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

Planting zone for 78066 — Rio Medina, TX

ZIP code 78066 (Rio Medina, Medina County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F. The median last spring frost is February 18 and the first fall frost December 9.

Where ZIP 78066 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 frostFeb 18

First frostDec 9

2012 zone8b

Was 8b 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 9a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Rio Medina, TX…

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 Medina, TX

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostFebruary 18median — 50% chance of a later frost

Safe for tender plantsMarch 16only 10% chance of frost after

First fall frostDecember 9median — 10% chance by Nov 17

Growing season296 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 31 and returns around December 29.

From the NOAA station San Antonio/Seaworld, TX — 12 miles away, elevation 942 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 78066

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Jan 7 – Jan 21

SpinachSow outdoors · Jan 7 – Jan 28

Broccoli, cabbageStart indoors · Dec 10 – Dec 24

Broccoli, cabbageTransplant · Jan 28 – Feb 11

Onion setsPlant outdoors · Jan 21 – Feb 4

PotatoesPlant outdoors · Jan 28 – Feb 11

LettuceSow outdoors · Jan 21 – Feb 4

Carrots, beetsSow outdoors · Jan 28 – Feb 11

TomatoesStart indoors · Dec 24 – Jan 7

TomatoesTransplant · Feb 25 – Mar 11

Peppers, eggplantStart indoors · Dec 10 – Dec 24

Peppers, eggplantTransplant · Mar 4 – Mar 18

BeansSow outdoors · Feb 25 – Mar 11

Sweet cornSow outdoors · Feb 25 – Mar 11

Cucumbers, squashSow outdoors · Feb 25 – Mar 11

Fall lettuce, spinachSow outdoors · Oct 14 – Oct 28

GarlicPlant cloves · Nov 25 – Dec 30

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Feb 18) and first fall frost (Dec 9) 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 78066 came on Jan 29 — 4 days later than the 1991–2020 average (Jan 25).

average
Jan 252026
Jan 29

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 Texas

640 plants native to the lower 48 states, recorded in Texas, 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 Rio Medina, TX.

Soil in Rio Medina, TX

The soil mapped at the center of ZIP 78066 is Knippa — clay, well drained.

TextureClayholds water and nutrients; slow to drain and warm up

pH7.8slightly alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2.2%moderate

Hydrologic groupCwater soaks in slowly

Farmland classprime farmlandUSDA classification

Map unit: Knippa clay, 0 to 1 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 78066; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Rio Medina, TX

Summer high99 °Faverage high, August

Winter low43 °Faverage low, January

Hot days123days a year at 90 °F or more

Freezing nights14nights a year at 32 °F or less

Growing degree days7,892base 50 °F — the season’s usable heat

Longest day14 h 02 mindaylight on June 21

Shortest day10 h 15 mindaylight on December 21

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

Precipitation30.9 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: San Antonio/Seaworld, TX (12 mi away); precipitation: Riomedina, TX (4 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.

780569a

Mico, TX · 4 mi

782539a

San Antonio, TX · 6 mi

780099a

Castroville, TX · 9 mi

782549a

San Antonio, TX · 10 mi

782459a

San Antonio, TX · 11 mi

San Antonio, TX · 13 mi

Texas planting zones →

Questions about 78066

What planting zone is ZIP code 78066?

ZIP code 78066 (Rio Medina, TX) 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 Rio Medina, TX?

The median last spring frost (32 °F) near 78066 is February 18; after March 16 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, San Antonio/Seaworld station.

When is the first frost in Rio Medina, TX?

The median first fall frost near 78066 is December 9, giving a median frost-free growing season of 296 days.

When should I plant tomatoes in 78066?

Start tomato seeds indoors around Dec 24 – Jan 7 and set transplants outside around Feb 25 – Mar 11, one to three weeks after the median last frost.

How much rain and snow does 78066 get?

About 30.9 inches of precipitation a year (NOAA 1991–2020 normals, Riomedina station).

How hot do summers get in Rio Medina, TX?

The average high peaks at 99 °F in August, with about 123 days a year at 90 °F or more.

What kind of soil does 78066 have?

The USDA soil survey maps Knippa at the center of ZIP 78066: clay, well drained, pH about 7.8 (slightly alkaline).

Did spring come early in Rio Medina, TX in 2026?

Spring leaf-out near 78066 came on Jan 29 in 2026, 4 days later than the 1991–2020 average (Jan 25), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Rio Medina, TX?

Short-day onions: the longest day near 78066 is 14 h 02 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.

Did the zone for 78066 change?

Yes. The 2012 USDA map put 78066 in zone 8b; the 2023 map puts it in zone 9a. The newer map uses 1991–2020 data and more weather stations.