Couching is simply sewing a heavy thread in place with a finer thread. It works beautifully by machine as well. I use a zigzag stitch to secure the heavy thread in place. And, if you have a cording foot— the foot guides the thread as you sew.
How To Sew A Perfect Round Hem .not everybody has a serger or like the idea of the bias tape. That is why I wanted to add this tutorial with a simple way to make a round hem. - More tips for curved hemlines.