You can mattress the edge stitches together, but if you want to mattress the garter stitches, you pick up the bottom loop on one side and the top loop of the other side (of the purl ridges) and can mattress stitch that way. It makes a nice invisible seam, too.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry