This is how I finished off the picot edge on the toe up socks in the previous entry. I tried plain sewing and didn't like how the stitches ended up twisted. In an attempt to sew them down flat and keep the stretchiness, I came up with this. It's sort of like the kitchener stitch in that you're sewing through the live stitches twice. That is what makes them lay flat. Here we go...
Click pictures to see a slightly larger version.
Cut the yarn and leave a really long tail for sewing down the free stitches.
Insert the sewing needle into the first stitch purl-wise and keep the yarn underneath the knitting needle. Keep that stitch on the knitting needle.
Hold the sewing needle pointing towards the picot edge. Insert the sewing needle under a purl bump and pull the yarn through. Keep all yarn underneath the knitting needle.
Insert sewing needle knit wise into the first stitch on the knitting needle. Keep yarn underneath the knitting needle. Pull that stitch off of the needle.
You can see how it looks a bit loose in the picture below. I tighten this up before starting the next stitch.
This is what the finished section looks like. The live stitches are are dark grey. The purl bumps are pink. The yarn that I was sewing with is white.