Identify which ornamental grass plants need to be trimmed. You only need to trim plants that are overgrown into walkways or that are crowding out other plants.
Gather all of the blades of the ornamental grass plant together and tie them in a bunch using a piece of string, rope or twine. Place the rope or twine between six and ten inches above the base of the plant. The exact height depends on how close the plant is to other plants. However, do not cut the blades lower than six inches above the base of the plant.
Using sharp pruning shears or other cutting tool, cut through the ornamental grass directly below the string or rope.
Take the upper cut off section that is still tied together and discard into a compost pile or into the trash.