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

Planting zone for 85638 — Tombstone, AZ

ZIP code 85638 (Tombstone, Cochise County) is in USDA zone 8b: the coldest winter night averages 15 to 20 °F. The median last spring frost is March 4 and the first fall frost November 29.

Where ZIP 85638 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.

Zone8b15 to 20 °F

Coldest night−9.4 to −6.7 °C

Last frostMar 4

First frostNov 29

2012 zone9a

Was 9a 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 8b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Tombstone, 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 Tombstone, AZ

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMarch 4median — 50% chance of a later frost

Safe for tender plantsMarch 31only 10% chance of frost after

First fall frostNovember 29median — 10% chance by Nov 12

Growing season264 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 8 and returns around December 12.

From the NOAA station Tombstone, AZ — 3 miles away, elevation 4,659 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 85638

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Jan 21 – Feb 4

SpinachSow outdoors · Jan 21 – Feb 11

Broccoli, cabbageStart indoors · Dec 24 – Jan 7

Broccoli, cabbageTransplant · Feb 11 – Feb 25

Onion setsPlant outdoors · Feb 4 – Feb 18

PotatoesPlant outdoors · Feb 11 – Feb 25

LettuceSow outdoors · Feb 4 – Feb 18

Carrots, beetsSow outdoors · Feb 11 – Feb 25

TomatoesStart indoors · Jan 7 – Jan 21

TomatoesTransplant · Mar 11 – Mar 25

Peppers, eggplantStart indoors · Dec 24 – Jan 7

Peppers, eggplantTransplant · Mar 18 – Apr 1

BeansSow outdoors · Mar 11 – Mar 25

Sweet cornSow outdoors · Mar 11 – Mar 25

Cucumbers, squashSow outdoors · Mar 11 – Mar 25

Fall lettuce, spinachSow outdoors · Oct 4 – Oct 18

GarlicPlant cloves · Nov 15 – Dec 20

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 4) and first fall frost (Nov 29) 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 85638 came on Jan 31 — about the same time as the 1991–2020 average (Jan 30).

average
Jan 302026
Jan 31

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 8b in Arizona

482 plants native to the lower 48 states, recorded in Arizona, and rated by the USDA to survive 15 °F or colder — the bottom of zone 8b. 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 Tombstone, AZ.

Soil in Tombstone, AZ

The soil mapped at the center of ZIP 85638 is Mabray — extremely cobbly loam, well drained.

TextureExtremely cobbly loama good balance for most vegetables

pH7.9alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter1.5%low — add compost

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Mabray-Rock outcrop complex, 3 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 85638; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Tombstone, AZ

Summer high96 °Faverage high, June

Winter low38 °Faverage low, January

Hot days101days a year at 90 °F or more

Freezing nights29nights a year at 32 °F or less

Growing degree days6,036base 50 °F — the season’s usable heat

Longest day14 h 13 mindaylight on June 21

Shortest day10 h 05 mindaylight on December 21

Onions to growShort-daysummer days stay under about 14 h 20 min, so long-day varieties won’t bulb

Precipitation13.2 inper year, rain and melted snow

Snowfall1 inper year; 1 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Tombstone, AZ (3 mi away); precipitation: Tombstone, AZ (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 8b.

856358b

Sierra Vista, AZ · 10 mi

856368b

Sierra Vista, AZ · 13 mi

856508b

Sierra Vista, AZ · 14 mi

856168b

Huachuca City, AZ · 16 mi

856718b

Sierra Vista, AZ · 16 mi

856308b

Saint David, AZ · 17 mi

Arizona planting zones →

Questions about 85638

What planting zone is ZIP code 85638?

ZIP code 85638 (Tombstone, AZ) is in USDA hardiness zone 8b on the 2023 map: the coldest night of an average winter reaches 15 to 20 °F (−9.4 to −6.7 °C).

When is the last frost in Tombstone, AZ?

The median last spring frost (32 °F) near 85638 is March 4; after March 31 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Tombstone station.

When is the first frost in Tombstone, AZ?

The median first fall frost near 85638 is November 29, giving a median frost-free growing season of 264 days.

When should I plant tomatoes in 85638?

Start tomato seeds indoors around Jan 7 – Jan 21 and set transplants outside around Mar 11 – Mar 25, one to three weeks after the median last frost.

How much rain and snow does 85638 get?

About 13.2 inches of precipitation a year and 1 inches of snowfall (NOAA 1991–2020 normals, Tombstone station).

How hot do summers get in Tombstone, AZ?

The average high peaks at 96 °F in June, with about 101 days a year at 90 °F or more.

What kind of soil does 85638 have?

The USDA soil survey maps Mabray at the center of ZIP 85638: extremely cobbly loam, well drained, pH about 7.9 (alkaline).

Did spring come early in Tombstone, AZ in 2026?

Spring leaf-out near 85638 came on Jan 31 in 2026, about the same as the 1991–2020 average (Jan 30), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Tombstone, AZ?

Short-day onions: the longest day near 85638 is 14 h 13 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.

Did the zone for 85638 change?

Yes. The 2012 USDA map put 85638 in zone 9a; the 2023 map puts it in zone 8b. The newer map uses 1991–2020 data and more weather stations.