One way to keep the lawn from creeping into your flower bed is to edge the bed. Often, people do not want to go through the expense of placing edging borders around the flower bed. The alternative is digging an edge in a flower bed to create a distinct separation between the lawn and the bed. The key to digging an edge is to have a straight edge along the lawn side of the trench. This straight edge serves as a barrier, preventing the grass from growing into the bed.
Mark off where you want the edge of the flower bed. If you want straight sides around the flower bed, drive wooden garden stakes into the ground with a hammer and tie string from one stake to another. Spray the line onto the ground with gardener's spray paint, if you desire more curves to the outline of your flower bed.
Stand on the lawn side of your line and insert a garden spade straight into the line. A garden spade is a smaller shovel with a square head. Press your foot on top of the shovel head and insert it 4 inches into the ground. Lift the garden spade out of the turf.
Continue inserting the garden spade straight into the line 4-inches and bringing it back out of the ground. Repeat until the entire line you planned is now cut into the soil.
Go to the flower bed side of the line and place the shovel head 4-inches away from the first dig. Angle the head at a 45-degree angle. Push the shovel through the soil with your foot up to the bottom of the first dig. Remove the dirt, creating a 45-degree wedge. The lawn side of the wedge should be straight.
Dig around the entire perimeter of the flower bed removing the 4-inch wedges and placing the soil in a wheelbarrow. Use the soil in the wheelbarrow to fill low spots in your yard.
For a decorative effect, pour pea gravel or river rocks into the wedge-shaped space along the perimeter of the trench.