Would somebody please be kind enough to advise me on how to seam shoulders from a stair-step bind-off in garter stitch. I’ve only seen this done in stocking stitch. Also I am knitting the sweater in stripes in garter stitch, please could you advise how best to seam it making the stripes match up.
You can use mattress stitch on garter fabric, the v of the stitches is still there, maybe a little hidden under the bind off edge.
If you aren’t familiar with mattress stitch there are lots of video tutorials and you can practise on some straight swatches first.
Here is a really nice result on the stair step bind off seam. There are some tutorials which have you seam from one row to the next in half stitches which is a bit ugly in the result but this one explains exactly where to go, behind full stitches, to create a really smooth seam, watch to the end to see it complete then blocked, so professional looking.
I love using mattress stitch to seam sweaters but for stripes, this variation may help with the alignment. It’s demonstrated on side by side stockinette but you’ll have to see if you can adapt it to garter stripes at the shoulder seam.
I haven’t tried this yet as I tend to use a back stitch seam when I need to align stripes.