Planting zone for 93403 — San Luis Obispo, CA
ZIP code 93403 (San Luis Obispo, San Luis Obispo County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F.
Where ZIP 93403 is
tap the map for the zone at any spot · scroll or pinch to zoomNot 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.
Was 9b on the 2012 map — half a zone warmer now. 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 ServiceLoading the forecast for San Luis Obispo, 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 Luis Obispo Poly, CA — 2 miles away, elevation 308 ft) the median growing season is 349 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 93403 came on Jan 19 — 6 days earlier than the 1991–2020 average (Jan 25).
Jan 252026
Jan 19
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 Luis Obispo, CA
The soil mapped at the center of ZIP 93403 is Los Osos — loam, well drained.
Map unit: Los Osos-Diablo complex, 9 to 15 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 93403; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.
Climate in San Luis Obispo, CA
Average high and low, by month
Precipitation by month inches
NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: San Luis Obispo Poly, CA (2 mi away); precipitation: San Luis Obispo Poly, CA (2 mi away). Daylight is calculated from latitude.
Nearby ZIP codes
5 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.
All 8 ZIP codes in San Luis Obispo → · California planting zones →
Questions about 93403
What planting zone is ZIP code 93403?
ZIP code 93403 (San Luis Obispo, 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 93403 get?
About 22.4 inches of precipitation a year (NOAA 1991–2020 normals, San Luis Obispo Poly station).
How hot do summers get in San Luis Obispo, CA?
The average high peaks at 80 °F in August, with about 19 days a year at 90 °F or more.
What kind of soil does 93403 have?
The USDA soil survey maps Los Osos at the center of ZIP 93403: loam, well drained, pH about 6.5 (neutral).
Did spring come early in San Luis Obispo, CA in 2026?
Spring leaf-out near 93403 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 San Luis Obispo, CA?
Intermediate onions: the longest day near 93403 is 14 h 32 min, so day-neutral types bulb best; long-day varieties may not bulb fully.
Did the zone for 93403 change?
Yes. The 2012 USDA map put 93403 in zone 9b; the 2023 map puts it in zone 10a. The newer map uses 1991–2020 data and more weather stations.