St. Augustine grass is a warm-season grass found along the Gulf Coast and other parts of the far southern United States. St. Augustine grass spreads rapidly from creeping stolons which spread out and root into the ground to form new grass plants. This enables St. Augustine grass to spread into areas that it is not desired like garden beds. St. Augustine grass does not spread via underground rhizomes like Bermuda grass. This makes controlling the grass much easier and deep landscape borders are not needed.
Purchase your choice of garden edging from your local home improvement store. Some types include plastic, aluminum and steel.
Dig a trench along the edge of your garden that is 3 to 3-1/2 inches deep. Dig it so that it's wide enough to slide the edging down into. Cut the edge that faces your lawn vertically with a garden spade to provide a nice, clean edge.
Unroll the garden edging and install into the trench, with the edging 1/2 to 1 inch above the top of the soil.
Backfill the soil into the trench around the edging. Keep the edging flush with the side of the trench that has the straight, vertical cut. Tamp the soil down to ensure the edging is secure.
Trim the grass around the edging with a weed eater each time you mow. This will prevent the grass from slowly creeping over the top of the edging.