Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 85618 — Mammoth, AZ

ZIP code 85618 (Mammoth, Pinal County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F. The median last spring frost is March 29 and the first fall frost November 13.

Where ZIP 85618 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 frostMar 29

First frostNov 13

2012 zone9a

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 9a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Mammoth, 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 in Mammoth, AZ

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMarch 29median — 50% chance of a later frost

Safe for tender plantsApril 29only 10% chance of frost after

First fall frostNovember 13median — 10% chance by Oct 26

Growing season225 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 9 and returns around November 24.

From the NOAA station Oracle Sp, AZ — 12 miles away, elevation 4,597 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 85618

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 15 – Mar 1

SpinachSow outdoors · Feb 15 – Mar 8

Broccoli, cabbageStart indoors · Jan 18 – Feb 1

Broccoli, cabbageTransplant · Mar 8 – Mar 22

Onion setsPlant outdoors · Mar 1 – Mar 15

PotatoesPlant outdoors · Mar 8 – Mar 22

LettuceSow outdoors · Mar 1 – Mar 15

Carrots, beetsSow outdoors · Mar 8 – Mar 22

TomatoesStart indoors · Feb 1 – Feb 15

TomatoesTransplant · Apr 5 – Apr 19

Peppers, eggplantStart indoors · Jan 18 – Feb 1

Peppers, eggplantTransplant · Apr 12 – Apr 26

BeansSow outdoors · Apr 5 – Apr 19

Sweet cornSow outdoors · Apr 5 – Apr 19

Cucumbers, squashSow outdoors · Apr 5 – Apr 19

Fall lettuce, spinachSow outdoors · Sep 18 – Oct 2

GarlicPlant cloves · Oct 30 – Dec 4

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 29) and first fall frost (Nov 13) 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 85618 came on Jan 27 — about the same time as the 1991–2020 average (Jan 28).

average
Jan 282026
Jan 27

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.

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 Mammoth, AZ.

Soil in Mammoth, AZ

The soil mapped at the center of ZIP 85618 is Stagecoach — extremely cobbly sandy loam, somewhat excessively drained.

TextureExtremely cobbly sandy loamdrains and warms fast; dries out and needs more feeding

pH7.6slightly alkaline; most vegetables like 6.0–7.0

DrainageSomewhat excessively drainednatural drainage class

Organic matter0.8%low — add compost

Hydrologic groupAwater soaks in fast

Farmland classNot prime farmlandUSDA classification

Map unit: Stagecoach-Delnorte complex, 5 to 45 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 85618; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mammoth, AZ

Summer high94 °Faverage high, June

Winter low31 °Faverage low, January

Hot days94days a year at 90 °F or more

Freezing nights59nights a year at 32 °F or less

Growing degree days5,061base 50 °F — the season’s usable heat

Longest day14 h 19 mindaylight on June 21

Shortest day9 h 59 mindaylight on December 21

Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully

Precipitation15.6 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Oracle Sp, AZ (12 mi away); precipitation: Oracle Sp, AZ (12 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

856239a

Oracle, AZ · 10 mi

851929a

Winkelman, AZ · 13 mi

856319a

San Manuel, AZ · 16 mi

Mount Lemmon, AZ · 26 mi

857559a

Tucson, AZ · 27 mi

Arizona planting zones →

Questions about 85618

What planting zone is ZIP code 85618?

ZIP code 85618 (Mammoth, 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).

When is the last frost in Mammoth, AZ?

The median last spring frost (32 °F) near 85618 is March 29; after April 29 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Oracle Sp station.

When is the first frost in Mammoth, AZ?

The median first fall frost near 85618 is November 13, giving a median frost-free growing season of 225 days.

When should I plant tomatoes in 85618?

Start tomato seeds indoors around Feb 1 – Feb 15 and set transplants outside around Apr 5 – Apr 19, one to three weeks after the median last frost.

How much rain and snow does 85618 get?

About 15.6 inches of precipitation a year (NOAA 1991–2020 normals, Oracle Sp station).

How hot do summers get in Mammoth, AZ?

The average high peaks at 94 °F in June, with about 94 days a year at 90 °F or more.

What kind of soil does 85618 have?

The USDA soil survey maps Stagecoach at the center of ZIP 85618: extremely cobbly sandy loam, somewhat excessively drained, pH about 7.6 (slightly alkaline).

Did spring come early in Mammoth, AZ in 2026?

Spring leaf-out near 85618 came on Jan 27 in 2026, about the same as the 1991–2020 average (Jan 28), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Mammoth, AZ?

Intermediate onions: the longest day near 85618 is 14 h 19 min, so day-neutral types bulb best; long-day varieties may not bulb fully.