Cut a piece of cardboard to 5 inches wide. The length of your piece can be anywhere from 5 to 8 inches, whatever is comfortable for you to handle.
Wrap your yarn around the card, making sure that the cardboard remains flat and does not curl.
Cut one side of the looped yarn. Each piece of of yarn will be 10 inches long, and the number of pieces of yarn you will need is two times the number of stitches wide your afghan is. For example, if your afghan is 220 chains wide, you will need 440 pieces of yarn.
Place the crochet hook through the first stitch on the bottom of your afghan. Fold one strand of yarn in half, forming a loop in the middle. Place the loop over the hook and gently pull the loop through the edge stitch in the afghan. Pull only one side of the yarn through so that there is one-half of the piece on each side of the afghan. Confirm that the yarn is equal on each side. Tie a knot in the yarn.
Repeat Step 4 above until each stitch on the edges of both the top and bottom of the afghan has been tied with a fringe.