*This works best in non-superwash wool. Steeking relies on wool's tendency to stick to itself so with cotton, soft wools and other fibers it's best to test a sample first.
To begin with, knit a pullover sweater. Try on the sweater and place a safety pin, stitch marker or piece of yarn where you want the placket to end. Make sure you measure or count stitches to find the exact center front of the sweater. My example has a cable around the shoulders with 7 plain sts at center front. The central 3 sts will be used to create the placket. If you've never steeked before it's a good idea to try this out on a swatch first.
Baste down the middle of the central stitch with contrasting color sewing thread (I used white), making a horizontal mark at the desired base. With a sewing machine, matching thread, and a very short stitch, sew a straight line half a stitch to one side of your basted line. When you reach the basted bottom, pivot the needle 90º to stitch across the center stitch. Then pivot 90º again and stitch up the sweater half a stitch on the other side of the center stitch. Backstitch at the beginning and end of each stitching line. If your yarn may fray, stitch a second reinforcing line half a stitch away from the first. I reinforced the bottom of the second line of stitching as well.
|Basted with 2 lines of stitching
|...and ready to cut
|The cut slit, stitches secure
Remove the basting thread and you're ready to pick up stitches on either side of the placket, 1½ stitches from center front. The cut edge will fold to the inside and stay nicely out of the way. If you wish, tack down the raw edges with some yarn or thread.
|Picking up placket stitches
I began with the placket overlap, picking up stitches vertically and knitting enough rows to more than cover the 3 stitch gap, then cast off. You can either pick up a few extra stitches along the bottom edge and knit those together with the last knit stitch every other row, or sew the bottom of the overlap band to the sweater. I sampled both methods on a swatch and chose the former. I forgot to take photos at this point I was so excited to be almost finished ;)
To create the underlap I picked up stitches the same way, but 2 fewer sts, then knit the same number of rows and bound off identically. The bottom of the two layers are staggered and create less bulk. The base of the underlap was stitched securely to the sweater.
There you have your henley placket, nicely finished from the outside and stable on the inside. This placket has no buttons or buttonholes but go ahead and add them if you wish. The neckline of my sweater was bound off with 2 st I-cord. I knit 3 rows I-cord per 2 decreased sts and it lies flat on the body (though not in photos).
|Finished placket, pre-steaming