There will be times when you need to add stitches to a row. Sometimes that comes at the end of a row, perhaps to create a sleeve. Sometimes you need to add stitches mid row, when you are creating buttonholes, adding underarm stitches to a body worked top down or perhaps you are knitting hand warners or socks. I prefer a knitted cast on, this method is more stable and gives a first row to the portion you are creating.
Here's a look at the my steps to doing a Knitted cast on
