It is mainly a design meant for outdoor purposes, made up of either wood or cast iron. Wrought iron trellis are also a popular choice. They are used for decoration, and gives your garden a unique and tranquil look. Garden Trellis Ideas Please note: You are currently browsing img 25 best images about garden trellis on pinterest that is 736x981px in size. This image is listed in garden trellis decorations category. Garden Trellis Ideas, 736x981 in 183.72 KB.