There are many different seaming techniques that you can use. However, for joining the sides of two Stockinette Stitch pieces together, we recommend using the Mattress Stitch.
The Mattress Stitch creates a vertical seam that is invisible. In fact, it makes the knitting appear continuous even though you have knitted the pieces flat.
To make it easier to sew the two pieces together, we recommend that you block your pieces first. This will make the edges smoother and easier to seam.
In addition, we recommend that you use your knitting yarn to sew the pieces together. However, if you have used a yarn that is not very strong, like mohair, a novelty yarn, etc. this yarn may not be suitable for seaming.
In this case, use a smooth, firm yarn that is in a compatible color. It does not have to be an exact match as, remember, the seam will be virtually invisible.
On the other hand, if you have left a long tail from your cast-on row, you can use this strand to begin seaming.
In the drawings below, we have used a contrast color for illustration purposes only.
Step-By-Step Mattress Stitch Knitting Tutorial
Make sure that the right sides of both knitted pieces are facing you.
Method 1: Using the Yarn Tail
Thread the needle and insert it from back to front into the corner stitch of the piece without the yarn tail.
Method 2: NOT Using the Yarn Tail
Start by weaving in the yarn tail so it does not get in the way. Then thread the needle with the yarn you are going to use for sewing. Pick one corner (we suggest the one on the right-hand side). In the corner, insert the needle from back to front.
Making a figure eight with the yarn, insert the needle from back to front into the corner stitch of the opposite piece. Tighten to close the gap.
To continue seaming, insert the yarn needle under the first horizontal bar/strand on the right-hand piece. Make sure that you use the bar/strand that is between the edge stitch and the adjoining stitch.
Insert the yarn needle under the corresponding bar/strand on the other piece.
To make a firm, strong seam, continue alternating from side to side, making sure you sew under each bar/strand on both sides.
Make sure to pull the yarn tight every inch or so. If you are a metric user, that is about every 2.5 cm. You should ensure that the yarn is tight enough to draw the two edges together. However, it should be loose enough for the seam to still stretch a little.
Once the seam is completed, weave in the end(s).
Enjoyed this tutorial? Why not check out our other tutorial on how to join yarns when knitting?