How do you join crocheted granny squares to finish off edge?

When you need to change skeins of yarn while you are working your project, it is best to do it at the end of a line. I would overlap three or four inches of yarn at the end of one skein and the beginning of the other. Make several stitches with the doubled yarn.

If it looks too bulky, you can always tie a knot in the yarn at the end of the row. Never tie yarn in the middle of your work, it looks bad, and will create a interruption in your work.