One way to separate the flower bed from the lawn is to install plastic lawn edging. Many times people install lawn edging incorrectly. Installing plastic lawn edging properly will enable you to cut your lawn without fear of damaging the top of the edging. Quality edging comes in 20-foot lengths, and also has connectors that join pieces together. The top of the edging has a bubble edge, while the bottom has a V bend that helps keep the edging straight while installing. For long-term installations, use a good-quality commercial-grade plastic lawn edging.
Dig a trench around the area you want the edging with a square spade shovel to a depth 1 inch less than the width of the edging. This will create a soil wall for the edging to lay against. If you are installing edging between the lawn and garden, move the dirt from your digging into the garden while throwing out the clumps of grass.
Rake the soil away from the soil with a garden rake. Create a 6-inch area away from the soil wall to work the edging into place.
Place the plastic lawn edging against the soil wall with the curled V portion at the bottom and pointing away from the soil wall. Bend the edging around the contour of the soil wall. Insert flat edging connectors to join two pieces of edging together. The ends of the edging slide into the ends of the connectors. Cut the edging as necessary with a serrated knife.
Pack soil loosely around the bottom edge of the edging and tamp down slightly with your foot. Inspect the distance of the top of the edging to the ground. You want the top of the edging to be no more than 1 inch above the ground. Place soil under the edging if necessary to raise the edging in certain areas.
Place an edging stake into the edging 3 inches from one end of the edging and 1/3 up the width of the edging. Hold the stake as flat as possible with the head of the stake pointing away from the soil wall. Pound the stake through the edging and into the soil wall with a hammer. Use four stakes for every 20 feet of edging. Always use a stake on each end of edging pieces.
Pack soil firmly 2/3 of the way up around the edging, using your foot or a wooden board. Water the soil around the edging with a garden hose to help pack the soil.
Move more soil around the edging until the soil is 1 inch below the top of the edging. Tamp the soil firmly with your foot or a board.