Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for Rialto, CA

Rialto, CA is in USDA zone 10a across its 2 ZIP codes.

Rialto on the zone map

Outlined: its 2 ZIP code areas · 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

ZIP codes2

Last frostrare

First frostrare

Growing seasonall year

10a 2 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

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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, 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 92377 came on Jan 16 — 6 days earlier than the 1991–2020 average (Jan 22).

average
Jan 222026
Jan 16

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 Rialto, CA

The soil mapped at the center of ZIP 92377 is Soboba — gravelly loamy sand, excessively drained.

TextureGravelly loamy sanddrains and warms fast; dries out and needs more feeding

pH6.3slightly acidic; most vegetables like 6.0–7.0

DrainageExcessively drainednatural drainage class

Organic matter0.75%low — add compost

Hydrologic groupAwater soaks in fast

Farmland classNot prime farmlandUSDA classification

Map unit: Soboba gravelly loamy sand, 0 to 9 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 92377; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Rialto, CA

Summer high97 °Faverage high, August

Winter low43 °Faverage low, December

Hot days103days a year at 90 °F or more

Freezing nights2nights a year at 32 °F or less

Growing degree days6,087base 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

Precipitation17.3 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Riverside Citrus Exp, CA (13 mi away); precipitation: Rialto 2.1 N, CA (within 1 mile). Daylight is calculated from latitude.