Planting zone for 92521 — Riverside, CA
ZIP code 92521 (Riverside, Riverside County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F.
Where ZIP 92521 is
Outlined: the ZIP code area · 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 Riverside, 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 Riverside Citrus Exp, CA — 2 miles away, elevation 988 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 92521 came on Jan 17 — 6 days earlier than the 1991–2020 average (Jan 23).
Jan 232026
Jan 17
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 Riverside, CA
The soil mapped at the center of ZIP 92521 is Cieneba — sandy loam, somewhat excessively drained.
Map unit: Cieneba rocky sandy loam, 15 to 50 percent slopes, 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 92521; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.
Climate in Riverside, CA
Average high and low, by month
Precipitation by month inches
NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Riverside Citrus Exp, CA (2 mi away); precipitation: Riverside Citrus Exp, CA (2 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.
All 16 ZIP codes in Riverside → · California planting zones →
Questions about 92521
What planting zone is ZIP code 92521?
ZIP code 92521 (Riverside, 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 92521 get?
About 9.9 inches of precipitation a year (NOAA 1991–2020 normals, Riverside Citrus Exp station).
How hot do summers get in Riverside, CA?
The average high peaks at 97 °F in August, with about 103 days a year at 90 °F or more.
What kind of soil does 92521 have?
The USDA soil survey maps Cieneba at the center of ZIP 92521: sandy loam, somewhat excessively drained, pH about 6.2 (slightly acidic).
Did spring come early in Riverside, CA in 2026?
Spring leaf-out near 92521 came on Jan 17 in 2026, 6 days earlier than the 1991–2020 average (Jan 23), according to the USA National Phenology Network Spring Index.
What kind of onions grow in Riverside, CA?
Intermediate onions: the longest day near 92521 is 14 h 25 min, so day-neutral types bulb best; long-day varieties may not bulb fully.
Did the zone for 92521 change?
Yes. The 2012 USDA map put 92521 in zone 9b; the 2023 map puts it in zone 10a. The newer map uses 1991–2020 data and more weather stations.