Deconstruct SunRound Rock, TX: Hardiness Zone 9a & Sunlight by Season
Round Rock is in USDA hardiness zone 9a. Here’s what that means for winter, plus sunrise, sunset, daylight hours and the sun’s path through the year.
Zone 9a in Round Rock
On the 2023 USDA Plant Hardiness Zone Map, Round Rock falls in zone 9a. That means the coldest night of a typical winter drops to between 20 and 25 °F. Perennials, shrubs and trees labeled for zone 9a or colder (a lower number) should survive the winter here.
A zone only covers winter cold. For a plant to do well it also needs the right amount of sun, and that varies far more from one corner of a yard to the next than the zone does across town.
This is not the official USDA Plant Hardiness Zone Map. Zones are derived from the official 2023 dataset, resampled to about 2 km.
Nearby cities
- Austin, TX Zone 9a
- Killeen, TX Zone 8b
- Waco, TX Zone 8b
- College Station, TX Zone 9a
- San Antonio, TX Zone 9a
- The Woodlands, TX Zone 9a
- Houston, TX Zone 9b
- Arlington, TX Zone 8b
The sun over Round Rock
On the June solstice the sun rises in the northeast at 6:28 AM and climbs to 83° above the horizon at 1:32 PM. On the December solstice the noon sun reaches only 36°, so a 20-foot tree casts a noon shadow about 27 feet long. In June the same tree’s noon shadow is only 2 feet.
Sunrise, sunset & daylight by month
| Date | Sunrise | Sunset | Daylight | Noon sun |
|---|---|---|---|---|
| Jan 21 | 7:26 AM | 5:57 PM | 10h 31m | 40° |
| Feb 21 | 7:05 AM | 6:23 PM | 11h 18m | 49° |
| Mar 21 | 7:33 AM | 7:42 PM | 12h 10m | 60° |
| Apr 21 | 6:56 AM | 8:02 PM | 13h 06m | 72° |
| May 21 | 6:32 AM | 8:22 PM | 13h 49m | 80° |
| Jun 21 | 6:28 AM | 8:36 PM | 14h 07m | 83° |
| Jul 21 | 6:42 AM | 8:31 PM | 13h 50m | 80° |
| Aug 21 | 7:01 AM | 8:06 PM | 13h 05m | 71° |
| Sep 21 | 7:18 AM | 7:28 PM | 12h 10m | 60° |
| Oct 21 | 7:37 AM | 6:52 PM | 11h 16m | 49° |
| Nov 21 | 7:01 AM | 5:31 PM | 10h 29m | 40° |
| Dec 21 | 7:23 AM | 5:34 PM | 10h 10m | 36° |
Local time (Chicago), including daylight saving time. “Noon sun” is the sun’s height above the horizon at solar noon.
Daylight through the year
What “full sun” means in Round Rock
Full sun is 6+ hours of direct sun. In Round Rock an open spot has 14.1 hours of daylight to work with in June and 10.2 in December, so a bed that clears 6 hours in summer can easily drop to part shade in winter once the low sun slips behind trees and houses.
Measure the sun in your Round Rock yard
Daylight is the ceiling. Deconstruct Sun traces the trees and buildings around one exact spot and tells you its real direct-sun hours, today and at every solstice and equinox.
Questions
What hardiness zone is Round Rock, TX in?
Round Rock, Texas is in USDA plant hardiness zone 9a on the 2023 map. The average coldest winter night is 20 to 25 °F (−6.7 to −3.9 °C).
How many hours of daylight does Round Rock get?
About 14.1 hours on the June solstice (sunrise 6:28 AM, sunset 8:36 PM) and 10.2 hours on the December solstice (sunrise 7:23 AM, sunset 5:34 PM). Around the equinoxes it is close to 12 hours.
How many hours of sun does my Round Rock yard get?
Up to the daylight hours above, minus whatever trees, buildings and fences block. In winter, when the sun stays low, that can be most of it. The Deconstruct Sun iPhone app measures the real direct-sun hours for one exact spot by having you trace what is around it.
When is the best time to plant in Round Rock?
Zone 9a tells you which perennials survive winter, not planting dates. For timing, use your local average frost dates from your county extension office, and choose plants rated for zone 9a or colder.
Source: USDA Plant Hardiness Zone Map, 2023. Agricultural Research Service, U.S. Department of Agriculture, planthardiness.ars.usda.gov. Underlying data © PRISM Group, Oregon State University, prism.oregonstate.edu, accessed 2026-08-30. Sun times calculated for 30.526, -97.663.