Dug edging is free, but time consuming. You can achieve this design by either receding your flowerbed area a couple of inches below the lawn, or by digging a trench around your flower bed. This technique does erode out and will need maintenance.
Plastic is a fairly inexpensive edging style. The plastic typically has a tube-like design, with a base that you place in the ground around the flower bed.
Concrete or brick blocks are inexpensive and long lasting. They don’t provide an elegant design, but accomplish the purpose desired.
Natural stones aren’t uniform or exact duplicates of one another and don’t have perfectly rounded edges. All of these features provide a very natural look to your flower bed. You can go as simple as using rocks from your yard or purchasing elegant stones like flagstone or granite.
Precast edging, typically made of concrete, is available at most hardware stores in a variety of shapes, designs and colors. The pieces typically range from one to three feet in length and fit together to form a consistent edge around your flower bed.
Wood provides a natural look to your flower bed, in a more casual style. It’s great at holding mulch in position, but since it is biodegradable, is not entirely weed resistant.