Some say November 12th and some say November 15th so between the 12th and 15th is the best average date.

Of course, we have had it before Halloween and after the first of the year but for planning and planting purposes, these are the average dates we go by.
From Parker County Extension Agent Agriculture, Jon Green

Special Note:  Garden in March with the average last killing frost date for our area in mind. Our last average killing frost date is March 17th. Killing frosts can occur after this date but it is a good indication.