Every now and then someone will ask a question on a forum and someone else will ask, "where do you live?" The original poster may respond that he/she lives in USDA Zone 9a. Let me show you why it is helpful to have a more precise location.
Here is a picture of the USDA zones in the south central part of the US, specifically Texas and Louisiana.
Zone 9a is the light brown zone that extends west from New Orleans and the Mississippi Delta along the Gulf coast and across South Texas to Mexico. The problem is that the Mississippi Delta area gets 90 inches of rain per year and the South Texas desert gets 10 or less per year. Also the Mississippi Delta high summer temps are occasionally in the low 100s while the Texas desert temps can run between 110 and 115 for days at a time. The desert low temps can remain in the 100s for the night. Plants that grow easily in Louisiana will not grow in South Texas.
Another problem is the soil. This zone skips Alabama and starts again in Florida to the east. The South Texas soil is limestone with a pH of 8.0 and the Florida soil is either sandy or more organic with a pH down in the 6's. These problems are in every zone. Zone 6, for example, extends from New Jersey to Alaska. In Southern California some of the zones are only about one mile wide.
The USDA hardiness zones try to combine annual low temperatures, high temperatures, and soil types but there are still many more important things to consider. Thus the zones have been simplified to be based on the winter low temperatures. However, the rest of these factors are important when making choices for your turf grass seed or variety. It is understandable that to make a map like this, some compromises had to be taken into account. It makes a nice picture but it is not that informative when you need help with your lawn.
For these reasons, it is better to tell where you live so others can help you with your specific lawn issues. If you are asking about specific grass seed varieties, sod selection, or even watering recommendations, knowing where you live becomes very important.
When you sign on to the Bestlawn.info forums, you will be asked for your location. Please be specific with the state and the city or town nearest you.