When to plant in Foster City, CA
USDA Zone 10aFoster City, California frost dates, USDA zone, and a full-year planting calendar, drawn from the nearest NOAA station and tuned to the local season.
A generous ~329-day season lets Foster City gardeners direct-sow more and still ripen long-maturity crops like melons and winter squash. Zone 10a is warm enough that Foster City can grow subtropical perennials, and the short (or absent) frost period barely limits the annual calendar.
The average last spring frost in Foster City is now 6 days earlier than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
REDWOOD CITY · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Foster City’s own odds, recorded at REDWOOD CITY.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Mar 31 | Feb 25 | Jan 25 | Nov 8 | Nov 25 | Dec 14 |
| 32°F | Feb 16 | Jan 17 | Dec 20 | Nov 24 | Dec 12 | Jan 14 |
| 28°F | Jan 22 | Dec 31 | Dec 14 | Dec 5 | Dec 26 | Jan 15 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Nothing new to sow or transplant outdoors in the next few weeks — a seasonal lull. Check the full-year calendar below for the next window.
Full-year planting calendar
Each bar is the exact window to take a planting action in Foster City, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 15 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Foster City planting FAQ
When is the last spring frost in Foster City, CA?
On average, the last spring frost in Foster City is around January 17 (50% probability at 32°F, from 1991–2020 NOAA normals). Wait until after this date to set out tender plants like tomatoes and peppers.
When is the first fall frost in Foster City, CA?
The first fall frost in Foster City typically arrives around December 12 (50% probability at 32°F). Harvest or protect frost-sensitive crops before then.
What hardiness zone is Foster City in?
Foster City is in USDA hardiness zone 10a. In zone 10a, winters are mild — many tender perennials overwinter here.
How long is the growing season in Foster City?
There are roughly 329 frost-free days in Foster City (a long growing season), running from the average last frost around January 17 to the first fall frost near December 12.
When should I plant tomatoes in Foster City?
In Foster City, start tomato seeds indoors around November 22–December 6, then transplant seedlings outdoors around January 24 once the danger of frost has passed.
Never miss a window in Foster City
An email when it’s time to start seeds, transplant, and sow — timed to Foster City’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- San Mateo · 5 km
- Redwood City · 6 km
- Belmont · 7 km
- San Carlos · 7 km
- Hillsborough · 10 km
- Burlingame · 10 km
- North Fair Oaks · 11 km
- Menlo Park · 13 km
Frost dates recorded at REDWOOD CITY, 10 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Foster City, CA — Frost Dates & Zone 10a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00047339. Retrieved from https://blissgarden.com/california/foster-city.