Planting straight-edged borders on the edges of a garden can sometimes be the right option, and can deliver a clean, modern design. But don't make these too narrow, or they can look a little meager.

Mexican architects from Estudio 3.14, a design firm based in Guadalajara, imagined a hot pink border that stretches 1,954 miles, called the "Prison-Wall.". The renderings are meant to show the ...