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

Planting zone for 91765 — Diamond Bar, CA

ZIP code 91765 (Diamond Bar, Los Angeles County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F.

Where ZIP 91765 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 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 Diamond Bar, 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 Pomona/Fairplex, CA — 7 miles away, elevation 1,001 ft) the median growing season is 354 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 91765 came on Jan 17 — 5 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 Diamond Bar, CA

The soil mapped at the center of ZIP 91765 is Apollo — clay loam, well drained.

TextureClay loamholds water and nutrients; slow to drain and warm up
pH8.2alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2.5%moderate
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Apollo, warm-Calleguas complex, 20 to 65 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 91765; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Diamond Bar, CA

Summer high92 °Faverage high, August
Winter low42 °Faverage low, December
Hot days71days a year at 90 °F or more
Freezing nights3nights a year at 32 °F or less
Growing degree days5,557base 50 °F — the season’s usable heat
Longest day14 h 25 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
Precipitation16.3 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°32 °FJanuary: average high 68 °F, low 43 °F 68°43° JanFebruary: average high 67 °F, low 45 °F 67°45° FebMarch: average high 72 °F, low 47 °F 72°47° MarApril: average high 76 °F, low 50 °F 76°50° AprMay: average high 78 °F, low 54 °F 78°54° MayJune: average high 84 °F, low 57 °F 84°57° JunJuly: average high 90 °F, low 62 °F 90°62° JulAugust: average high 92 °F, low 63 °F 92°63° AugSeptember: average high 89 °F, low 60 °F 89°60° SepOctober: average high 81 °F, low 54 °F 81°54° OctNovember: average high 74 °F, low 47 °F 74°47° NovDecember: average high 67 °F, low 42 °F 67°42° Dec

Precipitation by month inches

0″1″2″3″4″January: 3.30 in precipitation 3.3 JanFebruary: 3.88 in precipitation 3.9 FebMarch: 2.79 in precipitation 2.8 MarApril: 0.78 in precipitation 0.8 AprMay: 0.43 in precipitation 0.4 MayJune: 0.12 in precipitation 0.1 JunJuly: 0.07 in precipitation 0.1 JulAugust: 0.03 in precipitation 0.0 AugSeptember: 0.12 in precipitation 0.1 SepOctober: 0.85 in precipitation 0.8 OctNovember: 1.00 in precipitation 1.0 NovDecember: 2.94 in precipitation 2.9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Pomona/Fairplex, CA (7 mi away); precipitation: Diamond Bar 1.9 Nne, CA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 10a.

9178910a
Walnut, CA · 3 mi
9178810a
Walnut, CA · 4 mi
9282310a
Brea, CA · 4 mi
9282110a
Brea, CA · 4 mi
9176610a
Pomona, CA · 5 mi
9174810a
Rowland Heights, CA · 5 mi
9176810a
Pomona, CA · 6 mi
9170910a
Chino Hills, CA · 6 mi

California planting zones →

Questions about 91765

What planting zone is ZIP code 91765?

ZIP code 91765 (Diamond Bar, 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 91765 get?

About 16.3 inches of precipitation a year (NOAA 1991–2020 normals, Diamond Bar 1.9 Nne station).

How hot do summers get in Diamond Bar, CA?

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

What kind of soil does 91765 have?

The USDA soil survey maps Apollo at the center of ZIP 91765: clay loam, well drained, pH about 8.2 (alkaline).

Did spring come early in Diamond Bar, CA in 2026?

Spring leaf-out near 91765 came on Jan 17 in 2026, 5 days earlier than the 1991–2020 average (Jan 22), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Diamond Bar, CA?

Intermediate onions: the longest day near 91765 is 14 h 25 min, so day-neutral types bulb best; long-day varieties may not bulb fully.