USDA hardiness zone 9a
In zone 9a, the coldest night of the winter averages 20 to 25°F (−6.7 to −3.9°C). That is the lowest temperature of each winter, averaged over 1991–2020, on the 2023 USDA Plant Hardiness Zone Map.
20 to 25
°F, average coldest winter night
−6.7 to −3.9°C.
2,199
ZIP codes in zone 9a
5.5% of the 40,326 ZIP codes on the map.
Cities in zone 9a
Same zone, different springs: the typical last frost is Jan 24 in Las Vegas and Mar 8 in Seattle, about 6 weeks apart.
| City | Last frost · typical | First frost · typical | Zone from ZIP |
|---|---|---|---|
| San Antonio, TX | Feb 25 | Nov 28 | 78201 |
| Seattle, WA | Mar 8 | Nov 23 | 98121 |
| Las Vegas, NV | Jan 24 | Dec 10 | 89129 |
Other larger places in this zone, by the ZIP nearest their center: Austin, TX; North Las Vegas, NV; Baton Rouge, LA; Tallahassee, FL; Mobile, AL; Santa Rosa, CA; Charleston, SC; Bellevue, WA.
Frost dates are the typical dates of a 32°F freeze from NOAA’s 1991–2020 climate normals; each city page also gives a safer date. Zones can vary within a city.
What zones do and don’t tell you
What a zone tells you
How cold winter nights usually get: the lowest temperature of each winter, averaged over 1991–2020. Gardeners and nurseries use it to judge whether a perennial, shrub or tree is likely to survive the winter. It is an average, so some winters still get colder.
What it doesn’t
When to plant. Two gardens in zone 9a can have their last spring frost weeks apart, because frost dates depend on elevation, nearby water and how fast spring warms up, not on the coldest night of winter. The zone says nothing about summer heat either.
For planting dates
Vegetables, herbs and annual flowers are timed from frost dates. We give them by ZIP code, from the nearest NOAA weather station. Find your frost dates
Hardiness zones: 2023 USDA Plant Hardiness Zone Map, PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 9 Nov 2026.