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

Planting zone for 91118 — San Marino, CA

ZIP code 91118 (San Marino, Los Angeles County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F.

Where ZIP 91118 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.

Zone10a30 to 35 °F
Coldest night−1.1 to 1.7 °C
Last frostrare
First frostrare
2012 zone10a

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 10a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for San Marino, 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 San Gabriel Fire Dept, CA — 2 miles away, elevation 364 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 91118 came on Jan 17 — 3 days earlier than the 1991–2020 average (Jan 20).

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 San Marino, CA

The soil mapped at the center of ZIP 91118 is Azuvina — loam, well drained. Much of the area is built over (urban land); this is the natural soil underneath.

TextureLoama good balance for most vegetables
pH7.9alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2.5%moderate
Hydrologic groupCwater soaks in slowly
Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Urban land-Azuvina-Montebello complex, 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 91118; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in San Marino, CA

Summer high88 °Faverage high, August
Winter low45 °Faverage low, December
Hot days65days a year at 90 °F or more
Freezing nights1nights a year at 32 °F or less
Growing degree days5,861base 50 °F — the season’s usable heat
Longest day14 h 26 mindaylight on June 21
Shortest day9 h 52 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation18.6 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°32 °FJanuary: average high 69 °F, low 46 °F 69°46° JanFebruary: average high 68 °F, low 47 °F 68°47° FebMarch: average high 71 °F, low 51 °F 71°51° MarApril: average high 74 °F, low 53 °F 74°53° AprMay: average high 76 °F, low 58 °F 76°58° MayJune: average high 81 °F, low 62 °F 81°62° JunJuly: average high 86 °F, low 65 °F 86°65° JulAugust: average high 88 °F, low 66 °F 88°66° AugSeptember: average high 87 °F, low 64 °F 87°64° SepOctober: average high 81 °F, low 57 °F 81°57° OctNovember: average high 74 °F, low 51 °F 74°51° NovDecember: average high 68 °F, low 45 °F 68°45° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 4.20 in precipitation 4.2 JanFebruary: 4.77 in precipitation 4.8 FebMarch: 2.86 in precipitation 2.9 MarApril: 1.04 in precipitation 1.0 AprMay: 0.55 in precipitation 0.6 MayJune: 0.16 in precipitation 0.2 JunJuly: 0.06 in precipitation 0.1 JulAugust: 0.02 in precipitation 0.0 AugSeptember: 0.19 in precipitation 0.2 SepOctober: 0.75 in precipitation 0.8 OctNovember: 1.03 in precipitation 1.0 NovDecember: 2.94 in precipitation 2.9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: San Gabriel Fire Dept, CA (2 mi away); precipitation: Pasadena 2.0 Se, CA (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 10a.

9110810a
San Marino, CA · <1 mi
9177510a
San Gabriel, CA · 1 mi
9112510a
Pasadena, CA · 2 mi
9177810a
San Gabriel, CA · 2 mi
9110610a
Pasadena, CA · 2 mi
9180210a
Alhambra, CA · 2 mi
9180410a
Alhambra, CA · 2 mi
9189610a
Alhambra, CA · 2 mi

All 2 ZIP codes in San Marino → · California planting zones →

Questions about 91118

What planting zone is ZIP code 91118?

ZIP code 91118 (San Marino, CA) is in USDA hardiness zone 10a on the 2023 map: the coldest night of an average winter reaches 30 to 35 °F (−1.1 to 1.7 °C).

How much rain and snow does 91118 get?

About 18.6 inches of precipitation a year (NOAA 1991–2020 normals, Pasadena 2.0 Se station).

How hot do summers get in San Marino, CA?

The average high peaks at 88 °F in August, with about 65 days a year at 90 °F or more.

What kind of soil does 91118 have?

The USDA soil survey maps Azuvina at the center of ZIP 91118: loam, well drained, pH about 7.9 (alkaline).

Did spring come early in San Marino, CA in 2026?

Spring leaf-out near 91118 came on Jan 17 in 2026, 3 days earlier than the 1991–2020 average (Jan 20), according to the USA National Phenology Network Spring Index.

What kind of onions grow in San Marino, CA?

Intermediate onions: the longest day near 91118 is 14 h 26 min, so day-neutral types bulb best; long-day varieties may not bulb fully.