28) and first fall frost (November 25). The warmest month is September (avg high 81.6°F); the coldest is December (avg low 38.4°F). It averages 25.6″ of precipitation a year. Start cool-season crops several weeks before the last frost; wait until after it for tomatoes, peppers and other tender crops.

Hardiness zone

min temp 20 to 25°F

Last spring frost

February 28

avg (50% prob, 32°F)

First fall frost

November 25

avg (50% prob, 32°F)

Growing season

271 days

frost-free window

Warmest month

September

avg high 81.6°F

Month-by-month typical weather in Petaluma

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Petaluma Ap, CA (2.8 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)
January	57.6	39	48.3	4.8
February	61.3	40.4	50.8	5.2
March	64.5	41.9	53.2	3.3
April	67.8	43.8	55.8	1.7
May	71.9	47.4	59.6	0.9
June	78.1	50.4	64.3	0.3
July	80.8	52.4	66.6	0
August	81.2	52.8	67	0.1
September	81.6	51.4	66.5	0.1
October	76.4	47.6	62	1.3
November	65.5	42.3	53.9	2.7
December	57.9	38.4	48.1	5.2

What to plant when in Petaluma

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: January 17 · Transplant out: March 7
Peppers	warm	Start seeds indoors: January 3 · Transplant out: March 14
Cucumbers	warm	Direct sow: March 7
Zucchini / squash	warm	Direct sow: March 7
Bush beans	warm	Direct sow: March 7
Sweet corn	warm	Direct sow: March 7
Basil	warm	Transplant out: March 7
Peas	cool	Sow (spring): January 24 · Sow (fall): September 30
Spinach	cool	Sow (spring): January 17 · Sow (fall): September 30
Lettuce	cool	Sow (spring): January 31 · Sow (fall): September 30
Kale	cool	Transplant (spring): February 7 · Sow (fall): September 16
Broccoli	cool	Transplant (spring): February 14
Carrots	cool	Sow (spring): February 7 · Sow (fall): September 16
Onions	cool	Transplant (spring): January 31
Potatoes	cool	Plant seed potatoes: February 14
Radishes	cool	Sow (spring): January 31 · Sow (fall): October 14

Dates are computed from Petaluma's average frost dates using standard cool-/warm-season timing. They're a starting point — a cold spring, a warm microclimate, or a fast-maturing variety can shift them by a week or two.

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Gear that helps you plant on time

Some links below are Amazon affiliate links (tag theboringthin-20). If you buy through them we may earn a small commission at no extra cost to you — it keeps this almanac free. We only list generic, genuinely-useful categories.

Soil thermometer →Know when the ground is warm enough to sow — the honest signal, not the calendar.Seed-starting trays + dome →Start tomatoes & peppers indoors on the schedule below.Seedling heat mat →Warms the soil for faster, more even germination indoors.Floating row cover / frost cloth →Buys you 4–8°F to beat an early or late frost.Raised garden bed kit →Warms and drains faster in spring than in-ground soil.Garden gloves →Basic kit for transplant day.

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Sources & method. Hardiness zone: 2023 USDA Plant Hardiness Zone Map (PRISM Climate Group, Oregon State University). Frost dates & growing season: NOAA/NCEI 1991–2020 U.S. Climate Normals, nearest station with published freeze normals — Petaluma Ap, CA, 2.8 mi (confidence: high). Monthly weather normals: Petaluma Ap, CA, 2.8 mi (confidence: high). ZIP centroid from U.S. Census 2023 ZCTA data. Frost dates are the 50%-probability date — half of years frost occurs outside the stated date. Nothing here is invented; where the nearest station is far, we say so. Last updated 2026-07-22.