For the mattress stitch, sew two knitted pieces together by grabbing one strand of thread from each edge, alternating back and forth, working vertically along the edges. The strand of yarn you take is a horizontal bar that extends between the knitting points (or “V”). The secret of the mattress stitch is to keep the seam elastic without allowing it to stretch too much. The best way to do this is to work very loosely a few centimeters and then pull the sewing thread so that the stitches come together.
Pull the seam slightly from the top and bottom to add a little stretch. This step starts the stitch pattern of your mattress. Start by placing two pieces of tissue next to each other, with the right sides facing up. Measure a length of thread that is at least three times the length of the desired seam.
Thread it with a tapestry needle. Be sure to work on the first bar above the plaster edge, slide the needle tip through the bar between the first and second point. If you're wondering how to sew your knit stitches together, then you've come to the right place. In this Berroco Knit Bits video tutorial, you will learn how to join two pieces of knit together in jersey stitch.
This is done by stitching through a bar between the stitches on one side of a knitted piece and then a corresponding bar on the opposite side of the other knitted piece. Just use the same principles as for sewing the inverted sock stitch by stitching the upper bars on one side of the seam and the lower bars on the other. Go back to the opposite side and, working in two rows, repeat this process in a zigzag, always taking the needle under the threads that exactly correspond to the other side and entering the hole from which the last stitch came out of that side, taking care not to lose any row. Simply find the point where you need to unhook and slide the tip of the needle under the stitch at that point and pull the working thread gently until all the stitches on the mattress above that point are undone.
You can see that the stitches immediately to the left of the seam are in the same direction as those on the right of the seam instead of mirroring them, so it looks like the middle row of stitches has two left arms. In the image below you can see that I have numbered the 3 columns of stitches closest to the edge of the work. These “bars” between stitches are what you want to sew when working the mattress stitch, commonly referred to as a “channel between stitches” and the best channel to use is the one between stitch 1 (which is right on the edge of the work) and stitch 2, as shown here. This is a little more complicated, but only because on one side of the seam you want to sew the top of one stitch, and on the opposite side you will have to sew the bottom.
This video shows how to knit the mattress seam into a sock stitch by working through the center of the edge stitch, another option for vertical seams. Instead, I ignore the bars in alternate “soft” rows and just sew stitches into the “bumpy” rows. When joining garter stitch, work in the center of the first stitch of the row instead of between the first and second stitches. Personally, I am a lover of seams, especially mattress stitch because it gives a very professional finish, so I thought I would write a little bit about the benefits of using a mattress stitch seam and the best way to work it on different knitted surfaces.
When joining two ribbed sections, work in the center of the first stitch of the row instead of between the first and second stitches.