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

Planting zone for 92346 — Highland, CA

ZIP code 92346 (Highland, San Bernardino County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F. The median last spring frost is January 27 and the first fall frost December 19.

Where ZIP 92346 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.

Zone10a30 to 35 °F
Coldest night−1.1 to 1.7 °C
Last frostJan 27
First frostDec 19
2012 zone9b

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 Service

Loading the forecast for Highland, 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 Highland, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostJanuary 27median — 50% chance of a later frost
Safe for tender plantsFebruary 28only 10% chance of frost after
First fall frostDecember 19median — 10% chance by Dec 1
Growing season329 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 7 and returns around January 1.

From the NOAA station Redlands, CA — 6 miles away, elevation 1,411 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 92346

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Dec 16 – Dec 30
SpinachSow outdoors · Dec 16 – Jan 6
Broccoli, cabbageStart indoors · Nov 18 – Dec 2
Broccoli, cabbageTransplant · Jan 6 – Jan 20
Onion setsPlant outdoors · Dec 30 – Jan 13
PotatoesPlant outdoors · Jan 6 – Jan 20
LettuceSow outdoors · Dec 30 – Jan 13
Carrots, beetsSow outdoors · Jan 6 – Jan 20
TomatoesStart indoors · Dec 2 – Dec 16
TomatoesTransplant · Feb 3 – Feb 17
Peppers, eggplantStart indoors · Nov 18 – Dec 2
Peppers, eggplantTransplant · Feb 10 – Feb 24
BeansSow outdoors · Feb 3 – Feb 17
Sweet cornSow outdoors · Feb 3 – Feb 17
Cucumbers, squashSow outdoors · Feb 3 – Feb 17
Fall lettuce, spinachSow outdoors · Oct 24 – Nov 7
GarlicPlant cloves · Dec 5 – Jan 9
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jan 27) and first fall frost (Dec 19) 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 92346 came on Jan 18 — 5 days earlier than the 1991–2020 average (Jan 23).

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 Highland, CA

The soil mapped at the center of ZIP 92346 is Greenfield — fine sandy loam, well drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding
pH6.7neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter0.75%low — add compost
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Greenfield fine sandy loam, 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 92346; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Highland, CA

Summer high96 °Faverage high, August
Winter low40 °Faverage low, December
Hot days104days a year at 90 °F or more
Freezing nights3nights a year at 32 °F or less
Growing degree days5,663base 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
Precipitation12.9 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 67 °F, low 41 °F 67°41° JanFebruary: average high 67 °F, low 42 °F 67°42° FebMarch: average high 71 °F, low 45 °F 71°45° MarApril: average high 76 °F, low 48 °F 76°48° AprMay: average high 80 °F, low 52 °F 80°52° MayJune: average high 89 °F, low 56 °F 89°56° JunJuly: average high 95 °F, low 63 °F 95°63° JulAugust: average high 96 °F, low 63 °F 96°63° AugSeptember: average high 92 °F, low 60 °F 92°60° SepOctober: average high 83 °F, low 53 °F 83°53° OctNovember: average high 75 °F, low 45 °F 75°45° NovDecember: average high 67 °F, low 40 °F 67°40° Dec

Precipitation by month inches

0″1″2″3″January: 2.76 in precipitation 2.8 JanFebruary: 2.99 in precipitation 3.0 FebMarch: 2.01 in precipitation 2.0 MarApril: 0.91 in precipitation 0.9 AprMay: 0.35 in precipitation 0.3 MayJune: 0.10 in precipitation 0.1 JunJuly: 0.10 in precipitation 0.1 JulAugust: 0.09 in precipitation 0.1 AugSeptember: 0.13 in precipitation 0.1 SepOctober: 0.53 in precipitation 0.5 OctNovember: 0.89 in precipitation 0.9 NovDecember: 2.01 in precipitation 2.0 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Redlands, CA (6 mi away); precipitation: Redlands, CA (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 10a.

9236910a
Patton, CA · 3 mi
9237410a
Redlands, CA · 4 mi
9237510a
Redlands, CA · 5 mi
9241010a
San Bernardino, CA · 5 mi
9240410a
San Bernardino, CA · 5 mi
9240810a
San Bernardino, CA · 6 mi
9235910a
Mentone, CA · 6 mi
9240210a
San Bernardino, CA · 7 mi

California planting zones →

Questions about 92346

What planting zone is ZIP code 92346?

ZIP code 92346 (Highland, 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).

When is the last frost in Highland, CA?

The median last spring frost (32 °F) near 92346 is January 27; after February 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Redlands station.

When is the first frost in Highland, CA?

The median first fall frost near 92346 is December 19, giving a median frost-free growing season of 329 days.

When should I plant tomatoes in 92346?

Start tomato seeds indoors around Dec 2 – Dec 16 and set transplants outside around Feb 3 – Feb 17, one to three weeks after the median last frost.

How much rain and snow does 92346 get?

About 12.9 inches of precipitation a year (NOAA 1991–2020 normals, Redlands station).

How hot do summers get in Highland, CA?

The average high peaks at 96 °F in August, with about 104 days a year at 90 °F or more.

What kind of soil does 92346 have?

The USDA soil survey maps Greenfield at the center of ZIP 92346: fine sandy loam, well drained, pH about 6.7 (neutral).

Did spring come early in Highland, CA in 2026?

Spring leaf-out near 92346 came on Jan 18 in 2026, 5 days earlier than the 1991–2020 average (Jan 23), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Highland, CA?

Intermediate onions: the longest day near 92346 is 14 h 26 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 92346 change?

Yes. The 2012 USDA map put 92346 in zone 9b; the 2023 map puts it in zone 10a. The newer map uses 1991–2020 data and more weather stations.