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

Planting zone for 96789 — Mililani, HI

ZIP code 96789 (Mililani, Honolulu County) is in USDA zone 12a: the coldest winter night averages 50 to 55 °F.

Where ZIP 96789 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.

Zone12a50 to 55 °F
Coldest night10 to 12.8 °C
Last frostrare
First frostrare
2012 zone12a

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 12a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Mililani, HI…

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

Frost is rare or absent here: Mililani, HI is in zone 12a, where the coldest night of a typical winter stays above freezing. Cool-season vegetables grow best from fall through spring; summer heat, not frost, is the limit.

Native plants for zone 12a in Hawaii

37 plants native to Hawaii, recorded in Hawaii, and rated by the USDA to survive 50 °F or colder — the bottom of zone 12a. Each links to its USDA PLANTS profile.

Trees 7

Chamisso's manfern10 ft · blooms indeterminate · medium shade tolerance · to 40 °Fhapu'u8 ft · blooms indeterminate · medium shade tolerance · to 40 °FHawai'i pritchardia60 ft · medium shade tolerance · to 40 °FKamalo pritchardia16 ft · medium shade tolerance · to 40 °Fkoa110 ft · blooms spring · high shade tolerance · to 31 °Fkoaoha40 ft · blooms early spring · high shade tolerance · to 25 °F

Shrubs 12

'ala'a40 ft · medium shade tolerance · to 40 °F'ohi'a lehua65 ft · blooms late spring · high shade tolerance · to 22 °Fbeach naupaka10 ft · blooms indeterminate · medium shade tolerance · to 31 °FGaudichaud's senna2 ft · to 40 °FHawai'i desert-thorn1 ft · blooms summer · medium shade tolerance · to 40 °FHawai'i hawthorn12 ft · blooms spring · medium shade tolerance · to 35 °F

Wildflowers & perennials 8

bayhops1 ft · blooms indeterminate · medium shade tolerance · to 17 °Fbeach strawberry0.8 ft · blooms early spring · medium shade tolerance · to −33 °Fcommon duckmeatblooms late summer · medium shade tolerance · to −38 °Fcommon maidenhair1.7 ft · blooms summer · low shade tolerance · to −33 °Flongleaf pondweedblooms mid summer · high shade tolerance · to −38 °Fsalt heliotrope1.2 ft · blooms mid spring · high shade tolerance · to −28 °F

Grasses 10

blunt spikerush1.6 ft · blooms summer · high shade tolerance · to 37 °Fcosmopolitan bulrush3 ft · blooms late summer · high shade tolerance · to −23 °Ffragrant flatsedge2 ft · blooms late summer · high shade tolerance · to 42 °Fkawelu3 ft · high shade tolerance · to 40 °Fmanyspike flatsedge1.6 ft · blooms mid summer · high shade tolerance · to 47 °Fovate spikerush1.5 ft · blooms late summer · high shade tolerance · to 47 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Mililani, HI.

Soil in Mililani, HI

The soil mapped at the center of ZIP 96789 is Rough mountainous land — silty clay loam, well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH4.3strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter25%high
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Rough mountainous land.

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 96789; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mililani, HI

Summer high83 °Faverage high, August
Winter low60 °Faverage low, February
Hot days1days a year at 90 °F or more
Freezing nights0nights a year at 32 °F or less
Growing degree days7,985base 50 °F — the season’s usable heat
Longest day13 h 27 mindaylight on June 21
Shortest day10 h 49 mindaylight on December 21
Onions to growShort-daysummer days stay under about 14 h 20 min, so long-day varieties won’t bulb
Precipitation64.1 inper year, rain and melted snow

Average high and low, by month

50°60°70°80°90°January: average high 76 °F, low 61 °F 76°61° JanFebruary: average high 76 °F, low 60 °F 76°60° FebMarch: average high 77 °F, low 62 °F 77°62° MarApril: average high 77 °F, low 63 °F 77°63° AprMay: average high 79 °F, low 65 °F 79°65° MayJune: average high 80 °F, low 67 °F 80°67° JunJuly: average high 82 °F, low 67 °F 82°67° JulAugust: average high 83 °F, low 68 °F 83°68° AugSeptember: average high 83 °F, low 67 °F 83°67° SepOctober: average high 82 °F, low 66 °F 82°66° OctNovember: average high 79 °F, low 65 °F 79°65° NovDecember: average high 77 °F, low 63 °F 77°63° Dec

Precipitation by month inches

0″2″4″6″8″January: 5.18 in precipitation 5.2 JanFebruary: 4.31 in precipitation 4.3 FebMarch: 6.30 in precipitation 6.3 MarApril: 5.62 in precipitation 5.6 AprMay: 4.33 in precipitation 4.3 MayJune: 4.23 in precipitation 4.2 JunJuly: 5.17 in precipitation 5.2 JulAugust: 3.96 in precipitation 4.0 AugSeptember: 4.61 in precipitation 4.6 SepOctober: 5.76 in precipitation 5.8 OctNovember: 7.09 in precipitation 7.1 NovDecember: 7.52 in precipitation 7.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Upper Wahiawa 874.3, HI (5 mi away); precipitation: Upper Wahiawa 874.3, HI (5 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

9678212a
Pearl City, HI · 3 mi
9671712b
Hauula, HI · 5 mi
9670112a
Aiea, HI · 6 mi
9685412a
Wheeler Army Airfield, HI · 6 mi
9678612a
Wahiawa, HI · 7 mi
9673012b
Kaaawa, HI · 7 mi
9674412b
Kaneohe, HI · 7 mi
9679712a
Waipahu, HI · 7 mi

Hawaii planting zones →

Questions about 96789

What planting zone is ZIP code 96789?

ZIP code 96789 (Mililani, HI) is in USDA hardiness zone 12a on the 2023 map: the coldest night of an average winter reaches 50 to 55 °F (10 to 12.8 °C).

How much rain and snow does 96789 get?

About 64.1 inches of precipitation a year (NOAA 1991–2020 normals, Upper Wahiawa 874.3 station).

How hot do summers get in Mililani, HI?

The average high peaks at 83 °F in August, with about 1 days a year at 90 °F or more.

What kind of soil does 96789 have?

The USDA soil survey maps Rough mountainous land at the center of ZIP 96789: silty clay loam, well drained, pH about 4.3 (strongly acidic).

What kind of onions grow in Mililani, HI?

Short-day onions: the longest day near 96789 is 13 h 27 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.