I decided that I don't like the ridge that slip stitch joining leaves on the back of the afghan. I tried whip-stitching squares together into rows, then joining the rows by whipstitch. I don't like having all those ends to weave. I also tried whipstitching horizontally and then vertically, but the yarn pulls and I get a big gap in the corner joins.
So, today I think I hit upon a new thing that allows you to whipstitch having the LEAST possible ends to weave in. Stairs!
I know you think I've finally succumbed to all the fabric softener fumes, but hear me out...
If you start in the corner and then join a square to two of the adjacent sides, you now have three squares joined like this: (the line represents where you join)
Then, you add the next three stairs by whip-stitching:
X X| X
If you do this, you can have one continuous yarn for each diagonal (as long as you don't run out or it's not too long) and thereby save having to weave in all the ends, you don't get that big gap at the corners, and you DO NOT have that ridge at the back like slip-stitching. Isn't it cool?