When to plant in Hillsborough, CA
USDA Zone 10aEverything below — frost dates, hardiness zone, and what to plant when in Hillsborough, California — is derived from the closest NOAA station with complete climate normals.
With only about -3 frost-free days, Hillsborough has a short season — start heat-lovers indoors early, favor quick-maturing varieties, and use row cover to stretch both ends. In zone 10a, frost is a minor factor for Hillsborough — most perennials thrive, and annual vegetables can go out early and stay late.
The average first fall frost in Hillsborough is now 5 days earlier than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
SAN FRANCISCO INTL AP · 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 Hillsborough’s own odds, recorded at SAN FRANCISCO INTL AP.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Feb 14 | Jan 8 | Dec 16 | Dec 5 | Dec 24 | Jan 24 |
| 32°F | Jan 13 | Dec 29 | Dec 11 | Dec 11 | Dec 26 | Jan 13 |
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 Hillsborough, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 12 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.
Hillsborough planting FAQ
When is the last spring frost in Hillsborough, CA?
Hillsborough's average last spring frost falls near December 29 — the 50% mark at 32°F in the 1991–2020 normals. Hold tender transplants until the risk has passed, then plant out.
When is the first fall frost in Hillsborough, CA?
In Hillsborough, the first 32°F freeze of fall lands around December 26 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is Hillsborough in?
Hillsborough is in USDA hardiness zone 10a. In zone 10a, winters are mild — many tender perennials overwinter here.
How long is the growing season in Hillsborough?
Hillsborough has about -3 frost-free days — a short growing season — between the average last spring frost (December 29) and first fall frost (December 26).
When should I plant tomatoes in Hillsborough?
For Hillsborough, sow tomatoes indoors about November 3–November 17 and move the seedlings out around January 5, after the last spring frost.
Never miss a window in Hillsborough
An email when it’s time to start seeds, transplant, and sow — timed to Hillsborough’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Burlingame · 4 km
- San Mateo · 4 km
- Millbrae · 6 km
- Belmont · 7 km
- Foster City · 10 km
- San Bruno · 10 km
- San Carlos · 10 km
- South San Francisco · 11 km
Frost dates recorded at SAN FRANCISCO INTL AP, 7 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 Hillsborough, CA — Frost Dates & Zone 10a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USW00023234. Retrieved from https://blissgarden.com/california/hillsborough.