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

Planting zone for 78731 — Austin, TX

ZIP code 78731 (Austin, Travis County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F. The median last spring frost is February 20 and the first fall frost December 3.

Where ZIP 78731 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 20

First frostDec 3

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 Austin, 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 Austin, TX

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostFebruary 20median — 50% chance of a later frost

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

First fall frostDecember 3median — 10% chance by Nov 15

Growing season291 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 1 and returns around December 27.

From the NOAA station Austin-Camp Mabry, TX — 2 miles away, elevation 669 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 78731

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Jan 9 – Jan 23

SpinachSow outdoors · Jan 9 – Jan 30

Broccoli, cabbageStart indoors · Dec 12 – Dec 26

Broccoli, cabbageTransplant · Jan 30 – Feb 13

Onion setsPlant outdoors · Jan 23 – Feb 6

PotatoesPlant outdoors · Jan 30 – Feb 13

LettuceSow outdoors · Jan 23 – Feb 6

Carrots, beetsSow outdoors · Jan 30 – Feb 13

TomatoesStart indoors · Dec 26 – Jan 9

TomatoesTransplant · Feb 27 – Mar 13

Peppers, eggplantStart indoors · Dec 12 – Dec 26

Peppers, eggplantTransplant · Mar 6 – Mar 20

BeansSow outdoors · Feb 27 – Mar 13

Sweet cornSow outdoors · Feb 27 – Mar 13

Cucumbers, squashSow outdoors · Feb 27 – Mar 13

Fall lettuce, spinachSow outdoors · Oct 8 – Oct 22

GarlicPlant cloves · Nov 19 – Dec 24

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Feb 20) and first fall frost (Dec 3) 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 78731 came on Jan 29 — about the same time as the 1991–2020 average (Jan 27).

average
Jan 272026
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).

Soil in Austin, TX

The soil mapped at the center of ZIP 78731 is Brackett — gravelly clay loam, well drained. Much of the area is built over (urban land); this is the natural soil underneath.

TextureGravelly clay loamholds water and nutrients; slow to drain and warm up

pH7.9alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2%moderate

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Urban land and Brackett soils, 1 to 12 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 78731; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Austin, TX

Summer high98 °Faverage high, August

Winter low42 °Faverage low, January

Hot days123days a year at 90 °F or more

Freezing nights12nights a year at 32 °F or less

Growing degree days7,547base 50 °F — the season’s usable heat

Longest day14 h 06 mindaylight on June 21

Shortest day10 h 11 mindaylight on December 21

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

Precipitation36.3 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: Austin-Camp Mabry, TX (2 mi away); precipitation: Austin-Camp Mabry, TX (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 9a.

All 73 ZIP codes in Austin → · Texas planting zones →

Questions about 78731

What planting zone is ZIP code 78731?

ZIP code 78731 (Austin, 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 Austin, TX?

The median last spring frost (32 °F) near 78731 is February 20; after March 14 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Austin-Camp Mabry station.

When is the first frost in Austin, TX?

The median first fall frost near 78731 is December 3, giving a median frost-free growing season of 291 days.

When should I plant tomatoes in 78731?

Start tomato seeds indoors around Dec 26 – Jan 9 and set transplants outside around Feb 27 – Mar 13, one to three weeks after the median last frost.

How much rain and snow does 78731 get?

About 36.3 inches of precipitation a year (NOAA 1991–2020 normals, Austin-Camp Mabry station).

How hot do summers get in Austin, TX?

The average high peaks at 98 °F in August, with about 123 days a year at 90 °F or more.

What kind of soil does 78731 have?

The USDA soil survey maps Brackett at the center of ZIP 78731: gravelly clay loam, well drained, pH about 7.9 (alkaline).

Did spring come early in Austin, TX in 2026?

Spring leaf-out near 78731 came on Jan 29 in 2026, about the same as the 1991–2020 average (Jan 27), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Austin, TX?

Short-day onions: the longest day near 78731 is 14 h 06 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.

Did the zone for 78731 change?

Yes. The 2012 USDA map put 78731 in zone 8b; the 2023 map puts it in zone 9a. The newer map uses 1991–2020 data and more weather stations.