1. USE A SHARP SPADE OR SHOVEL TO CUT STRAIGHT DOWN SEVERAL INCHES INTO THE SOD all along the edge of the bed. (if the bed has been mulched, rake back the mulch before you start cutting.)
2. MAKE 45-DEGREE CUTS BACK TOWARD THE FIRST CUTS, as shown, and lift out the wedge-shaped sections of sod and topsoil, leaving a shallow trench. Shake as much soil as possible out of the sod and back into the bed, but don't let it refill the trench. This sprinkling of loose topsoil will give the bed an attractive, freshly cultivated look. Let the remaining sod dry out for a few days to kill it; then add it to your compost pile.
3. APPLY MULCH ALONG THE EDGE OF THE BED, being careful not to let it fill the trench. When lawn-grass roots grow toward the bed, they will be stopped by the straight side of the trench. You can mow the grass cleanly by guiding the mower so that it straddles the trench and two wheels roll along the mulched edge of the bed. it helps to site your plants back from the edge just far enough to leave room for the mower.
A spade with a straight cutting blade works well for edging beds, but it should be sharp enough to cut through the sod easily. A shovel with a pointed tip cuts into the sod more easily than a spade does, but a spade makes a neater trench. If you have a large number of beds to edge, you might want to try a special edging tool that has a half-moon-shaped blade that you rock back and forth as you push it into the sod with your foot.