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

Planting zone for 94023 — Los Altos, CA

ZIP code 94023 (Los Altos, Santa Clara County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F.

Where ZIP 94023 is

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 Los Altos, 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 Moffett Federal Airfield, CA — 4 miles away, elevation 39 ft) the median growing season is 353 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 94023 came on Jan 27 — about the same time as the 1991–2020 average (Jan 28).

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 Los Altos, CA

The soil mapped at the center of ZIP 94023 is Flaskan — sandy loam, well drained. Much of the area is built over (urban land); this is the natural soil underneath.

TextureSandy loamdrains and warms fast; dries out and needs more feeding
pH6.4slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2%moderate
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Urban land-Flaskan complex, 0 to 2 percent slopes.

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 94023; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Los Altos, CA

Summer high78 °Faverage high, September
Winter low42 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights2nights a year at 32 °F or less
Growing degree days3,761base 50 °F — the season’s usable heat
Longest day14 h 45 mindaylight on June 21
Shortest day9 h 35 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation17 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 42 °F 59°42° JanFebruary: average high 62 °F, low 45 °F 62°45° FebMarch: average high 65 °F, low 47 °F 65°47° MarApril: average high 68 °F, low 49 °F 68°49° AprMay: average high 72 °F, low 53 °F 72°53° MayJune: average high 76 °F, low 56 °F 76°56° JunJuly: average high 77 °F, low 59 °F 77°59° JulAugust: average high 77 °F, low 59 °F 77°59° AugSeptember: average high 78 °F, low 57 °F 78°57° SepOctober: average high 74 °F, low 53 °F 74°53° OctNovember: average high 66 °F, low 46 °F 66°46° NovDecember: average high 59 °F, low 42 °F 59°42° Dec

Precipitation by month inches

0″1″2″3″4″January: 3.47 in precipitation 3.5 JanFebruary: 3.57 in precipitation 3.6 FebMarch: 2.26 in precipitation 2.3 MarApril: 1.13 in precipitation 1.1 AprMay: 0.49 in precipitation 0.5 MayJune: 0.14 in precipitation 0.1 JunJuly: 0.00 in precipitation 0.0 JulAugust: 0.04 in precipitation 0.0 AugSeptember: 0.09 in precipitation 0.1 SepOctober: 0.75 in precipitation 0.8 OctNovember: 1.55 in precipitation 1.6 NovDecember: 3.53 in precipitation 3.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Moffett Federal Airfield, CA (4 mi away); precipitation: Mountain View 1.2 S, CA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

940409b
Mountain View, CA · 2 mi
9403910a
Mountain View, CA · 2 mi
9404210a
Mountain View, CA · 2 mi
940419b
Mountain View, CA · 2 mi
943069b
Palo Alto, CA · 2 mi
940249b
Los Altos, CA · 3 mi
940229b
Los Altos, CA · 3 mi
943049b
Palo Alto, CA · 3 mi

All 3 ZIP codes in Los Altos → · California planting zones →

Questions about 94023

What planting zone is ZIP code 94023?

ZIP code 94023 (Los Altos, 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 94023 get?

About 17 inches of precipitation a year (NOAA 1991–2020 normals, Mountain View 1.2 S station).

How hot do summers get in Los Altos, CA?

The average high peaks at 78 °F in September, with about 9 days a year at 90 °F or more.

What kind of soil does 94023 have?

The USDA soil survey maps Flaskan at the center of ZIP 94023: sandy loam, well drained, pH about 6.4 (slightly acidic).

Did spring come early in Los Altos, CA in 2026?

Spring leaf-out near 94023 came on Jan 27 in 2026, about the same as the 1991–2020 average (Jan 28), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Los Altos, CA?

Intermediate onions: the longest day near 94023 is 14 h 45 min, so day-neutral types bulb best; long-day varieties may not bulb fully.