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

Planting zone for 92331 — Fontana, CA

ZIP code 92331 (Fontana, Imperial County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F.

Where ZIP 92331 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 Fontana, 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 Ontario Intl Airport, CA — 8 miles away, elevation 948 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 92331 came on Jan 16 — 6 days earlier than the 1991–2020 average (Jan 22).

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 Fontana, CA

The soil mapped at the center of ZIP 92331 is Tujunga — gravelly loamy sand, somewhat excessively drained.

TextureGravelly loamy sanddrains and warms fast; dries out and needs more feeding
pH6.7neutral; most vegetables like 6.0–7.0
DrainageSomewhat excessively drainednatural drainage class
Organic matter0.75%low — add compost
Hydrologic groupAwater soaks in fast
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Tujunga 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 92331; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Fontana, CA

Summer high95 °Faverage high, August
Winter low44 °Faverage low, December
Hot days93days a year at 90 °F or more
Freezing nights2nights a year at 32 °F or less
Growing degree days6,189base 50 °F — the season’s usable heat
Longest day14 h 26 mindaylight on June 21
Shortest day9 h 53 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

30°40°50°60°70°80°90°100°110°32 °FJanuary: average high 68 °F, low 45 °F 68°45° JanFebruary: average high 68 °F, low 46 °F 68°46° FebMarch: average high 72 °F, low 49 °F 72°49° MarApril: average high 76 °F, low 51 °F 76°51° AprMay: average high 80 °F, low 56 °F 80°56° MayJune: average high 86 °F, low 60 °F 86°60° JunJuly: average high 94 °F, low 65 °F 94°65° JulAugust: average high 95 °F, low 65 °F 95°65° AugSeptember: average high 91 °F, low 64 °F 91°64° SepOctober: average high 83 °F, low 57 °F 83°57° OctNovember: average high 75 °F, low 49 °F 75°49° NovDecember: average high 67 °F, low 44 °F 67°44° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.59 in precipitation 3.6 JanFebruary: 4.19 in precipitation 4.2 FebMarch: 2.49 in precipitation 2.5 MarApril: 0.90 in precipitation 0.9 AprMay: 0.52 in precipitation 0.5 MayJune: 0.10 in precipitation 0.1 JunJuly: 0.11 in precipitation 0.1 JulAugust: 0.31 in precipitation 0.3 AugSeptember: 0.20 in precipitation 0.2 SepOctober: 0.69 in precipitation 0.7 OctNovember: 1.24 in precipitation 1.2 NovDecember: 2.99 in precipitation 3.0 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Ontario Intl Airport, CA (8 mi away); precipitation: Rialto 2.1 N, CA (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 10a.

9233510a
Fontana, CA · <1 mi
9233410a
Fontana, CA · 1 mi
9233710a
Fontana, CA · 3 mi
9233610a
Fontana, CA · 3 mi
9231610a
Bloomington, CA · 5 mi
9237610a
Rialto, CA · 5 mi
9237710a
Rialto, CA · 5 mi
9173910a
Rancho Cucamonga, CA · 5 mi

All 5 ZIP codes in Fontana → · California planting zones →

Questions about 92331

What planting zone is ZIP code 92331?

ZIP code 92331 (Fontana, 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 92331 get?

About 17.3 inches of precipitation a year (NOAA 1991–2020 normals, Rialto 2.1 N station).

How hot do summers get in Fontana, CA?

The average high peaks at 95 °F in August, with about 93 days a year at 90 °F or more.

What kind of soil does 92331 have?

The USDA soil survey maps Tujunga at the center of ZIP 92331: gravelly loamy sand, somewhat excessively drained, pH about 6.7 (neutral).

Did spring come early in Fontana, CA in 2026?

Spring leaf-out near 92331 came on Jan 16 in 2026, 6 days earlier than the 1991–2020 average (Jan 22), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Fontana, CA?

Intermediate onions: the longest day near 92331 is 14 h 26 min, so day-neutral types bulb best; long-day varieties may not bulb fully.