USDA Zone 9 In Texas, zones 9a and 9b extend along the southern tip of the state and the Gulf Coast. From Del Rio to Galveston and Beaumont. Temperatures in this area are usually mild. Frosts are rare, with average minimum temperatures of 9a between 20 and 25 °F and 9b between 25 and 30°F.
The coldest area indicated by the USDA Texas planting map is 6b, located in the northern part of the state. The rest of Texas enjoys very warm weather all year round, including the winter months. The remaining areas of Texas include zones 7a, 7b, 8a, 8b, 9a, 10a, and 10b. Winter lows may drop -5 degrees F.
Or set a temperature of up to 20 degrees F. While the Texas zone map doesn't guarantee that plants will survive, it does provide a very solid framework for planning a garden.