When to plant in Castro Valley, CA
USDA Zone 10aHere are the average frost dates, USDA hardiness zone, and a month-by-month planting calendar for Castro Valley, California — all computed from Castro Valley's nearest NOAA weather station.
Castro Valley enjoys a long ~357-day frost-free season — you can succession-sow, fit in a second crop, and grow long-season heat-lovers with room to spare. Zone 10a is warm enough that Castro Valley can grow subtropical perennials, and the short (or absent) frost period barely limits the annual calendar.
The average first fall frost in Castro Valley is now 5 days earlier than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
HAYWARD AIR TERMINAL · 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 Castro Valley’s own odds, recorded at HAYWARD AIR TERMINAL.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Feb 28 | Jan 29 | Dec 30 | Nov 24 | Dec 12 | Jan 11 |
| 32°F | Jan 27 | Jan 2 | Dec 13 | Dec 6 | Dec 25 | Jan 20 |
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 Castro Valley, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 19 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.
Castro Valley planting FAQ
When is the last spring frost in Castro Valley, CA?
Castro Valley's average last spring frost falls near January 2 — 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 Castro Valley, CA?
In Castro Valley, 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 Castro Valley in?
Castro Valley is in USDA hardiness zone 10a. In zone 10a, winters are mild — many tender perennials overwinter here.
How long is the growing season in Castro Valley?
There are roughly 357 frost-free days in Castro Valley (a long growing season), running from the average last frost around January 2 to the first fall frost near December 25.
When should I plant tomatoes in Castro Valley?
In Castro Valley, start tomato seeds indoors around November 7–November 21, then transplant seedlings outdoors around January 9 once the danger of frost has passed.
Never miss a window in Castro Valley
An email when it’s time to start seeds, transplant, and sow — timed to Castro Valley’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Fairview · 4 km
- Cherryland · 5 km
- Ashland · 5 km
- San Lorenzo · 7 km
- San Leandro · 9 km
- Hayward · 10 km
- Union City · 12 km
- San Ramon · 13 km
Frost dates recorded at HAYWARD AIR TERMINAL, 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 Castro Valley, CA — Frost Dates & Zone 10a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USW00093228. Retrieved from https://blissgarden.com/california/castro-valley.