|I live in Las Vegas, Nevada. My zone number varies between zone number 9, 10, or 11, depending on the source. Please tell my the correct zone number. Also, do azaleas or purple wisterias do well here with extra care? All the nurseries sell them here.|
|According to my map, it looks like you are in USDA zone 9b; this simply means that your average lowest winter temperature is between 25 and 30F. USDA zones can help you determine if a plant is hardy in your region, but doesn't necessarily tell you what wil thrive.
A better guide might be the zones developed by Sunset Publishing, in their "Western Garden Book". These zones are based on not only winter temps, but also rainfall, elevation, etc. According to this book, you are in Sunset zone 11. Your hot summers and cold winters can be a challenge for many plants.
Rhododendrons and azaleas like moist soil, humid air, and acid soil. It would be difficult for you to provide these conditions, so they probably wouldn't thrive unless you took some extreme measures, including amending the soil with lots of organic matter, and, if necessary, sulfur, to lower pH. Frequent watering and protection against drying winds are also important. Wisterias are grown throughout the West. They may suffer in alkaline soils, so a soil test is important.