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

Planting zone for 85648 — Rio Rico, AZ

ZIP code 85648 (Rio Rico, Santa Cruz County) is in USDA zone 8b: the coldest winter night averages 15 to 20 °F. The median last spring frost is April 16 and the first fall frost November 2.

Where ZIP 85648 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 frostApr 16

First frostNov 2

2012 zone8a

Was 8a on the 2012 map — half a zone warmer 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 Rio Rico, 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 Rio Rico, AZ

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 16median — 50% chance of a later frost

Safe for tender plantsMay 4only 10% chance of frost after

First fall frostNovember 2median — 10% chance by Oct 19

Growing season199 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 22 and returns around November 14.

From the NOAA station Nogales 6 N, AZ — 4 miles away, elevation 3,461 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 85648

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 5 – Mar 19

SpinachSow outdoors · Mar 5 – Mar 26

Broccoli, cabbageStart indoors · Feb 5 – Feb 19

Broccoli, cabbageTransplant · Mar 26 – Apr 9

Onion setsPlant outdoors · Mar 19 – Apr 2

PotatoesPlant outdoors · Mar 26 – Apr 9

LettuceSow outdoors · Mar 19 – Apr 2

Carrots, beetsSow outdoors · Mar 26 – Apr 9

TomatoesStart indoors · Feb 19 – Mar 5

TomatoesTransplant · Apr 23 – May 7

Peppers, eggplantStart indoors · Feb 5 – Feb 19

Peppers, eggplantTransplant · Apr 30 – May 14

BeansSow outdoors · Apr 23 – May 7

Sweet cornSow outdoors · Apr 23 – May 7

Cucumbers, squashSow outdoors · Apr 23 – May 7

Fall lettuce, spinachSow outdoors · Sep 7 – Sep 21

GarlicPlant cloves · Oct 19 – Nov 23

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 16) and first fall frost (Nov 2) 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 85648 came on Jan 26 — 4 days earlier than the 1991–2020 average (Jan 30).

average
Jan 302026
Jan 26

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 Rio Rico, AZ.

Soil in Rio Rico, AZ

The soil mapped at the center of ZIP 85648 is Grabe — sandy loam, well drained.

TextureSandy loamdrains and warms fast; dries out and needs more feeding

pH7.9alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter1%low — add compost

Hydrologic groupAwater soaks in fast

Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Grabe-Comoro complex, 0 to 5 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 85648; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Rio Rico, AZ

Summer high97 °Faverage high, June

Winter low28 °Faverage low, January

Hot days118days a year at 90 °F or more

Freezing nights92nights a year at 32 °F or less

Growing degree days4,976base 50 °F — the season’s usable heat

Longest day14 h 12 mindaylight on June 21

Shortest day10 h 06 mindaylight on December 21

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

Precipitation16.1 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: Nogales 6 N, AZ (4 mi away); precipitation: Nogales 6 N, AZ (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

856408b

Tumacacori, AZ · 6 mi

Patagonia, AZ · 16 mi

856018b

Arivaca, AZ · 20 mi

856229a

Green Valley, AZ · 22 mi

Arizona planting zones →

Questions about 85648

What planting zone is ZIP code 85648?

ZIP code 85648 (Rio Rico, 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 Rio Rico, AZ?

The median last spring frost (32 °F) near 85648 is April 16; after May 4 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Nogales 6 N station.

When is the first frost in Rio Rico, AZ?

The median first fall frost near 85648 is November 2, giving a median frost-free growing season of 199 days.

When should I plant tomatoes in 85648?

Start tomato seeds indoors around Feb 19 – Mar 5 and set transplants outside around Apr 23 – May 7, one to three weeks after the median last frost.

How much rain and snow does 85648 get?

About 16.1 inches of precipitation a year (NOAA 1991–2020 normals, Nogales 6 N station).

How hot do summers get in Rio Rico, AZ?

The average high peaks at 97 °F in June, with about 118 days a year at 90 °F or more.

What kind of soil does 85648 have?

The USDA soil survey maps Grabe at the center of ZIP 85648: sandy loam, well drained, pH about 7.9 (alkaline).

Did spring come early in Rio Rico, AZ in 2026?

Spring leaf-out near 85648 came on Jan 26 in 2026, 4 days earlier than the 1991–2020 average (Jan 30), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Rio Rico, AZ?

Short-day onions: the longest day near 85648 is 14 h 12 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.

Did the zone for 85648 change?

Yes. The 2012 USDA map put 85648 in zone 8a; the 2023 map puts it in zone 8b. The newer map uses 1991–2020 data and more weather stations.