Once grass invades a flower bed, it's tough to get out. The tough roots and creeping runners can take over if left unchecked. When fighting grass in flower beds, you have to be careful not to kill the flowers. Successfully eliminating grass in flower beds may involve several different approaches, implemented at different times of year. Once the grass is gone, you can take steps to keep it from coming back.
Weed the flower bed by hand. This approach works best in early spring, while the grass is still young and immature. Choose a day after it has rained, or water the bed well before you begin to weed. Wear gardening gloves and work your fingers down into the soil to yank the grass out by the roots. Or use a fork or special weeding tool to uproot the grass.
Spray a weed killer. This method works well in an annual bed before you've planted annuals. You can spray the entire bed with a weed killer such as Round Up. Wait twenty-four hours before you transplant seedlings to the bed. You can also use weed killer in a perennial bed or other flower bed with established plants, but you must be careful not to get the weed killer on any part of the plants you want to keep. Choose a still day for spraying the weed killer and use a piece of cardboard as a shield to protect plants as you spray. This will help you get rid of patches of grass between plants, but you may still have surviving grass at the base of flowers.
Lay down a weed barrier such as weed cloth, newspaper, cardboard or a thick layer of mulch. Cut holes in the material for existing plants. These barriers deprive the grass of light and will eventually kill it, though you may still have stubborn shoots peeking up at the base of existing plants.
Trim grass around flower beds regularly with a string trimmer. This will keep grass runners from extending into the flower bed and taking root.