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

Planting zone for 94028 — Portola Valley, CA

ZIP code 94028 (Portola Valley, San Mateo County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F. The median last spring frost is February 25 and the first fall frost November 25.

Where ZIP 94028 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 frostFeb 25
First frostNov 25
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 Portola 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 in Portola Valley, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostFebruary 25median — 50% chance of a later frost
Safe for tender plantsApril 11only 10% chance of frost after
First fall frostNovember 25median — 10% chance by Nov 3
Growing season274 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 13 and returns around December 12.

From the NOAA station Woodside Fire Stn 1, CA — 4 miles away, elevation 381 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 94028

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Jan 14 – Jan 28
SpinachSow outdoors · Jan 14 – Feb 4
Broccoli, cabbageStart indoors · Dec 17 – Dec 31
Broccoli, cabbageTransplant · Feb 4 – Feb 18
Onion setsPlant outdoors · Jan 28 – Feb 11
PotatoesPlant outdoors · Feb 4 – Feb 18
LettuceSow outdoors · Jan 28 – Feb 11
Carrots, beetsSow outdoors · Feb 4 – Feb 18
TomatoesStart indoors · Dec 31 – Jan 14
TomatoesTransplant · Mar 4 – Mar 18
Peppers, eggplantStart indoors · Dec 17 – Dec 31
Peppers, eggplantTransplant · Mar 11 – Mar 25
BeansSow outdoors · Mar 4 – Mar 18
Sweet cornSow outdoors · Mar 4 – Mar 18
Cucumbers, squashSow outdoors · Mar 4 – Mar 18
Fall lettuce, spinachSow outdoors · Sep 30 – Oct 14
GarlicPlant cloves · Nov 11 – Dec 16
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Feb 25) and first fall frost (Nov 25) 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 94028 came on Jan 26 — about the same time as the 1991–2020 average (Jan 27).

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 Portola Valley, CA

The soil mapped at the center of ZIP 94028 is Botella — loam, well drained.

TextureLoama good balance for most vegetables
pH8.2alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter4%moderate
Hydrologic groupCwater soaks in slowly
Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Botella loam, 0 to 5 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 94028; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Portola Valley, CA

Summer high89 °Faverage high, August
Winter low37 °Faverage low, December
Hot days55days a year at 90 °F or more
Freezing nights26nights a year at 32 °F or less
Growing degree days3,885base 50 °F — the season’s usable heat
Longest day14 h 44 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
Precipitation43.6 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°32 °FJanuary: average high 61 °F, low 38 °F 61°38° JanFebruary: average high 64 °F, low 40 °F 64°40° FebMarch: average high 69 °F, low 41 °F 69°41° MarApril: average high 73 °F, low 43 °F 73°43° AprMay: average high 78 °F, low 47 °F 78°47° MayJune: average high 84 °F, low 50 °F 84°50° JunJuly: average high 88 °F, low 53 °F 88°53° JulAugust: average high 89 °F, low 53 °F 89°53° AugSeptember: average high 87 °F, low 51 °F 87°51° SepOctober: average high 80 °F, low 46 °F 80°46° OctNovember: average high 68 °F, low 41 °F 68°41° NovDecember: average high 61 °F, low 37 °F 61°37° Dec

Precipitation by month inches

0″2″4″6″8″January: 7.37 in precipitation 7.4 JanFebruary: 7.36 in precipitation 7.4 FebMarch: 7.68 in precipitation 7.7 MarApril: 3.64 in precipitation 3.6 AprMay: 1.64 in precipitation 1.6 MayJune: 0.68 in precipitation 0.7 JunJuly: 0.01 in precipitation 0.0 JulAugust: 0.05 in precipitation 0.1 AugSeptember: 0.12 in precipitation 0.1 SepOctober: 2.06 in precipitation 2.1 OctNovember: 4.48 in precipitation 4.5 NovDecember: 8.53 in precipitation 8.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Woodside Fire Stn 1, CA (4 mi away); precipitation: Woodside 3.4 S, CA (3 mi away). 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.

943049b
Palo Alto, CA · 3 mi
943059b
Stanford, CA · 4 mi
940229b
Los Altos, CA · 4 mi
9406210a
Redwood City, CA · 5 mi
943069b
Palo Alto, CA · 5 mi
940239b
Los Altos, CA · 5 mi
940259b
Menlo Park, CA · 6 mi
940279b
Atherton, CA · 6 mi

California planting zones →

Questions about 94028

What planting zone is ZIP code 94028?

ZIP code 94028 (Portola 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).

When is the last frost in Portola Valley, CA?

The median last spring frost (32 °F) near 94028 is February 25; after April 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Woodside Fire Stn 1 station.

When is the first frost in Portola Valley, CA?

The median first fall frost near 94028 is November 25, giving a median frost-free growing season of 274 days.

When should I plant tomatoes in 94028?

Start tomato seeds indoors around Dec 31 – Jan 14 and set transplants outside around Mar 4 – Mar 18, one to three weeks after the median last frost.

How much rain and snow does 94028 get?

About 43.6 inches of precipitation a year (NOAA 1991–2020 normals, Woodside 3.4 S station).

How hot do summers get in Portola Valley, CA?

The average high peaks at 89 °F in August, with about 55 days a year at 90 °F or more.

What kind of soil does 94028 have?

The USDA soil survey maps Botella at the center of ZIP 94028: loam, well drained, pH about 8.2 (alkaline).

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

Spring leaf-out near 94028 came on Jan 26 in 2026, about the same as the 1991–2020 average (Jan 27), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Portola Valley, CA?

Intermediate onions: the longest day near 94028 is 14 h 44 min, so day-neutral types bulb best; long-day varieties may not bulb fully.