Foster City, CA planting zone & frost dates
Foster City is in USDA hardiness zone 10a. The last spring frost usually comes around January 17 and the first fall frost around December 12, for a growing season of about 333 days.
Planting calendar for Foster City
Dates are counted from the average last spring frost (January 17) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Nov 22 – Dec 6 Transplant outdoors: Jan 24 – Jan 31 |
| Peppers | Start seeds indoors: Nov 8 – Nov 22 Transplant outdoors: Jan 31 – Feb 7 |
| Eggplant | Start seeds indoors: Nov 8 – Nov 22 Transplant outdoors: Jan 31 – Feb 7 |
| Broccoli | Start seeds indoors: Nov 8 – Nov 22 Transplant outdoors: Dec 20 – Jan 3 |
| Cabbage | Start seeds indoors: Nov 8 – Nov 22 Transplant outdoors: Dec 20 – Jan 3 |
| Onions (sets) | Plant outdoors: Dec 20 – Jan 3 |
| Peas | Sow outdoors: Dec 6 – Dec 20 |
| Spinach | Sow outdoors: Dec 6 – Dec 20 |
| Lettuce | Sow outdoors: Dec 20 – Jan 3 |
| Carrots | Sow outdoors: Dec 20 – Jan 3 |
| Potatoes | Plant outdoors: Dec 20 – Jan 3 |
| Beans | Sow outdoors: Jan 24 – Jan 31 |
| Sweet corn | Sow outdoors: Jan 24 – Jan 31 |
| Cucumbers | Sow outdoors: Jan 24 – Jan 31 |
| Squash & zucchini | Sow outdoors: Jan 24 – Jan 31 |
| Basil | Start seeds indoors: Dec 6 – Dec 20 Transplant outdoors: Jan 24 – Jan 31 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Oct 17 (8 weeks before the average first fall frost on Dec 12).
Useful for zone 10a gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Shade cloth — for hot summers
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Dec 20 | Jan 17 | Feb 16 |
| First 32°F frost in fall is before | Jan 14 | Dec 12 | Nov 24 |
How to read it: in spring there is a 10% chance of a frost after February 16, so that is a safe date for tender plants. In fall there is a 10% chance of frost before November 24. A hard freeze (28°F) usually ends around December 31.
Nearby cities
- Belmont zone 10a, last frost Jan 17
- San Carlos zone 10a, last frost Jan 17
- San Mateo zone 10a
- Redwood City zone 10a, last frost Jan 17
- Burlingame zone 10a
- Hillsborough zone 10a
- Millbrae zone 10a
- Menlo Park zone 9b, last frost Feb 1
Questions
What growing zone is Foster City, CA?
Foster City is in USDA Plant Hardiness Zone 10a (average extreme winter low 30°F to 35°F), according to the USDA 2023 map.
When is the last frost in Foster City?
The average last spring frost (32°F) in Foster City is January 17. There is still a 10% chance of frost until February 16.
When can I plant tomatoes in Foster City?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around Jan 24 – Jan 31. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Redwood City, CA (USC00047339), 9.5 km (5.9 mi) from the city center, elevation 9 m, based on 29 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.