Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 94552 — Castro Valley, CA

ZIP code 94552 (Castro Valley, Alameda County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F.

Where ZIP 94552 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone9b25 to 30 °F
Coldest night−3.9 to −1.1 °C
Last frostrare
First frostrare
2012 zone9b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 9b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Castro Valley, CA…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates

A 32 °F frost doesn't happen here in most winters. At the nearest station (NOAA station Hayward Air Terminal, CA — 7 miles away, elevation 43 ft) the median growing season is 365 days. When frost does come, it is a midwinter night or two; cover tender plants when a freeze is forecast.

Frost data: NOAA NCEI U.S. Climate Normals 1991–2020.

When spring arrived in 2026

In 2026, spring leaf-out near 94552 came on Jan 27 — 3 days earlier than the 1991–2020 average (Jan 30).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Soil in Castro Valley, CA

The soil mapped at the center of ZIP 94552 is Los Gatos — loam, well drained.

TextureLoama good balance for most vegetables
pH7.0neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3%moderate
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Los Gatos-Los Osos complex, 30 to 75 percent slopes, eroded, MLRA 15.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 94552; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Castro Valley, CA

Summer high77 °Faverage high, September
Winter low43 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights1nights a year at 32 °F or less
Growing degree days3,627base 50 °F — the season’s usable heat
Longest day14 h 46 mindaylight on June 21
Shortest day9 h 33 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation21.8 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°32 °FJanuary: average high 59 °F, low 43 °F 59°43° JanFebruary: average high 62 °F, low 45 °F 62°45° FebMarch: average high 64 °F, low 47 °F 64°47° MarApril: average high 67 °F, low 50 °F 67°50° AprMay: average high 69 °F, low 52 °F 69°52° MayJune: average high 74 °F, low 55 °F 74°55° JunJuly: average high 75 °F, low 57 °F 75°57° JulAugust: average high 76 °F, low 58 °F 76°58° AugSeptember: average high 77 °F, low 58 °F 77°58° SepOctober: average high 74 °F, low 54 °F 74°54° OctNovember: average high 65 °F, low 47 °F 65°47° NovDecember: average high 59 °F, low 43 °F 59°43° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.97 in precipitation 4.0 JanFebruary: 3.94 in precipitation 3.9 FebMarch: 3.19 in precipitation 3.2 MarApril: 1.76 in precipitation 1.8 AprMay: 0.75 in precipitation 0.8 MayJune: 0.24 in precipitation 0.2 JunJuly: 0.01 in precipitation 0.0 JulAugust: 0.06 in precipitation 0.1 AugSeptember: 0.17 in precipitation 0.2 SepOctober: 1.04 in precipitation 1.0 OctNovember: 2.17 in precipitation 2.2 NovDecember: 4.46 in precipitation 4.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Hayward Air Terminal, CA (7 mi away); precipitation: Castro Valley 0.4 Nne, CA (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

4 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

945429b
Hayward, CA · 4 mi
945839b
San Ramon, CA · 5 mi
9454310a
Hayward, CA · 5 mi
9454110a
Hayward, CA · 5 mi
945379b
Fremont, CA · 5 mi
9454010a
Hayward, CA · 5 mi
9455710a
Hayward, CA · 5 mi
945449b
Hayward, CA · 6 mi

All 2 ZIP codes in Castro Valley → · California planting zones →

Questions about 94552

What planting zone is ZIP code 94552?

ZIP code 94552 (Castro Valley, CA) is in USDA hardiness zone 9b on the 2023 map: the coldest night of an average winter reaches 25 to 30 °F (−3.9 to −1.1 °C).

How much rain and snow does 94552 get?

About 21.8 inches of precipitation a year (NOAA 1991–2020 normals, Castro Valley 0.4 Nne station).

How hot do summers get in Castro Valley, CA?

The average high peaks at 77 °F in September, with about 9 days a year at 90 °F or more.

What kind of soil does 94552 have?

The USDA soil survey maps Los Gatos at the center of ZIP 94552: loam, well drained, pH about 7.0 (neutral).

Did spring come early in Castro Valley, CA in 2026?

Spring leaf-out near 94552 came on Jan 27 in 2026, 3 days earlier than the 1991–2020 average (Jan 30), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Castro Valley, CA?

Intermediate onions: the longest day near 94552 is 14 h 46 min, so day-neutral types bulb best; long-day varieties may not bulb fully.