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

Planting zone for 78338 — Armstrong, TX

ZIP code 78338 (Armstrong, Kenedy County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F. The median last spring frost is February 22 and the first fall frost December 5.

Where ZIP 78338 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.

Zone9b25 to 30 °F

Coldest night−3.9 to −1.1 °C

Last frostFeb 22

First frostDec 5

2012 zone9b

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 9b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Armstrong, 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 Armstrong, TX

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostFebruary 22median — 50% chance of a later frost

Safe for tender plantsMarch 14only 10% chance of frost after

First fall frostDecember 5median — 10% chance by Nov 15

Growing season293 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 31 and returns around December 22.

From the NOAA station Armstrong 4se, TX — 2 miles away, elevation 26 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 78338

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Jan 11 – Jan 25

SpinachSow outdoors · Jan 11 – Feb 1

Broccoli, cabbageStart indoors · Dec 14 – Dec 28

Broccoli, cabbageTransplant · Feb 1 – Feb 15

Onion setsPlant outdoors · Jan 25 – Feb 8

PotatoesPlant outdoors · Feb 1 – Feb 15

LettuceSow outdoors · Jan 25 – Feb 8

Carrots, beetsSow outdoors · Feb 1 – Feb 15

TomatoesStart indoors · Dec 28 – Jan 11

TomatoesTransplant · Mar 1 – Mar 15

Peppers, eggplantStart indoors · Dec 14 – Dec 28

Peppers, eggplantTransplant · Mar 8 – Mar 22

BeansSow outdoors · Mar 1 – Mar 15

Sweet cornSow outdoors · Mar 1 – Mar 15

Cucumbers, squashSow outdoors · Mar 1 – Mar 15

Fall lettuce, spinachSow outdoors · Oct 10 – Oct 24

GarlicPlant cloves · Nov 21 – Dec 26

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Feb 22) and first fall frost (Dec 5) 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 78338 came on Jan 10 — 8 days earlier than the 1991–2020 average (Jan 18).

average
Jan 182026
Jan 10

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 9b in Texas

646 plants native to the lower 48 states, recorded in Texas, and rated by the USDA to survive 25 °F or colder — the bottom of zone 9b. 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 Armstrong, TX.

Soil in Armstrong, TX

The soil mapped at the center of ZIP 78338 is Falfurrias — fine sand, excessively drained.

TextureFine sanddrains and warms fast; dries out and needs more feeding

pH6.4slightly acidic; most vegetables like 6.0–7.0

DrainageExcessively drainednatural drainage class

Organic matter0.38%low — add compost

Hydrologic groupAwater soaks in fast

Farmland classNot prime farmlandUSDA classification

Map unit: Falfurrias fine sand, 5 to 15 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 78338; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Armstrong, TX

Summer high98 °Faverage high, August

Winter low45 °Faverage low, January

Hot days169days a year at 90 °F or more

Freezing nights11nights a year at 32 °F or less

Growing degree days8,573base 50 °F — the season’s usable heat

Longest day13 h 50 mindaylight on June 21

Shortest day10 h 27 mindaylight on December 21

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

Precipitation28.1 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: Armstrong 4se, TX (2 mi away); precipitation: Armstrong 4se, TX (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

783859b

Sarita, TX · 19 mi

7858010a

Raymondville, TX · 25 mi

7859010a

San Perlita, TX · 25 mi

785409b

Edinburg, TX · 27 mi

7859810a

Port Mansfield, TX · 29 mi

Texas planting zones →

Questions about 78338

What planting zone is ZIP code 78338?

ZIP code 78338 (Armstrong, TX) is in USDA hardiness zone 9b on the 2023 map: the coldest night of an average winter reaches 25 to 30 °F (−3.9 to −1.1 °C).

When is the last frost in Armstrong, TX?

The median last spring frost (32 °F) near 78338 is February 22; after March 14 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Armstrong 4se station.

When is the first frost in Armstrong, TX?

The median first fall frost near 78338 is December 5, giving a median frost-free growing season of 293 days.

When should I plant tomatoes in 78338?

Start tomato seeds indoors around Dec 28 – Jan 11 and set transplants outside around Mar 1 – Mar 15, one to three weeks after the median last frost.

How much rain and snow does 78338 get?

About 28.1 inches of precipitation a year (NOAA 1991–2020 normals, Armstrong 4se station).

How hot do summers get in Armstrong, TX?

The average high peaks at 98 °F in August, with about 169 days a year at 90 °F or more.

What kind of soil does 78338 have?

The USDA soil survey maps Falfurrias at the center of ZIP 78338: fine sand, excessively drained, pH about 6.4 (slightly acidic).

Did spring come early in Armstrong, TX in 2026?

Spring leaf-out near 78338 came on Jan 10 in 2026, 8 days earlier than the 1991–2020 average (Jan 18), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Armstrong, TX?

Short-day onions: the longest day near 78338 is 13 h 50 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.