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

Planting zone for 85371 — Poston, AZ

ZIP code 85371 (Poston, La Paz County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F.

Where ZIP 85371 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.

Zone9a20 to 25 °F
Coldest night−6.7 to −3.9 °C
Last frostrare
First frostrare
2012 zone9b

Was 9b 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 9a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Poston, AZ…

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 Parker, AZ — 14 miles away, elevation 420 ft) the median growing season is 338 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 85371 came on Jan 23 — about the same time as 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).

Native plants for zone 9a in Arizona

492 plants native to the lower 48 states, recorded in Arizona, and rated by the USDA to survive 20 °F or colder — the bottom of zone 9a. Each links to its USDA PLANTS profile.

Trees 26

Arizona cypress50 ft · blooms spring · low shade tolerance · to −23 °FArizona madrone30 ft · blooms late spring · high shade tolerance · to −4 °FArizona sycamore80 ft · blooms early spring · high shade tolerance · to −8 °FArizona walnut50 ft · blooms late spring · high shade tolerance · to −33 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °Fblue spruce100 ft · blooms late spring · medium shade tolerance · to −38 °F

Shrubs 109

alderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °FAmerican plum24 ft · blooms mid spring · high shade tolerance · to −38 °FAmerican tarwort3 ft · blooms late spring · high shade tolerance · to −23 °Fantelope bitterbrush6 ft · blooms early spring · medium shade tolerance · to −36 °FApache plume6 ft · blooms late spring · high shade tolerance · to −23 °Fbig sagebrush4 ft · blooms mid summer · high shade tolerance · to −43 °F

Wildflowers & perennials 197

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °FAmerican century plant6 ft · blooms indeterminate · high shade tolerance · to 12 °F

Grasses 151

alkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Fanalogue sedge1.5 ft · blooms late spring · medium shade tolerance · to −38 °FArizona cottontop4 ft · blooms late summer · high shade tolerance · to −13 °FArizona fescue2 ft · blooms late spring · high shade tolerance · to −23 °F

Vines 1

western white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °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 Poston, AZ.

Soil in Poston, AZ

The soil mapped at the center of ZIP 85371 is Kofa — 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 matter0.75%low — add compost
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Kofa clay loam, strongly saline, 0 to 3 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 85371; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Poston, AZ

Summer high108 °Faverage high, July
Winter low40 °Faverage low, December
Hot days185days a year at 90 °F or more
Freezing nights4nights a year at 32 °F or less
Growing degree days8,880base 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
Precipitation4.6 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°110°120°32 °FJanuary: average high 69 °F, low 42 °F 69°42° JanFebruary: average high 73 °F, low 45 °F 73°45° FebMarch: average high 80 °F, low 50 °F 80°50° MarApril: average high 87 °F, low 56 °F 87°56° AprMay: average high 96 °F, low 64 °F 96°64° MayJune: average high 105 °F, low 74 °F 105°74° JunJuly: average high 108 °F, low 81 °F 108°81° JulAugust: average high 108 °F, low 81 °F 108°81° AugSeptember: average high 103 °F, low 74 °F 103°74° SepOctober: average high 90 °F, low 61 °F 90°61° OctNovember: average high 78 °F, low 49 °F 78°49° NovDecember: average high 67 °F, low 40 °F 67°40° Dec

Precipitation by month inches

0″1″January: 0.85 in precipitation 0.8 JanFebruary: 0.73 in precipitation 0.7 FebMarch: 0.55 in precipitation 0.6 MarApril: 0.16 in precipitation 0.2 AprMay: 0.07 in precipitation 0.1 MayJune: 0.03 in precipitation 0.0 JunJuly: 0.18 in precipitation 0.2 JulAugust: 0.43 in precipitation 0.4 AugSeptember: 0.41 in precipitation 0.4 SepOctober: 0.42 in precipitation 0.4 OctNovember: 0.23 in precipitation 0.2 NovDecember: 0.51 in precipitation 0.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Parker, AZ (14 mi away); precipitation: Parker, AZ (14 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

853449b
Parker, AZ · 9 mi
922429b
Earp, CA · 16 mi
853599b
Quartzsite, AZ · 22 mi
922259b
Blythe, CA · 23 mi
9226710a
Parker Dam, CA · 25 mi
853349b
Ehrenberg, AZ · 26 mi
853469a
Quartzsite, AZ · 28 mi
922269b
Blythe, CA · 30 mi

Arizona planting zones →

Questions about 85371

What planting zone is ZIP code 85371?

ZIP code 85371 (Poston, AZ) is in USDA hardiness zone 9a on the 2023 map: the coldest night of an average winter reaches 20 to 25 °F (−6.7 to −3.9 °C).

How much rain and snow does 85371 get?

About 4.6 inches of precipitation a year (NOAA 1991–2020 normals, Parker station).

How hot do summers get in Poston, AZ?

The average high peaks at 108 °F in July, with about 185 days a year at 90 °F or more.

What kind of soil does 85371 have?

The USDA soil survey maps Kofa at the center of ZIP 85371: clay loam, well drained, pH about 8.2 (alkaline).

Did spring come early in Poston, AZ in 2026?

Spring leaf-out near 85371 came on Jan 23 in 2026, about the same as the 1991–2020 average (Jan 23), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Poston, AZ?

Intermediate onions: the longest day near 85371 is 14 h 25 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 85371 change?

Yes. The 2012 USDA map put 85371 in zone 9b; the 2023 map puts it in zone 9a. The newer map uses 1991–2020 data and more weather stations.