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

Planting zone for 78680 — Round Rock, TX

ZIP code 78680 (Round Rock, Williamson County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F. The median last spring frost is March 6 and the first fall frost November 24.

Where ZIP 78680 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.

Zone9a20 to 25 °F
Coldest night−6.7 to −3.9 °C
Last frostMar 6
First frostNov 24
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 Round Rock, 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 Round Rock, TX

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMarch 6median — 50% chance of a later frost
Safe for tender plantsMarch 30only 10% chance of frost after
First fall frostNovember 24median — 10% chance by Nov 5
Growing season259 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 23 and returns around December 5.

From the NOAA station Georgetown Lake, TX — 7 miles away, elevation 873 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 78680

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Jan 23 – Feb 6
SpinachSow outdoors · Jan 23 – Feb 13
Broccoli, cabbageStart indoors · Dec 26 – Jan 9
Broccoli, cabbageTransplant · Feb 13 – Feb 27
Onion setsPlant outdoors · Feb 6 – Feb 20
PotatoesPlant outdoors · Feb 13 – Feb 27
LettuceSow outdoors · Feb 6 – Feb 20
Carrots, beetsSow outdoors · Feb 13 – Feb 27
TomatoesStart indoors · Jan 9 – Jan 23
TomatoesTransplant · Mar 13 – Mar 27
Peppers, eggplantStart indoors · Dec 26 – Jan 9
Peppers, eggplantTransplant · Mar 20 – Apr 3
BeansSow outdoors · Mar 13 – Mar 27
Sweet cornSow outdoors · Mar 13 – Mar 27
Cucumbers, squashSow outdoors · Mar 13 – Mar 27
Fall lettuce, spinachSow outdoors · Sep 29 – Oct 13
GarlicPlant cloves · Nov 10 – Dec 15
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 6) and first fall frost (Nov 24) 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 78680 came on Jan 30 — about the same time as the 1991–2020 average (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).

Native plants for zone 9a in Texas

640 plants native to the lower 48 states, recorded in Texas, and rated by the USDA to survive 20 °F or colder — the bottom of zone 9a. 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 141

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 208

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 196

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 Round Rock, TX.

Soil in Round Rock, TX

The soil mapped at the center of ZIP 78680 is Oakalla — silty clay loam, well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH8.2alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter4%moderate
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Oakalla silty clay loam, 0 to 2 percent slopes, occasionally flooded.

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 78680; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Round Rock, TX

Summer high97 °Faverage high, August
Winter low36 °Faverage low, January
Hot days112days a year at 90 °F or more
Freezing nights28nights a year at 32 °F or less
Growing degree days6,670base 50 °F — the season’s usable heat
Longest day14 h 08 mindaylight on June 21
Shortest day10 h 10 mindaylight on December 21
Onions to growShort-daysummer days stay under about 14 h 20 min, so long-day varieties won’t bulb
Precipitation37.1 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 60 °F, low 36 °F 60°36° JanFebruary: average high 65 °F, low 40 °F 65°40° FebMarch: average high 72 °F, low 47 °F 72°47° MarApril: average high 79 °F, low 54 °F 79°54° AprMay: average high 85 °F, low 63 °F 85°63° MayJune: average high 92 °F, low 70 °F 92°70° JunJuly: average high 96 °F, low 72 °F 96°72° JulAugust: average high 97 °F, low 72 °F 97°72° AugSeptember: average high 90 °F, low 67 °F 90°67° SepOctober: average high 81 °F, low 57 °F 81°57° OctNovember: average high 70 °F, low 46 °F 70°46° NovDecember: average high 62 °F, low 38 °F 62°38° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 2.77 in precipitation 2.8 JanFebruary: 2.27 in precipitation 2.3 FebMarch: 3.07 in precipitation 3.1 MarApril: 2.64 in precipitation 2.6 AprMay: 4.44 in precipitation 4.4 MayJune: 3.88 in precipitation 3.9 JunJuly: 2.40 in precipitation 2.4 JulAugust: 3.00 in precipitation 3.0 AugSeptember: 3.16 in precipitation 3.2 SepOctober: 3.87 in precipitation 3.9 OctNovember: 2.88 in precipitation 2.9 NovDecember: 2.70 in precipitation 2.7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Georgetown Lake, TX (7 mi away); precipitation: Georgetown 3.0 Ese, TX (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

786829a
Round Rock, TX · <1 mi
786839a
Round Rock, TX · <1 mi
786269a
Georgetown, TX · <1 mi
786749a
Weir, TX · <1 mi
786279a
Georgetown, TX · 5 mi
786738b
Walburg, TX · 6 mi
786349a
Hutto, TX · 8 mi
786659a
Round Rock, TX · 8 mi

All 6 ZIP codes in Round Rock → · Texas planting zones →

Questions about 78680

What planting zone is ZIP code 78680?

ZIP code 78680 (Round Rock, 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 Round Rock, TX?

The median last spring frost (32 °F) near 78680 is March 6; after March 30 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Georgetown Lake station.

When is the first frost in Round Rock, TX?

The median first fall frost near 78680 is November 24, giving a median frost-free growing season of 259 days.

When should I plant tomatoes in 78680?

Start tomato seeds indoors around Jan 9 – Jan 23 and set transplants outside around Mar 13 – Mar 27, one to three weeks after the median last frost.

How much rain and snow does 78680 get?

About 37.1 inches of precipitation a year (NOAA 1991–2020 normals, Georgetown 3.0 Ese station).

How hot do summers get in Round Rock, TX?

The average high peaks at 97 °F in August, with about 112 days a year at 90 °F or more.

What kind of soil does 78680 have?

The USDA soil survey maps Oakalla at the center of ZIP 78680: silty clay loam, well drained, pH about 8.2 (alkaline).

Did spring come early in Round Rock, TX in 2026?

Spring leaf-out near 78680 came on Jan 30 in 2026, about the same as the 1991–2020 average (Jan 29), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Round Rock, TX?

Short-day onions: the longest day near 78680 is 14 h 08 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.

Did the zone for 78680 change?

Yes. The 2012 USDA map put 78680 in zone 8b; the 2023 map puts it in zone 9a. The newer map uses 1991–2020 data and more weather stations.