Adding a Greenhouse to a Garden A simple framework of hoops and a lightweight cover can extend your growing season. . . . Use galvanized pipe straps to mount 1-in. PVC pipe inside the bed walls. Cut ½-in. flexible PVC tubing twice as long as the beds' width. Bend it, mount it and clip a cover in place. Use clear polyethylene film to raise soil and air temperatures in early spring. –“How to Build Raised Garden Beds,” Fiona Gilsenan How does the diagram support the purpose of the document? It illustrates the placement of materials to make the sequence of tasks clear. It restates the purpose of the text. It illustrates additional ideas for enhancing a garden bed. It shows what could happen if the reader made a mistake in the placement of materials.