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

Planting zone for 93402 — Los Osos, CA

ZIP code 93402 (Los Osos, San Luis Obispo County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F.

Where ZIP 93402 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.

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 Los Osos, 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 Morro Bay Fire Dept, CA — 5 miles away, elevation 118 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 93402 came on Jan 19 — 6 days earlier than the 1991–2020 average (Jan 25).

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 Osos, CA

The soil mapped at the center of ZIP 93402 is Santa Lucia — channery clay loam, well drained.

TextureChannery clay loamholds water and nutrients; slow to drain and warm up
pH5.7moderately acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter6%high
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Santa Lucia channery clay loam, 50 to 75 percent slopes, MLRA 15.

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 93402; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Los Osos, CA

Summer high73 °Faverage high, October
Winter low46 °Faverage low, January
Hot days1days a year at 90 °F or more
Freezing nights3nights a year at 32 °F or less
Growing degree days3,512base 50 °F — the season’s usable heat
Longest day14 h 32 mindaylight on June 21
Shortest day9 h 46 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

40°50°60°70°80°January: average high 65 °F, low 46 °F 65°46° JanFebruary: average high 65 °F, low 48 °F 65°48° FebMarch: average high 66 °F, low 49 °F 66°49° MarApril: average high 67 °F, low 49 °F 67°49° AprMay: average high 67 °F, low 52 °F 67°52° MayJune: average high 66 °F, low 54 °F 66°54° JunJuly: average high 67 °F, low 57 °F 67°57° JulAugust: average high 70 °F, low 57 °F 70°57° AugSeptember: average high 72 °F, low 56 °F 72°56° SepOctober: average high 73 °F, low 54 °F 73°54° OctNovember: average high 69 °F, low 50 °F 69°50° NovDecember: average high 65 °F, low 46 °F 65°46° Dec

Precipitation by month inches

0″1″2″3″4″January: 3.64 in precipitation, 0.1 in snowfall 3.6 JanFebruary: 3.62 in precipitation 3.6 FebMarch: 3.19 in precipitation 3.2 MarApril: 0.99 in precipitation 1.0 AprMay: 0.42 in precipitation 0.4 MayJune: 0.20 in precipitation 0.2 JunJuly: 0.07 in precipitation 0.1 JulAugust: 0.02 in precipitation 0.0 AugSeptember: 0.09 in precipitation 0.1 SepOctober: 0.68 in precipitation 0.7 OctNovember: 1.33 in precipitation 1.3 NovDecember: 2.75 in precipitation 2.8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Morro Bay Fire Dept, CA (5 mi away); precipitation: Morro Bay Fire Dept, CA (5 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

9341210a
Los Osos, CA · 1 mi
9344310a
Morro Bay, CA · 5 mi
934059b
San Luis Obispo, CA · 6 mi
9340810a
San Luis Obispo, CA · 7 mi
9342410a
Avila Beach, CA · 7 mi
934429b
Morro Bay, CA · 8 mi
934099b
San Luis Obispo, CA · 8 mi
934079b
San Luis Obispo, CA · 9 mi

All 2 ZIP codes in Los Osos → · California planting zones →

Questions about 93402

What planting zone is ZIP code 93402?

ZIP code 93402 (Los Osos, 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 93402 get?

About 17 inches of precipitation a year (NOAA 1991–2020 normals, Morro Bay Fire Dept station).

How hot do summers get in Los Osos, CA?

The average high peaks at 73 °F in October, with about 1 days a year at 90 °F or more.

What kind of soil does 93402 have?

The USDA soil survey maps Santa Lucia at the center of ZIP 93402: channery clay loam, well drained, pH about 5.7 (moderately acidic).

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

Spring leaf-out near 93402 came on Jan 19 in 2026, 6 days earlier than the 1991–2020 average (Jan 25), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Los Osos, CA?

Intermediate onions: the longest day near 93402 is 14 h 32 min, so day-neutral types bulb best; long-day varieties may not bulb fully.