Grass belongs in your yard, not in your garden. But certain grassy weeds like couch grass and crabgrass frequently creep from the lawn into the flower bed. When you see grass in your flower bed, it's best to treat it immediately. A small patch or two along your flower garden's border can quickly take over your flower bed, and a large colony will deprive your flowers of nutrients and water.
Water your flower garden. It is easier to pull weeds out of wet soil.
Pull up as much of the grass and its roots as possible, but take care not to disturb your flowers' root systems. Certain annual types of grassy weeds may be controlled by pulling alone.
Spray the grass with a selective post-emergent herbicide prescribed for use on the type of grass that is growing in your flower garden. Spraying can be done instead of pulling, or in case the grass comes back after it is pulled. Spray on a day when there is no wind (and no rain forecast for the next 48 hours) to minimize the possibility that you will accidentally spray your plants.
Respray the grass at the interval dictated by the herbicide's manufacturer. New patches of grass may die after the first spray, but older stands of grass may need to be sprayed two to three times before they die.
Remove the dead grass from your flower garden.