Get a sturdy material with an open weave to use as the foundation for your shag rag rug. Its size determines the size of your rug. Burlap or monk's cloth can be used as the base material. Monk's cloth is a heavy cotton material, and its threads are less prone to breaking as fabric strips are pushed through it.
Choose a material that is woven tightly for your fabric strips. The tight weave will help prevent fraying and make your shag rug more durable. You can cut up old wool blankets or buy new wool flannel to create your strips. Old denim and other dense cotton fabrics can be used as well.
Select a prodder that feels comfortable in your hand. Traditional prodders often have thick, rounded handles with pointed tips for pushing fabric strips through the base material. However, you could use a size 10 knitting needle as a prodder instead.
Plan your rug design on paper, deciding how you will intermix the fabric strips by color and fabric content. Sometimes shag rag rugs are created from a single fabric or include a series of alternating stripes. If you decide to use any motifs in your design, draw them on the wrong side of the base material with a permanent fabric marker.
Cut your shag fabrics into strips that are 3/8-inch wide. The strips should be no shorter than 2½ inches and no longer than 4 inches. Longer strips create a shaggier appearance.
Sew a 1-inch hem all the way around your foundation material before you begin working to prevent it from fraying. When pushing the fabric strips through the area of the hemmed edges, go through both layers created by the hem.
Use your prodder or knitting needle to make a hole on the wrong side of your base fabric, and push a fabric strip half-way through the hole. Make a second hole that's about 4 threads away from the first hole, and push the other half of the strip through that hole. The 2 ends of the strip should now be protruding evenly on the right side of the fabric base. The wrong side of the base material, which is facing you, should show the strip lying flat against it.
Decide whether the second hole of the first strip will be used as the first hole of the next strip. Alternatively, you can begin the first hole of the second strip about 4 threads away. The thickness of the strips affects placement, and placing them too close together can cause the base fabric to pucker. Continue adding strips until your shag rag rug is complete.