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

Planting zone for 78588 — San Isidro, TX

ZIP code 78588 (San Isidro, Starr County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F.

Where ZIP 78588 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 frostrare

First frostrare

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 San Isidro, 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 Mccook, TX — 21 miles away, elevation 220 ft) the median growing season is 333 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 78588 came on Jan 10 — 7 days earlier than the 1991–2020 average (Jan 17).

average
Jan 172026
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 San Isidro, TX.

Soil in San Isidro, TX

The soil mapped at the center of ZIP 78588 is Sarita — fine sand, well drained.

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

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

DrainageWell drainednatural drainage class

Organic matter0.45%low — add compost

Hydrologic groupAwater soaks in fast

Farmland classNot prime farmlandUSDA classification

Map unit: Sarita fine sand, 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 78588; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in San Isidro, TX

Summer high98 °Faverage high, August

Winter low47 °Faverage low, January

Hot days170days a year at 90 °F or more

Freezing nights3nights a year at 32 °F or less

Growing degree days8,634base 50 °F — the season’s usable heat

Longest day13 h 49 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

Precipitation24.3 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: Mccook, TX (21 mi away); precipitation: Rio Grande City 17.7 Ne, TX (19 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.

Santa Elena, TX · 12 mi

Rio Grande City, TX · 26 mi

Texas planting zones →

Questions about 78588

What planting zone is ZIP code 78588?

ZIP code 78588 (San Isidro, 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).

How much rain and snow does 78588 get?

About 24.3 inches of precipitation a year (NOAA 1991–2020 normals, Rio Grande City 17.7 Ne station).

How hot do summers get in San Isidro, TX?

The average high peaks at 98 °F in August, with about 170 days a year at 90 °F or more.

What kind of soil does 78588 have?

The USDA soil survey maps Sarita at the center of ZIP 78588: fine sand, well drained, pH about 6.4 (slightly acidic).

Did spring come early in San Isidro, TX in 2026?

Spring leaf-out near 78588 came on Jan 10 in 2026, 7 days earlier than the 1991–2020 average (Jan 17), according to the USA National Phenology Network Spring Index.

What kind of onions grow in San Isidro, TX?

Short-day onions: the longest day near 78588 is 13 h 49 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.