Push a shovel down into the ground using your foot until it is fully underneath the roots of the ornamental grass. Pull up on your shovel like you are scooping out the grass until the ornamental grass comes up. Ornamental grass should come out in large clumps.
Shake the soil from the roots of the ornamental grass and toss it into your wheelbarrow. Dispose of the grass in the trash or compost pile.
Spray weed killer directly into the soil as close as you can get to the roots of the ornamental grass until they are completely soaked. After about 2 days the ornamental grass should be dead. Mow over it with a lawn mower to cut it down completely or remove it by digging it up by the roots with a shovel.