This is the way I use to close by hand a machine knitted piece. This method can be used for hand knitting too, of course.
Generally, if you don't use some special starting stitch (that I'm still looking for; sometimes I use crochet work, given that I'm good with crochet), machine knitted piece remains open at tha start.
To avoid the good work from undoing, I use to do some rows with a scrap yarn. You'll undo these rows once the machine knitting is finish. (And again: this is not my original idea, my Mom taught me this!)
But you need to close the first good row in the work.
Sometimes I've asked my sister (who is really really good in hand knitting) to close it for me, but she said that, if you close the work the "traditional way", it will be not stretchy.
As you all of course know, it's really comfortable to have stretchy edge.
So I found this way to close the work that is both simple and elastic!
Step 1: Do Your Piece
Start with a normal row with knitting machine using scrap yarn and put the nylon thread to block it. (A woman once said to me that it was not necessary because it will be blocked automatically: I can't do that without the nylon yarn and the woman didn't say to me how she did it.... So I go on doing that).
Do 2-3 rows like that, than pull out the nylon thread and go on for more 2-3 rows. The first 6-8 rows are needed to avoid the good part to undo while you work on it.
Change yarn and work with the good one to do the piece you need. Cast off.
Using a double pointed knit needle (the one you need for cables), put on the stitch of the starting hem. You are putting the work on the needle upside down. I prefer to do this work on the wrong side of the piece: do some samples to decide what you prefere.
You can put all the stitches on or do it with some of them and put the remaining ones after you start closing.
You can use a double pointed knitting needle thinner than the one you'd use for the normal work because you won't, in fact, use this needle for work. It is just to have the stitches neat and tidy.
Do not undo the scrap work now!
You need a double point needle because you put the stitches on the left point and sew them from the right (if you are right handed like me, the other way if you are left handed).
Thread a tapestry needle, then repeat these steps until you finished off all the stitches:
- from right to left, pass the needle in the two first sticthes on the right;
- pass back the first stitch, moving the needle from left to right;
- throw the first stitch off of the knit needle.
Undo the scrap rows. You certainly know that when undoing the first rows in a knitted piece, the yarn is caught in the first and last stitches. You have to pull it out if you want to recycle the scrap yarn (I always try to do it), or cut it if you want to trow it away.
Now you have a perfectly finished and stretchy edge :)