Here's an organic way to keep weeds out of your lawn: Nature's Guide Corn Gluten Meal is a fine yellow powder that interferes with the germination of seeds. Put down Corn Gluten Meal early in the Spring (depending on the weather, between February 15 and March 15 in the Fort Worth area) and in the Fall (again depending on the weather, September 15 through October 15) and it'll keep the weeds out. It's also a great early season fertilizer.
Apply at a rate of 20 lbs. per 1000 sq. ft. Water in thoroughly then allow soil to dry out for several days before resuming your normal watering schedule. You'll see better results each year that you use it!
The spreadable version of the product doesn't cover as well as the meal version, but it is easier to apply. Both types provide an a natural nitrogen fertilizer.
Corn Gluten Meal is a by-product of corn processing. A completely natural residual product with 9% nitrogen content. Corn Gluten Meal has no effect on post emergent weeds or perennial weeds.