If it is St. Augustine a simple piece or metal or plastic edging will do. If you grass is Zoysia you may need to extend a barrier of some type 4 inches deep into the soil. If it is bermudagrass the barrier should go 6-8 inches deep. This may be impractical to do leaving you with the task of "defending the border" with a herbicide effective against grass. Some products are selective for grass and are not as damaging to most ornamentals. They contain one of the following ingredients: fluazifop-P-butyl (Fusilade Ortho Grass-B-Gon and Ornamec are example brand names) or sethoxydim (Poast is one brand name). Herbicides containing glyphosate (Round-up, Klean-up, and Weed-Away are example brand names) will also work but kill most any plant contacted by the spray.
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