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

Planting zone for 94309 — Palo Alto, CA

ZIP code 94309 (Palo Alto, Santa Clara County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F. The median last spring frost is February 1 and the first fall frost December 7.

Where ZIP 94309 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 frostFeb 1
First frostDec 7
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 Palo Alto, 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 in Palo Alto, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostFebruary 1median — 50% chance of a later frost
Safe for tender plantsMarch 4only 10% chance of frost after
First fall frostDecember 7median — 10% chance by Nov 20
Growing season310 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 4 and returns around December 22.

From the NOAA station Palo Alto, CA — within 1 mile, elevation 26 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 94309

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Dec 21 – Jan 4
SpinachSow outdoors · Dec 21 – Jan 11
Broccoli, cabbageStart indoors · Nov 23 – Dec 7
Broccoli, cabbageTransplant · Jan 11 – Jan 25
Onion setsPlant outdoors · Jan 4 – Jan 18
PotatoesPlant outdoors · Jan 11 – Jan 25
LettuceSow outdoors · Jan 4 – Jan 18
Carrots, beetsSow outdoors · Jan 11 – Jan 25
TomatoesStart indoors · Dec 7 – Dec 21
TomatoesTransplant · Feb 8 – Feb 22
Peppers, eggplantStart indoors · Nov 23 – Dec 7
Peppers, eggplantTransplant · Feb 15 – Mar 1
BeansSow outdoors · Feb 8 – Feb 22
Sweet cornSow outdoors · Feb 8 – Feb 22
Cucumbers, squashSow outdoors · Feb 8 – Feb 22
Fall lettuce, spinachSow outdoors · Oct 12 – Oct 26
GarlicPlant cloves · Nov 23 – Dec 28
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Feb 1) and first fall frost (Dec 7) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 94309 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 Palo Alto, CA

The soil mapped at the center of ZIP 94309 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 94309; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Palo Alto, CA

Summer high80 °Faverage high, September
Winter low39 °Faverage low, January
Hot days12days a year at 90 °F or more
Freezing nights14nights a year at 32 °F or less
Growing degree days3,364base 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
Precipitation15.1 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°32 °FJanuary: average high 58 °F, low 39 °F 58°39° JanFebruary: average high 61 °F, low 41 °F 61°41° FebMarch: average high 66 °F, low 44 °F 66°44° MarApril: average high 70 °F, low 45 °F 70°45° AprMay: average high 73 °F, low 50 °F 73°50° MayJune: average high 79 °F, low 53 °F 79°53° JunJuly: average high 79 °F, low 56 °F 79°56° JulAugust: average high 79 °F, low 55 °F 79°55° AugSeptember: average high 80 °F, low 53 °F 80°53° SepOctober: average high 74 °F, low 48 °F 74°48° OctNovember: average high 64 °F, low 43 °F 64°43° NovDecember: average high 58 °F, low 39 °F 58°39° Dec

Precipitation by month inches

0″1″2″3″4″January: 2.95 in precipitation 3.0 JanFebruary: 3.18 in precipitation 3.2 FebMarch: 2.19 in precipitation 2.2 MarApril: 0.97 in precipitation 1.0 AprMay: 0.44 in precipitation 0.4 MayJune: 0.10 in precipitation 0.1 JunJuly: 0.00 in precipitation 0.0 JulAugust: 0.03 in precipitation 0.0 AugSeptember: 0.07 in precipitation 0.1 SepOctober: 0.64 in precipitation 0.6 OctNovember: 1.60 in precipitation 1.6 NovDecember: 2.95 in precipitation 3.0 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Palo Alto, CA (within 1 mile); precipitation: Palo Alto, CA (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

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

943029b
Palo Alto, CA · <1 mi
943019b
Palo Alto, CA · <1 mi
9430310a
Palo Alto, CA · 2 mi
943069b
Palo Alto, CA · 2 mi
943059b
Stanford, CA · 2 mi
940259b
Menlo Park, CA · 2 mi
943049b
Palo Alto, CA · 3 mi
940279b
Atherton, CA · 3 mi

All 6 ZIP codes in Palo Alto → · California planting zones →

Questions about 94309

What planting zone is ZIP code 94309?

ZIP code 94309 (Palo Alto, 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).

When is the last frost in Palo Alto, CA?

The median last spring frost (32 °F) near 94309 is February 1; after March 4 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Palo Alto station.

When is the first frost in Palo Alto, CA?

The median first fall frost near 94309 is December 7, giving a median frost-free growing season of 310 days.

When should I plant tomatoes in 94309?

Start tomato seeds indoors around Dec 7 – Dec 21 and set transplants outside around Feb 8 – Feb 22, one to three weeks after the median last frost.

How much rain and snow does 94309 get?

About 15.1 inches of precipitation a year (NOAA 1991–2020 normals, Palo Alto station).

How hot do summers get in Palo Alto, CA?

The average high peaks at 80 °F in September, with about 12 days a year at 90 °F or more.

What kind of soil does 94309 have?

The USDA soil survey maps Flaskan at the center of ZIP 94309: sandy loam, well drained, pH about 6.4 (slightly acidic).

Did spring come early in Palo Alto, CA in 2026?

Spring leaf-out near 94309 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 Palo Alto, CA?

Intermediate onions: the longest day near 94309 is 14 h 45 min, so day-neutral types bulb best; long-day varieties may not bulb fully.