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

Planting zone for 78551 — Harlingen, TX

ZIP code 78551 (Harlingen, Cameron County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F.

Where ZIP 78551 is

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.

Zone10a30 to 35 °F
Coldest night−1.1 to 1.7 °C
Last frostrare
First frostrare
2012 zone9b

Was 9b 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 10a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Harlingen, 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

A 32 °F frost doesn't happen here in most winters. At the nearest station (NOAA station Harlingen, TX — 4 miles away, elevation 39 ft) the median growing season is 365 days. When frost does come, it is a midwinter night or two; cover tender plants when a freeze is forecast.

Frost data: NOAA NCEI U.S. Climate Normals 1991–2020.

When spring arrived in 2026

In 2026, spring leaf-out near 78551 came on Jan 9 — 7 days earlier than the 1991–2020 average (Jan 16).

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 10a in Texas

651 plants native to the lower 48 states, recorded in Texas, and rated by the USDA to survive 30 °F or colder — the bottom of zone 10a. Each links to its USDA PLANTS profile.

Trees 72

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °FArizona cypress50 ft · blooms spring · low shade tolerance · to −23 °FArizona walnut50 ft · blooms late spring · high shade tolerance · to −33 °F

Shrubs 147

alderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °Faloe yucca15 ft · blooms early summer · medium shade tolerance · to −1 °FAmerican beautyberry6 ft · blooms early summer · medium shade tolerance · to −8 °FAmerican holly40 ft · blooms mid spring · low shade tolerance · to −20 °FAmerican hornbeam30 ft · blooms mid spring · low shade tolerance · to −34 °FAmerican snowbell10 ft · blooms spring · medium shade tolerance · to −16 °F

Wildflowers & perennials 212

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican century plant6 ft · blooms indeterminate · high shade tolerance · to 12 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °F

Grasses 197

alkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °FAmerican cupscale3 ft · blooms early summer · high shade tolerance · to −18 °FArizona cottontop4 ft · blooms late summer · high shade tolerance · to −13 °FArizona fescue2 ft · blooms late spring · high shade tolerance · to −23 °FArizona threeawn2 ft · blooms mid summer · high shade tolerance · to −3 °Fautumn bluegrass1.5 ft · blooms late spring · medium shade tolerance · to −8 °F

Vines 14

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °FAmerican wisteria50 ft · blooms spring · low shade tolerance · to −3 °Fcatbird grape30 ft · blooms late spring · medium shade tolerance · to −13 °Fcupseed30 ft · blooms late spring · low shade tolerance · to −3 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °F

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 Harlingen, TX.

Soil in Harlingen, TX

The soil mapped at the center of ZIP 78551 is Racombes — sandy clay loam, well drained.

TextureSandy clay loamholds water and nutrients; slow to drain and warm up
pH7.5slightly alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2%moderate
Hydrologic groupBwater soaks in moderately
Farmland classprime farmlandUSDA classification

Map unit: Racombes sandy clay loam, 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 78551; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Harlingen, TX

Summer high98 °Faverage high, August
Winter low51 °Faverage low, January
Hot days151days a year at 90 °F or more
Freezing nights1nights a year at 32 °F or less
Growing degree days9,413base 50 °F — the season’s usable heat
Longest day13 h 47 mindaylight on June 21
Shortest day10 h 30 mindaylight on December 21
Onions to growShort-daysummer days stay under about 14 h 20 min, so long-day varieties won’t bulb
Precipitation26.6 inper year, rain and melted snow

Average high and low, by month

40°50°60°70°80°90°100°110°January: average high 72 °F, low 51 °F 72°51° JanFebruary: average high 76 °F, low 55 °F 76°55° FebMarch: average high 81 °F, low 60 °F 81°60° MarApril: average high 86 °F, low 66 °F 86°66° AprMay: average high 91 °F, low 72 °F 91°72° MayJune: average high 95 °F, low 76 °F 95°76° JunJuly: average high 97 °F, low 77 °F 97°77° JulAugust: average high 98 °F, low 77 °F 98°77° AugSeptember: average high 93 °F, low 74 °F 93°74° SepOctober: average high 88 °F, low 67 °F 88°67° OctNovember: average high 80 °F, low 59 °F 80°59° NovDecember: average high 73 °F, low 53 °F 73°53° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 1.18 in precipitation 1.2 JanFebruary: 1.13 in precipitation 1.1 FebMarch: 1.41 in precipitation 1.4 MarApril: 1.53 in precipitation 1.5 AprMay: 1.96 in precipitation 2.0 MayJune: 3.29 in precipitation 3.3 JunJuly: 3.91 in precipitation 3.9 JulAugust: 1.46 in precipitation 1.5 AugSeptember: 5.11 in precipitation 5.1 SepOctober: 2.60 in precipitation 2.6 OctNovember: 1.72 in precipitation 1.7 NovDecember: 1.27 in precipitation 1.3 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Harlingen, TX (4 mi away); precipitation: Harlingen 0.4 N, TX (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 10a.

7853510a
Combes, TX · <1 mi
7855010a
Harlingen, TX · 4 mi
7855210a
Harlingen, TX · 4 mi
7855310a
Harlingen, TX · 4 mi
7859310a
Santa Rosa, TX · 7 mi
7859410a
Sebastian, TX · 9 mi
7856910a
Lyford, TX · 9 mi
7855910a
La Feria, TX · 9 mi

All 4 ZIP codes in Harlingen → · Texas planting zones →

Questions about 78551

What planting zone is ZIP code 78551?

ZIP code 78551 (Harlingen, TX) is in USDA hardiness zone 10a on the 2023 map: the coldest night of an average winter reaches 30 to 35 °F (−1.1 to 1.7 °C).

How much rain and snow does 78551 get?

About 26.6 inches of precipitation a year (NOAA 1991–2020 normals, Harlingen 0.4 N station).

How hot do summers get in Harlingen, TX?

The average high peaks at 98 °F in August, with about 151 days a year at 90 °F or more.

What kind of soil does 78551 have?

The USDA soil survey maps Racombes at the center of ZIP 78551: sandy clay loam, well drained, pH about 7.5 (slightly alkaline).

Did spring come early in Harlingen, TX in 2026?

Spring leaf-out near 78551 came on Jan 9 in 2026, 7 days earlier than the 1991–2020 average (Jan 16), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Harlingen, TX?

Short-day onions: the longest day near 78551 is 13 h 47 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.

Did the zone for 78551 change?

Yes. The 2012 USDA map put 78551 in zone 9b; the 2023 map puts it in zone 10a. The newer map uses 1991–2020 data and more weather stations.