A two-pronged attack for Bermuda grass

The best defense is to place physical barriers between your garden beds and your lawn areas. Solid edging materials—such as stone and metal—will prevent Bermuda grass roots from advancing. A 3-inch cover of pine straw, bark, or other organic mulching material layered onto your beds will hold the grass back on the surface level, and will also keep down the invasion of new grass from seed. 

The best offense is a combination of mechanical and chemical assaults. Existing patches of Bermuda grass in your beds should be dug out or the soil should be treated with an herbicide like sethoxydim (Poast, Vantage, Super-T, or Fusillade). A pre-emergent herbicide such as Surflan may be used if it is compatible with the flowers and if mulch is not desired. Check the label to make sure that the herbicide is not harmful to desirable plants in the bed. Also, when using herbicides, always follow directions for appropriate uses, application rates and timing, and safety precautions.