When to plant in Alamo, CA
USDA Zone 9bEverything below — frost dates, hardiness zone, and what to plant when in Alamo, California — is derived from the closest NOAA station with complete climate normals.
A generous ~289-day season lets Alamo gardeners direct-sow more and still ripen long-maturity crops like melons and winter squash. Zone 9b is warm enough that Alamo can grow subtropical perennials, and the short (or absent) frost period barely limits the annual calendar.
Frost probability
MT DIABLO JUNCTION · 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 Alamo’s own odds, recorded at MT DIABLO JUNCTION.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 20 | Apr 19 | Mar 16 | Nov 6 | Nov 29 | Dec 20 |
| 32°F | Apr 15 | Mar 8 | Jan 12 | Nov 23 | Dec 22 | Feb 11 |
| 28°F | Mar 23 | Feb 8 | Dec 21 | Dec 8 | Jan 16 | Mar 3 |
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 Alamo, 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.
Alamo planting FAQ
When is the last spring frost in Alamo, CA?
On average, the last spring frost in Alamo is around March 8 (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 Alamo, CA?
Expect Alamo's first fall frost near December 22 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is Alamo in?
Alamo is in USDA hardiness zone 9b. In zone 9b, winters are mild — many tender perennials overwinter here.
How long is the growing season in Alamo?
There are roughly 289 frost-free days in Alamo (a long growing season), running from the average last frost around March 8 to the first fall frost near December 22.
When should I plant tomatoes in Alamo?
In Alamo, start tomato seeds indoors around January 11–January 25, then transplant seedlings outdoors around March 15 once the danger of frost has passed.
Never miss a window in Alamo
An email when it’s time to start seeds, transplant, and sow — timed to Alamo’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Walnut Creek · 6 km
- Danville · 6 km
- Moraga · 10 km
- Lafayette · 10 km
- Blackhawk · 10 km
- Clayton · 12 km
- San Ramon · 12 km
- Pleasant Hill · 12 km
Frost dates recorded at MT DIABLO JUNCTION, 8 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 Alamo, CA — Frost Dates & Zone 9b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00045915. Retrieved from https://blissgarden.com/california/alamo.