Here is one way to join two pieces together using the slip stitch on the outside loops, whether it is pieces of a garment, granny squares, or anything else that needs to be joined together with a seam. This one is one of my favorite ways because it produces an invisible seam on the "right" side and because it works the outside loops, it makes your pieces look like they are sitting side by side. Plus, you don't even have to put your crochet hook down and it is super fast...always a bonus!
I'll be showing you how to join two ends of a green scarf using purple yarn to make everything stand out. Normally I would use the same color, but this will make it easier to see.
Begin by facing the "right" side of both pieces inward so that the "wrong" sides are facing out. If you just finished your piece instead of snipping the yarn, just keep going. Otherwise secure another piece of yarn to the end.
Next, insert the hook into the outside loops of both pieces,
Wrap yarn around hook,
and pull through both loops. Now we can begin working across.
Next, insert the hook into the next two outside loops and wrap yarn around hook.
Pull through the first two loops (the green ones in this case). It should now look like the photo below:
Now pull that loop through the other loop.
There should be one loop left on the hook. Keep repeating all the way across...
until you reach the end. Fasten off and weave ends if needed.
Here is what the seam will look like on the "wrong" side,
And here it is on the outside, or "right side" I love how it disappears, even with the contrasting yarn.