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

Planting zone for 92304 — Amboy, CA

ZIP code 92304 (Amboy, San Bernardino County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F. The median last spring frost is March 6 and the first fall frost December 8.

Where ZIP 92304 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.

Zone9b25 to 30 °F
Coldest night−3.9 to −1.1 °C
Last frostMar 6
First frostDec 8
2012 zone9b

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 9b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Amboy, 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 Amboy, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMarch 6median — 50% chance of a later frost
Safe for tender plantsApril 9only 10% chance of frost after
First fall frostDecember 8median — 10% chance by Nov 12
Growing season272 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 1 and returns around December 25.

From the NOAA station Mitchell Caverns, CA — 29 miles away, elevation 4,351 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 92304

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Jan 23 – Feb 6
SpinachSow outdoors · Jan 23 – Feb 13
Broccoli, cabbageStart indoors · Dec 26 – Jan 9
Broccoli, cabbageTransplant · Feb 13 – Feb 27
Onion setsPlant outdoors · Feb 6 – Feb 20
PotatoesPlant outdoors · Feb 13 – Feb 27
LettuceSow outdoors · Feb 6 – Feb 20
Carrots, beetsSow outdoors · Feb 13 – Feb 27
TomatoesStart indoors · Jan 9 – Jan 23
TomatoesTransplant · Mar 13 – Mar 27
Peppers, eggplantStart indoors · Dec 26 – Jan 9
Peppers, eggplantTransplant · Mar 20 – Apr 3
BeansSow outdoors · Mar 13 – Mar 27
Sweet cornSow outdoors · Mar 13 – Mar 27
Cucumbers, squashSow outdoors · Mar 13 – Mar 27
Fall lettuce, spinachSow outdoors · Oct 13 – Oct 27
GarlicPlant cloves · Nov 24 – Dec 29
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 6) and first fall frost (Dec 8) 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 92304 came on Jan 18 — 6 days earlier than the 1991–2020 average (Jan 24).

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 Amboy, CA

The soil mapped at the center of ZIP 92304 is Torriorthents — extremely gravelly sand, somewhat excessively drained.

TextureExtremely gravelly sanddrains and warms fast; dries out and needs more feeding
pH8.0alkaline; most vegetables like 6.0–7.0
DrainageSomewhat excessively drainednatural drainage class
Organic matter0.2%low — add compost
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Torriorthents, Torripsamments, and Haplargids; hyperthermic fan piedmonts.

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 92304; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Amboy, CA

Summer high92 °Faverage high, July
Winter low40 °Faverage low, January
Hot days71days a year at 90 °F or more
Freezing nights22nights a year at 32 °F or less
Growing degree days5,424base 50 °F — the season’s usable heat
Longest day14 h 28 mindaylight on June 21
Shortest day9 h 50 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation4.8 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°32 °FJanuary: average high 54 °F, low 40 °F 54°40° JanFebruary: average high 55 °F, low 41 °F 55°41° FebMarch: average high 62 °F, low 45 °F 62°45° MarApril: average high 68 °F, low 50 °F 68°50° AprMay: average high 77 °F, low 58 °F 77°58° MayJune: average high 87 °F, low 69 °F 87°69° JunJuly: average high 92 °F, low 73 °F 92°73° JulAugust: average high 91 °F, low 72 °F 91°72° AugSeptember: average high 85 °F, low 68 °F 85°68° SepOctober: average high 74 °F, low 57 °F 74°57° OctNovember: average high 62 °F, low 47 °F 62°47° NovDecember: average high 53 °F, low 40 °F 53°40° Dec

Precipitation by month inches

0″1″January: 0.96 in precipitation 1.0 JanFebruary: 0.78 in precipitation 0.8 FebMarch: 0.47 in precipitation 0.5 MarApril: 0.17 in precipitation 0.2 AprMay: 0.10 in precipitation 0.1 MayJune: 0.01 in precipitation 0.0 JunJuly: 0.29 in precipitation 0.3 JulAugust: 0.37 in precipitation 0.4 AugSeptember: 0.35 in precipitation 0.3 SepOctober: 0.31 in precipitation 0.3 OctNovember: 0.26 in precipitation 0.3 NovDecember: 0.71 in precipitation 0.7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Mitchell Caverns, CA (29 mi away); precipitation: Amboy, CA (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

5 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

922779b
Twentynine Palms, CA · 29 mi
922789b
Twentynine Palms, CA · 30 mi
923329a
Essex, CA · 31 mi
923389a
Ludlow, CA · 36 mi
922529a
Joshua Tree, CA · 44 mi
922869a
Yucca Valley, CA · 45 mi
923238b
Cima, CA · 49 mi
922809b
Vidal, CA · 50 mi

California planting zones →

Questions about 92304

What planting zone is ZIP code 92304?

ZIP code 92304 (Amboy, CA) is in USDA hardiness zone 9b on the 2023 map: the coldest night of an average winter reaches 25 to 30 °F (−3.9 to −1.1 °C).

When is the last frost in Amboy, CA?

The median last spring frost (32 °F) near 92304 is March 6; after April 9 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mitchell Caverns station.

When is the first frost in Amboy, CA?

The median first fall frost near 92304 is December 8, giving a median frost-free growing season of 272 days.

When should I plant tomatoes in 92304?

Start tomato seeds indoors around Jan 9 – Jan 23 and set transplants outside around Mar 13 – Mar 27, one to three weeks after the median last frost.

How much rain and snow does 92304 get?

About 4.8 inches of precipitation a year (NOAA 1991–2020 normals, Amboy station).

How hot do summers get in Amboy, CA?

The average high peaks at 92 °F in July, with about 71 days a year at 90 °F or more.

What kind of soil does 92304 have?

The USDA soil survey maps Torriorthents at the center of ZIP 92304: extremely gravelly sand, somewhat excessively drained, pH about 8.0 (alkaline).

Did spring come early in Amboy, CA in 2026?

Spring leaf-out near 92304 came on Jan 18 in 2026, 6 days earlier than the 1991–2020 average (Jan 24), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Amboy, CA?

Intermediate onions: the longest day near 92304 is 14 h 28 min, so day-neutral types bulb best; long-day varieties may not bulb fully.