Just planted: A straight and narrow walkway down a sunny south-facing side yard in north central Texas. Walkway itself is flagstone surrounded by river rock. Both sides are lined with metal edging. I've just put into the ground perennial, drought-tolerant plants, including Mexican hair, yellow yarrow, blue fescue, lambs ear, purple oxalis, orange and pink lantana, purple verbena, and white alyssum. White and purple clematis are in pots with metal trellises. Next step is to apply mulch.
Landscape Edging: 10 Easy Ways to Set Your Garden Beds Apart: EverEdge Edging - Made from sturdy, powder coated flexible steel with 3-3/4" spikes, EvrEdge appeals with its casual, country garden look. Lengths are interlocking for seamless installation and come five to a set, totaling 16 linear feet of edging per package. $95 at Grandin Road
Steel Steel edging is a very common landscape option, but depending upon your choice of color, it can make very different statements. Black steel edging looks more formal; green and brown are more traditional. It also comes in a range of thicknesses, with the thicker material being more expensive (and more durable) than the thinner edging. Cost: $2.50 to $4.50 per linear foot.
River stones used as an accent with a metal edge adds visual interest to an otherwise simple setup. The metal edging keeps the stones from spilling over into the landscape, and it also keeps the landscape from crossing over onto the pathway.