Triple Trellis, White by Structures. $6.99. material: Metal. Color: White. size: 6.5" Wide x 7" High. A trellis is a functional structure often used to support plants, but a triple trellis goes beyond this definition. With its curved arches and straight lines, the triple trellis makes a statement in the garden by providing an interesting backdrop to your landscape. The trellis comes in a white or antiqued finish.