What is the frost depth line in San Antonio Texas?

San Antonio is in the USDA hardiness zone 9a with an average annual minimum temperature of 30° F. According to the local frost date information, the latest frost date in the Spring is March 15 and the earliest frost date in the Fall is November 15. That means the frost-free period in the area is about 245 days. The frost-depth line is typically defined as the maximum depth at which the soil will freeze during the coldest day of the year. Since San Antonio is in a Mediterranean climate zone with hot dry summers and mild winters, the ground rarely freezes, and there isn't a frost depth line.