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

Planting zone for 94021 — Loma Mar, CA

ZIP code 94021 (Loma Mar, San Mateo County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F. The median last spring frost is March 21 and the first fall frost December 15.

Where ZIP 94021 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 frostMar 21
First frostDec 15
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 Loma Mar, 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 Loma Mar, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMarch 21median — 50% chance of a later frost
Safe for tender plantsApril 28only 10% chance of frost after
First fall frostDecember 15median — 10% chance by Nov 21
Growing season275 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 29 and returns around January 4.

From the NOAA station Skyline Ridge Preserve, CA — 6 miles away, elevation 2,270 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 94021

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Feb 7 – Feb 21
SpinachSow outdoors · Feb 7 – Feb 28
Broccoli, cabbageStart indoors · Jan 10 – Jan 24
Broccoli, cabbageTransplant · Feb 28 – Mar 14
Onion setsPlant outdoors · Feb 21 – Mar 7
PotatoesPlant outdoors · Feb 28 – Mar 14
LettuceSow outdoors · Feb 21 – Mar 7
Carrots, beetsSow outdoors · Feb 28 – Mar 14
TomatoesStart indoors · Jan 24 – Feb 7
TomatoesTransplant · Mar 28 – Apr 11
Peppers, eggplantStart indoors · Jan 10 – Jan 24
Peppers, eggplantTransplant · Apr 4 – Apr 18
BeansSow outdoors · Mar 28 – Apr 11
Sweet cornSow outdoors · Mar 28 – Apr 11
Cucumbers, squashSow outdoors · Mar 28 – Apr 11
Fall lettuce, spinachSow outdoors · Oct 20 – Nov 3
GarlicPlant cloves · Dec 1 – Jan 5
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 21) and first fall frost (Dec 15) 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 94021 came on Jan 19 — 9 days earlier than 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 Loma Mar, CA

The soil mapped at the center of ZIP 94021 is Hugo — sandy loam, well drained.

TextureSandy loamdrains and warms fast; dries out and needs more feeding
pH6.1slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2.5%moderate
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Hugo and Josephine sandy loams, very steep, eroded.

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 94021; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Loma Mar, CA

Summer high81 °Faverage high, July
Winter low40 °Faverage low, February
Hot days13days a year at 90 °F or more
Freezing nights11nights a year at 32 °F or less
Growing degree days3,234base 50 °F — the season’s usable heat
Longest day14 h 44 mindaylight on June 21
Shortest day9 h 36 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation42.2 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°32 °FJanuary: average high 55 °F, low 41 °F 55°41° JanFebruary: average high 55 °F, low 40 °F 55°40° FebMarch: average high 58 °F, low 41 °F 58°41° MarApril: average high 62 °F, low 43 °F 62°43° AprMay: average high 67 °F, low 47 °F 67°47° MayJune: average high 75 °F, low 52 °F 75°52° JunJuly: average high 81 °F, low 58 °F 81°58° JulAugust: average high 81 °F, low 59 °F 81°59° AugSeptember: average high 79 °F, low 57 °F 79°57° SepOctober: average high 71 °F, low 52 °F 71°52° OctNovember: average high 60 °F, low 44 °F 60°44° NovDecember: average high 54 °F, low 40 °F 54°40° Dec

Precipitation by month inches

0″2″4″6″8″January: 7.77 in precipitation 7.8 JanFebruary: 7.97 in precipitation 8.0 FebMarch: 6.32 in precipitation 6.3 MarApril: 3.37 in precipitation 3.4 AprMay: 1.29 in precipitation 1.3 MayJune: 0.42 in precipitation 0.4 JunJuly: 0.04 in precipitation 0.0 JulAugust: 0.11 in precipitation 0.1 AugSeptember: 0.18 in precipitation 0.2 SepOctober: 1.73 in precipitation 1.7 OctNovember: 4.60 in precipitation 4.6 NovDecember: 8.41 in precipitation 8.4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Skyline Ridge Preserve, CA (6 mi away); precipitation: Skyline Ridge Preserve, CA (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 9b.

940609b
Pescadero, CA · 1 mi
940209b
La Honda, CA · 2 mi
940749b
San Gregorio, CA · 8 mi
950069b
Boulder Creek, CA · 8 mi
940289b
Portola Valley, CA · 9 mi
940229b
Los Altos, CA · 9 mi
950149b
Cupertino, CA · 10 mi
940269b
Menlo Park, CA · 10 mi

California planting zones →

Questions about 94021

What planting zone is ZIP code 94021?

ZIP code 94021 (Loma Mar, 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 Loma Mar, CA?

The median last spring frost (32 °F) near 94021 is March 21; after April 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Skyline Ridge Preserve station.

When is the first frost in Loma Mar, CA?

The median first fall frost near 94021 is December 15, giving a median frost-free growing season of 275 days.

When should I plant tomatoes in 94021?

Start tomato seeds indoors around Jan 24 – Feb 7 and set transplants outside around Mar 28 – Apr 11, one to three weeks after the median last frost.

How much rain and snow does 94021 get?

About 42.2 inches of precipitation a year (NOAA 1991–2020 normals, Skyline Ridge Preserve station).

How hot do summers get in Loma Mar, CA?

The average high peaks at 81 °F in July, with about 13 days a year at 90 °F or more.

What kind of soil does 94021 have?

The USDA soil survey maps Hugo at the center of ZIP 94021: sandy loam, well drained, pH about 6.1 (slightly acidic).

Did spring come early in Loma Mar, CA in 2026?

Spring leaf-out near 94021 came on Jan 19 in 2026, 9 days earlier than the 1991–2020 average (Jan 28), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Loma Mar, CA?

Intermediate onions: the longest day near 94021 is 14 h 44 min, so day-neutral types bulb best; long-day varieties may not bulb fully.