Learning how to kill grass in a flower bed involves understanding how grass grows. Grass throws deep roots into the soil to gather moisture. These deep-seated roots can prove difficult to remove when creating a new flower bed. Plants in a flower bed cannot compete with grass for essential nutrients and moisture. Applying spray herbicides to the grass can cause the loss of flowers, since the treatment may soak into the soil. The correct and complete removal of grass using simple gardening tools will help the flower bed appear groomed and prevent the encroachment of grass into the garden in future years.
Place the spade shovel at the edge of a clump of grass. Step down with your full weight to drive the shovel deeply into the soil. Dig deeply to a depth of 8 to 10 inches since grass roots travel deeply into the ground.
Scoop out the entire mass of grass and roots. Shake off excess soil and discard or use the clump as repair grass for a bald spot in the lawn.
Proceed throughout the garden, removing additional clumps of grass by digging deeply into the soil.
Address encroaching grass at the edge of the garden by placing the open side of shovel blade towards the flower bed. Step down and create an edge along the length of the garden border that meets the lawn. Creating this edge will discourage grass from growing into the flower bed. Edge regularly two to three times during the growing season to keep the garden edge sharp. Remove smaller grass clumps as soon as they appear.
Monitor the appearance of any new grass in the flower bed. Dig up any stubborn grass that continues to appear. Dig as deeply as possible to remove trailer roots.
Kill stubborn grass by applying a layer of folded plastic sheeting to the top surface of the garden. Avoid placing the plastic over any existing plants.
Drive stakes around the edges of the sheeting to secure the plastic to the soil. Leave the sheeting in place for four to six weeks to completely smother stubborn grass.