How to Kitchener (graft) garter stitch
Kitchener stitch, or grafting, enables you to join two pieces of knitting without leaving a visible seam. (Fun fact: it's named for the British military leader Lord Kitchener, who promoted it as a way to avoid the toe chafing his soldiers suffered from with seamed socks. File with raglan and cardigan as knitterly terms with surprising military origins.)
The concept is simple, though a little fiddly: you're just drawing a length of yarn through stitches from each piece in turn so as to create a row of perfectly formed "knitted" stitches. It's most often used on straight stocking stitch edges, but can easily be varied for other circumstances. In Nullkommanix, it's done in garter stitch – and one edge to be joined is a mock provisional cast-on, rather than true live stitches. The end result is almost perfect… but not quite as invisible as it would be if worked on live stitches. That's absolutely fine when using a funky, thick-and-thin, multi-coloured yarn – you really can't tell. If you're using a smooth yarn as in the tutorial, in choosing between a true and mock provisional cast-on, you'll have to decide on your own levels of perfectionism.
How it's done
You need the two pieces to be joined to have opposite presentations – with the top row on one side showing as knit, one as purl. If this is a single folded piece (for instance, joining a length of garter stitch to make a tube), that means working an odd number of rows.
1. Hold the two pieces together, needles pointing right and purl ridge on the front needle. If your yarn is attached to the front needle (as shown), start by drawing yarn needle through the first stitch on the back nedle, to anchor it.
2. Insert needle purlwise (ie, pointing towards you) into first stitch on front needle and draw through.
3. Insert needle knitwise (pointing away) into stitch on the back needle. Note: in later repeats this will mean working back into the same stitch as previously worked, which is shown here.
4. Drop stitch off needle and insert stitch purlwise into next stitch on back needle.
5. Insert stitch knitwise into the same stitch as previously worked on front needle and drop it off.
Repeat steps 2-4 until all stitches have been grafted.
The finished graft, before and after taking up slack.