A ridge stitch in knitting is a method of alternating stitches per row for a textured pattern. Knit a ridge stitch with tips from a knitting teacher in this free video on yarn crafts.
So we've talked about the seed stitch and the moss stitch, which you're alternating the stitches and your knitting your purls and purling your knits. We've done the rib stitch, where you're working your knit two and purl two to make your alternating stitches but you can also alternate that knit and purl in your rows. So, if you were going to do something like a ridge stitch, you would knit across two rows and then after that you would have a purl row and then if you go back across one of your purl sides and knit, you'll get a ridge on the front. So, now I've got stockinette, right here, and now if I knit on my purl side, it's going to give the affect of a ridge on the other side and this can be a pattern stitch in a garment where you knit a row, purl a row and then have two rows of knitting, which I've just cut down to size. So, when you finish that you've got your stockinette and your rib and if you carried on this way, you'd have a couple rows of flat knitting and then you'd have a ridge and that's a way you can alternate your stitches by rows instead of by stitch by stitch.