When to plant in Alum Rock, CA
USDA Zone 9bEverything below — frost dates, hardiness zone, and what to plant when in Alum Rock, California — is derived from the closest NOAA station with complete climate normals.
With about 357 frost-free days, Alum Rock supports back-to-back plantings; stagger sowings every few weeks to keep beds productive spring through fall. In zone 9b, frost is a minor factor for Alum Rock — most perennials thrive, and annual vegetables can go out early and stay late.
The average last spring frost in Alum Rock is now 11 days earlier than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
SAN JOSE · 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 Alum Rock’s own odds, recorded at SAN JOSE.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Feb 27 | Jan 26 | Dec 27 | Nov 22 | Dec 10 | Jan 4 |
| 32°F | Jan 23 | Jan 2 | Dec 14 | Dec 4 | Dec 25 | Jan 14 |
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 Alum Rock, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 16 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.
Alum Rock planting FAQ
When is the last spring frost in Alum Rock, CA?
Plan for the last spring frost in Alum Rock around January 2 (the date it has a 50% chance of a 32°F freeze). Anything frost-sensitive should go out after it.
When is the first fall frost in Alum Rock, CA?
In Alum Rock, the first 32°F freeze of fall lands around December 25 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is Alum Rock in?
Alum Rock is in USDA hardiness zone 9b. In zone 9b, winters are mild — many tender perennials overwinter here.
How long is the growing season in Alum Rock?
Alum Rock has about 357 frost-free days — a long growing season — between the average last spring frost (January 2) and first fall frost (December 25).
When should I plant tomatoes in Alum Rock?
For Alum Rock, sow tomatoes indoors about November 7–November 21 and move the seedlings out around January 9, after the last spring frost.
Never miss a window in Alum Rock
An email when it’s time to start seeds, transplant, and sow — timed to Alum Rock’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reachFrost dates recorded at SAN JOSE, 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 Alum Rock, CA — Frost Dates & Zone 9b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00047821. Retrieved from https://blissgarden.com/california/alum-rock.