Planter Box/Trellis/Retaining Wall This cedar bambo combination solved three problems for the home owners. It holds up the hillside with three posts buried deep into the ground and large pressure treated boards, it provides an area to plant roses where none existed and it works as a vertical and horizontal trellis. The construction was of pressure treated framing with cedar and bamboo overlay. The trellis was made of tam vong solid pole bamboo.