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

Planting zone for 92378 — Rimforest, CA

ZIP code 92378 (Rimforest, San Bernardino County) is in USDA zone 8a: the coldest winter night averages 10 to 15 °F. The median last spring frost is May 5 and the first fall frost November 2.

Where ZIP 92378 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.

Zone8a10 to 15 °F
Coldest night−12.2 to −9.4 °C
Last frostMay 5
First frostNov 2
2012 zone8b

Was 8b on the 2012 map — half a zone colder now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 8a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Rimforest, 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 in Rimforest, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 5median — 50% chance of a later frost
Safe for tender plantsMay 31only 10% chance of frost after
First fall frostNovember 2median — 10% chance by Oct 12
Growing season176 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 11 and returns around November 16.

From the NOAA station Lake Arrowhead, CA — 2 miles away, elevation 5,207 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 92378

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 24 – Apr 7
SpinachSow outdoors · Mar 24 – Apr 14
Broccoli, cabbageStart indoors · Feb 24 – Mar 10
Broccoli, cabbageTransplant · Apr 14 – Apr 28
Onion setsPlant outdoors · Apr 7 – Apr 21
PotatoesPlant outdoors · Apr 14 – Apr 28
LettuceSow outdoors · Apr 7 – Apr 21
Carrots, beetsSow outdoors · Apr 14 – Apr 28
TomatoesStart indoors · Mar 10 – Mar 24
TomatoesTransplant · May 12 – May 26
Peppers, eggplantStart indoors · Feb 24 – Mar 10
Peppers, eggplantTransplant · May 19 – Jun 2
BeansSow outdoors · May 12 – May 26
Sweet cornSow outdoors · May 12 – May 26
Cucumbers, squashSow outdoors · May 12 – May 26
Fall lettuce, spinachSow outdoors · Sep 7 – Sep 21
GarlicPlant cloves · Oct 19 – Nov 23
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 5) and first fall frost (Nov 2) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 92378 came on Feb 4 — 21 days earlier than the 1991–2020 average (Feb 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 Rimforest, CA

The soil mapped at the center of ZIP 92378 is Cedarpines — cobbly sandy loam, well drained.

TextureCobbly sandy loamdrains and warms fast; dries out and needs more feeding
pH6.4slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3%moderate
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Cedarpines-Stargazer-Urban land complex, 15 to 30 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 92378; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Rimforest, CA

Summer high82 °Faverage high, August
Winter low29 °Faverage low, January
Hot days11days a year at 90 °F or more
Freezing nights105nights a year at 32 °F or less
Growing degree days2,367base 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
Precipitation37.7 inper year, rain and melted snow
Snowfall22 inper year

Average high and low, by month

20°30°40°50°60°70°80°90°32 °FJanuary: average high 44 °F, low 29 °F 44°29° JanFebruary: average high 45 °F, low 30 °F 45°30° FebMarch: average high 52 °F, low 32 °F 52°32° MarApril: average high 60 °F, low 36 °F 60°36° AprMay: average high 67 °F, low 41 °F 67°41° MayJune: average high 76 °F, low 49 °F 76°49° JunJuly: average high 81 °F, low 57 °F 81°57° JulAugust: average high 82 °F, low 57 °F 82°57° AugSeptember: average high 74 °F, low 52 °F 74°52° SepOctober: average high 63 °F, low 43 °F 63°43° OctNovember: average high 52 °F, low 34 °F 52°34° NovDecember: average high 43 °F, low 29 °F 43°29° Dec

Precipitation by month inches · ❄ = snowfall

0″2″4″6″8″10″January: 8.36 in precipitation, 3 in snowfall 8.4❄3 JanFebruary: 9.87 in precipitation, 5.3 in snowfall 9.9❄5 FebMarch: 5.17 in precipitation, 6.7 in snowfall 5.2❄7 MarApril: 2.76 in precipitation, 2.8 in snowfall 2.8❄3 AprMay: 1.15 in precipitation, 0.8 in snowfall 1.1❄1 MayJune: 0.26 in precipitation 0.3 JunJuly: 0.12 in precipitation 0.1 JulAugust: 0.13 in precipitation 0.1 AugSeptember: 0.31 in precipitation 0.3 SepOctober: 2.06 in precipitation 2.1 OctNovember: 2.37 in precipitation, 0.3 in snowfall 2.4 NovDecember: 5.17 in precipitation, 3.5 in snowfall 5.2❄4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Lake Arrowhead, CA (2 mi away); precipitation: Lake Arrowhead, CA (2 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.

923918a
Twin Peaks, CA · <1 mi
923178a
Blue Jay, CA · 1 mi
923858a
Skyforest, CA · 1 mi
923258b
Crestline, CA · 3 mi
923528b
Lake Arrowhead, CA · 3 mi
9240410a
San Bernardino, CA · 4 mi
923218a
Cedar Glen, CA · 5 mi
923228b
Cedarpines Park, CA · 6 mi

California planting zones →

Questions about 92378

What planting zone is ZIP code 92378?

ZIP code 92378 (Rimforest, CA) is in USDA hardiness zone 8a on the 2023 map: the coldest night of an average winter reaches 10 to 15 °F (−12.2 to −9.4 °C).

When is the last frost in Rimforest, CA?

The median last spring frost (32 °F) near 92378 is May 5; after May 31 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Lake Arrowhead station.

When is the first frost in Rimforest, CA?

The median first fall frost near 92378 is November 2, giving a median frost-free growing season of 176 days.

When should I plant tomatoes in 92378?

Start tomato seeds indoors around Mar 10 – Mar 24 and set transplants outside around May 12 – May 26, one to three weeks after the median last frost.

How much rain and snow does 92378 get?

About 37.7 inches of precipitation a year and 22 inches of snowfall (NOAA 1991–2020 normals, Lake Arrowhead station).

How hot do summers get in Rimforest, CA?

The average high peaks at 82 °F in August, with about 11 days a year at 90 °F or more.

What kind of soil does 92378 have?

The USDA soil survey maps Cedarpines at the center of ZIP 92378: cobbly sandy loam, well drained, pH about 6.4 (slightly acidic).

Did spring come early in Rimforest, CA in 2026?

Spring leaf-out near 92378 came on Feb 4 in 2026, 21 days earlier than the 1991–2020 average (Feb 25), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Rimforest, CA?

Intermediate onions: the longest day near 92378 is 14 h 26 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 92378 change?

Yes. The 2012 USDA map put 92378 in zone 8b; the 2023 map puts it in zone 8a. The newer map uses 1991–2020 data and more weather stations.