A pattern I have says in the finishing to "tack the hem". The hem is made on the stockinette stitch piece by putting a purl row, then 4 knit rows (this is worked in the round). The hem then turns on the purl row, but how do I "tack" the hem? I tried a whip stitch, but that makes a very tight bottom that does not give or stretch at all. So there has to be a way. I've not made too many pieces with hems, usually hats, and they don't seem to suffer any side effects from a whipped stitched hem.