What zone 9a means for Petaluma
Hardiness zones are based on the average of the coldest night of each winter over 30 years (1991 to 2020). In zone 9a, that average is 20 to 25°F (-7 to -4°C). Plants labeled hardy to zone 9a or colder should survive a typical Petaluma winter. A plant rated only to a warmer zone will need a sheltered spot, a pot you can bring inside, or treating as an annual.
Not every part of Petaluma is the same: its ZIP codes fall in zones 9a, 9b. Check your own ZIP code in the table below.
How Petaluma compares with the rest of California
California runs from zone 5b to zone 11a on the 2023 map. About 9% of the state's ZIP codes share Petaluma's zone 9a. Gardeners in colder parts of the state may need hardier plants, while those in warmer parts can grow some plants that would struggle here.
Frost dates in Petaluma
These are the median dates of the last and first 32°F freeze from NOAA's 1991 to 2020 climate normals, using the weather station closest to Petaluma (Petaluma Airport, about 1 km away). Half of years have a later last frost, so tender plants are safest a week or two after the date. Your own garden can differ with elevation and shelter: check your exact ZIP code above.
Vegetable planting calendar for Petaluma
Purdue Extension groups vegetables by how much frost they can take and times planting from the average last spring frost. Applied to Petaluma's last frost of February 28:
| Group | Plant outdoors | Crops |
|---|---|---|
| Hardy crops (tolerate a hard frost) 4 to 6 weeks before the average last spring frost | January 17 to January 31 | Asparagus, broccoli, Brussels sprouts, cabbage, collards, horseradish, kale, kohlrabi, leek, mustard, onion, peas, potato, radish, rhubarb, spinach, turnip |
| Semi-hardy crops (tolerate a light frost) 2 to 4 weeks before the average last spring frost | January 31 to February 14 | Beet, carrot, cauliflower, celery, chard, Chinese cabbage, lettuce, mustard, parsnip |
| Tender crops (damaged by frost) after the average last spring frost, once nights stay above 50°F | From February 28 | Bean, sweet corn, tomato |
| Very tender crops (warm season) at least 2 weeks after the average last spring frost, once nights stay above 60 to 65°F | From March 14 | Cucumber, eggplant, melons, okra, pepper, pumpkin, squash, sweet potato |
Spring planting for direct seeding or transplants. A late cold snap can still happen, so watch the forecast and protect tender plants. Want today's answer for your ZIP code? Use what to plant now.
Sources: NOAA NCEI U.S. Climate Normals 1991 to 2020; Purdue Extension, Indiana Vegetable Planting Calendar (HO-186-W).
Choosing plants for zone 9a
When you shop, look for the hardiness range on the tag or in the catalog, such as "zones 4 to 9". Pick perennials, shrubs and trees whose range includes 9a. If you are set on a plant rated only to a warmer zone, plant it in a sheltered spot against a south-facing wall, mulch the roots before winter, or grow it in a container you can move into a garage. Zones only cover winter cold, so also check sun, water and soil needs. More in how to read a plant tag.
Petaluma ZIP codes and zones
ZIP codes GeoNames assigns to Petaluma, which can include PO box ZIP codes.
Other cities in California
Frequently asked questions
When is the last frost in Petaluma?
The median last spring frost (32°F) near Petaluma is February 28, and the median first fall frost is November 25, based on NOAA 1991 to 2020 climate normals.
What planting zone is Petaluma in?
Petaluma, CA is in USDA plant hardiness zone 9a (ZIP codes range from 9a to 9b). Zone 9a means an average coldest winter night of 20 to 25°F (-7 to -4°C), based on the 2023 USDA map.
Did Petaluma's zone change in 2023?
The 2023 USDA map uses weather data from 1991 to 2020. The USDA says about half of the country shifted to the next warmer half zone compared with the 2012 map, while the rest stayed in the same half zone.
Zones: 2023 USDA Plant Hardiness Zone Map ZIP code listings, PRISM Climate Group, Oregon State University. Place names: GeoNames (CC BY 4.0). Not the official USDA map. Our data.