Plastic edging is one of the most common forms of edging used for landscaping borders. The edging helps to keep grass runners and other weeds out of your garden beds, while at the same time holding mulch in place. Plastic edging comes in three types: rolled edging, plastic fencing and plastic stones. Always buy high-grade commercial plastic edging. Lower quality, less expensive edging will break down more quickly and is subject to frost heave.
Dig a trench around the perimeter of your landscaping bed with a spade and scoop shovel. The trench should be 6 inches deep on the outer edge and slope downward from the landscaping bed on the inner side. Cut any roots you encounter. The edge of the trench must be a clean, 6-inch line extending around the bed.
Unroll the edging and shove it up against the outer edge of the landscaping bed. Edging is typically sold in 20-foot sections. Join the sections using plastic connectors. Insert one side of the connector halfway into one side of the edging and do the same on the other side of the edging. Do not push the connector fully into the first side in your attempt to slide the second half into the second side. Cut the edging to fit the landscape border with a utility knife.
Position the edging so that only the top one-third of the plastic is visible above the soil line. Rolled edging should not look like a plastic hose sitting above the ground. If it does, you have set the edging too high. Push the V-shaped bottom end of the edging into the loose soil at the bottom of the trench so the edging sits at the proper height. Stomp on any curves so the edging is forced into place instead of being flattened against the trench.
Insert the metal stakes into the bottom of the edging above the V-shaped curl in the plastic, so that the stakes are parallel to the ground. Use four stakes for each 20 feet of edging. Pound the stakes into the ground, keeping them parallel to the soil line.
Fill the trench in two-thirds of the way with soil behind the edging. Stomp the soil in behind the edging to force it into place around the bottom and prevent frost heave in winter from forcing the edging upward.
Sift loose soil into the cracks between the outer edge of the edging and the lawn. This will give lawn grass a place to grow to fill in the cracks where the edging and the lawn don't quite meet.
Water the edging to settle it in.
Fill in behind the edging with soil so the bed is even with the rest of the lawn.