It's necessary to remove grass where you plan to make a new flower bed. Once the grass is removed, use herbicides to prevent the grass from returning. Keeping grass under control is easy if you know the proper procedures.
Edge the flower bed so that it is separate from the the lawn. Use a garden hose to mark the line where you want the garden bed to be. Dig along that line with a sharp spade shovel or sod cutter.
Remove the grass in the designated flower bed using a sod cutter or straight-edged shovel. Moisten the soil and the cut the grass into 3-foot long strips.
Pry up the strips of grass in the flower bed with the shovel. Loosen the soil with the shovel when the grass has been removed. Mix in organic material such as compost, dead leaves, peat moss or manure 6 inches into the soil.
Continue managing the flower bed by growing any seeds you'd like. If small patches of grass appear in areas of the flower bed, uproot them by hand or use a sod cutter.
Apply a herbicide to the grass if it continues to grow in large amounts. A beneficial herbicide for grass is Preen. It will permanently kill the grass.