After the garage construction, we had some left over Trex “composite lumber” decking. It has become the edging material of choice here in my garden.
It looks appropriate for an urban garden: simple and modern when the faux wood grain side is turned away. This color plays well with the terra cotta colored brick of my house. (The house in the photos is my neightbor's but her brick is similar). It is not going to rot, being part wood waste and part recycled plastic. Barring any sloppy driving incidents, it will stay indefinitely just as it was put. Unfortunately you must pay dearly for these qualities, at $2 a lineal foot!
I justified the cost in tires not punctured, as I pulled out the deformed existing steel edge.
There are cheaper composite lumber materials available for edging, like Rhino Edge and Bend-a-Board. Since we already had part of what was needed, I decided not to change materials.
The corners were mitered, without loss of body parts, and two steel angles were installed to hold each corner together.
There is a corner running into the slope at the end of each side, for stability and to finish off what would otherwise be a loose butt end. (This is a gentrified neighborhood, thank you.) On the long runs, the Trex is set down in a groove adjacent to the sidewalk, and this combined with the angles at the corners provides all the stability it needs.
With the front and part of the back garden edged with Trex, I am looking at using it to shape the vegetable beds…coming soon! (Project number 29 out of about 5000)