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

Planting zone for 78240 — San Antonio, TX

ZIP code 78240 (San Antonio, Bexar County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F. The median last spring frost is February 26 and the first fall frost November 28.

Where ZIP 78240 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 26
First frostNov 28
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 San Antonio, 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 San Antonio, TX

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostFebruary 26median — 50% chance of a later frost
Safe for tender plantsMarch 17only 10% chance of frost after
First fall frostNovember 28median — 10% chance by Nov 7
Growing season277 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 9 and returns around December 13.

From the NOAA station San Antonio Intl Airport, TX — 7 miles away, elevation 791 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 78240

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Jan 15 – Jan 29
SpinachSow outdoors · Jan 15 – Feb 5
Broccoli, cabbageStart indoors · Dec 18 – Jan 1
Broccoli, cabbageTransplant · Feb 5 – Feb 19
Onion setsPlant outdoors · Jan 29 – Feb 12
PotatoesPlant outdoors · Feb 5 – Feb 19
LettuceSow outdoors · Jan 29 – Feb 12
Carrots, beetsSow outdoors · Feb 5 – Feb 19
TomatoesStart indoors · Jan 1 – Jan 15
TomatoesTransplant · Mar 5 – Mar 19
Peppers, eggplantStart indoors · Dec 18 – Jan 1
Peppers, eggplantTransplant · Mar 12 – Mar 26
BeansSow outdoors · Mar 5 – Mar 19
Sweet cornSow outdoors · Mar 5 – Mar 19
Cucumbers, squashSow outdoors · Mar 5 – Mar 19
Fall lettuce, spinachSow outdoors · Oct 3 – Oct 17
GarlicPlant cloves · Nov 14 – Dec 19
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Feb 26) and first fall frost (Nov 28) 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 78240 came on Jan 20 — 5 days earlier than the 1991–2020 average (Jan 25).

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).

Soil in San Antonio, TX

The soil mapped at the center of ZIP 78240 is Whitewright — clay loam, well drained.

TextureClay loamholds water and nutrients; slow to drain and warm up
pH8.2alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter0.75%low — add compost
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Whitewright-Austin complex, 1 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 78240; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in San Antonio, TX

Summer high96 °Faverage high, August
Winter low41 °Faverage low, January
Hot days122days a year at 90 °F or more
Freezing nights14nights a year at 32 °F or less
Growing degree days7,392base 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
Precipitation36.6 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°110°32 °FJanuary: average high 63 °F, low 41 °F 63°41° JanFebruary: average high 68 °F, low 45 °F 68°45° FebMarch: average high 74 °F, low 52 °F 74°52° MarApril: average high 80 °F, low 58 °F 80°58° AprMay: average high 87 °F, low 66 °F 87°66° MayJune: average high 92 °F, low 73 °F 92°73° JunJuly: average high 95 °F, low 75 °F 95°75° JulAugust: average high 96 °F, low 75 °F 96°75° AugSeptember: average high 90 °F, low 70 °F 90°70° SepOctober: average high 82 °F, low 60 °F 82°60° OctNovember: average high 72 °F, low 50 °F 72°50° NovDecember: average high 65 °F, low 42 °F 65°42° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 2.11 in precipitation 2.1 JanFebruary: 1.91 in precipitation 1.9 FebMarch: 2.59 in precipitation 2.6 MarApril: 2.46 in precipitation 2.5 AprMay: 4.96 in precipitation 5.0 MayJune: 3.57 in precipitation 3.6 JunJuly: 3.04 in precipitation 3.0 JulAugust: 2.82 in precipitation 2.8 AugSeptember: 4.17 in precipitation 4.2 SepOctober: 4.14 in precipitation 4.1 OctNovember: 2.80 in precipitation 2.8 NovDecember: 2.07 in precipitation 2.1 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: San Antonio Intl Airport, TX (7 mi away); precipitation: Leon Valley 1.6 N, TX (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 9a.

782299a
San Antonio, TX · 2 mi
782499a
San Antonio, TX · 3 mi
782309a
San Antonio, TX · 3 mi
782389a
San Antonio, TX · 4 mi
782509a
San Antonio, TX · 4 mi
782289a
San Antonio, TX · 5 mi
782139a
San Antonio, TX · 5 mi
782319a
San Antonio, TX · 5 mi

All 82 ZIP codes in San Antonio → · Texas planting zones →

Questions about 78240

What planting zone is ZIP code 78240?

ZIP code 78240 (San Antonio, 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 San Antonio, TX?

The median last spring frost (32 °F) near 78240 is February 26; after March 17 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, San Antonio Intl Airport station.

When is the first frost in San Antonio, TX?

The median first fall frost near 78240 is November 28, giving a median frost-free growing season of 277 days.

When should I plant tomatoes in 78240?

Start tomato seeds indoors around Jan 1 – Jan 15 and set transplants outside around Mar 5 – Mar 19, one to three weeks after the median last frost.

How much rain and snow does 78240 get?

About 36.6 inches of precipitation a year (NOAA 1991–2020 normals, Leon Valley 1.6 N station).

How hot do summers get in San Antonio, TX?

The average high peaks at 96 °F in August, with about 122 days a year at 90 °F or more.

What kind of soil does 78240 have?

The USDA soil survey maps Whitewright at the center of ZIP 78240: clay loam, well drained, pH about 8.2 (alkaline).

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

Spring leaf-out near 78240 came on Jan 20 in 2026, 5 days earlier than the 1991–2020 average (Jan 25), according to the USA National Phenology Network Spring Index.

What kind of onions grow in San Antonio, TX?

Short-day onions: the longest day near 78240 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 78240 change?

Yes. The 2012 USDA map put 78240 in zone 8b; the 2023 map puts it in zone 9a. The newer map uses 1991–2020 data and more weather stations.