Sewing seams might feel like a skill that's unnecessary to knitting, but with some clear instructions, and a little practice, all kinds of designs will become accessible to you! Nearly all of my knitting designs are knit flat, and this means they require seams to become 3-dimensional toys or garments. My Snow Day outfit uses three different kinds of seams, all on just the parka. So if you'd like to take your knitting even farther, follow along to see how I manage these three kinds of seams.
To sew any seam, you'll need a blunt tapestry or darning needle, and some yarn. For this tutorial, I'm demonstrating the stitches with a contrasting length of yarn, so you can more clearly see what I've done. Normally, you would use yarn matching your knitted piece. I like to leave long ends when casting-on and binding-off, as these are convenient to use for sewing seams.
All of the seaming types I show here are done from the right-side of the knitted fabric, which allows you to make sure the seam looks good on the visible side. Please note that all these examples are done on stockinette, because that's what most of my designs use. If you need help sewing seams on other stitch patterns, a quick internet search should be helpful.
When sewing seams, it's very helpful to be able to find the columns of stitches which make up stockinette. These are the lines or stacks of v's you see on the right side. Make sure to examine your knitting to identify these columns, before sewing a seam.
Seam Type 1: Vertical-to-Vertical Seam (mattress stitch)
This kind of seam joins two vertical edges of knit fabric. These vertical edges may be from two separate pieces, such as the front and back of a sweater, or they can be the vertical edges of a piece that you curve around to form a tube- or ball-shape, such as the body or head of a toy. Here I'm joining two separate pieces, because it's easier to show the seam clearly.
The method used to join two vertical edges is called "mattress stitch." Basically, you're sewing back and forth between columns of stitches along the two edges, in a way that brings the pieces together in an almost invisible seam. Your sewing will bring together the second column of stitches along each edge, with the first column hidden on the WS as the selvage.
In the photo below, I've started at one end of the edge of one piece. I'm threading the sewing yarn through from the wrong-side (WS) of the fabric, coming up between the first and second columns of stitches. From the right-side (RS), I make a vertical stitch along the side of the second column of stitches of the opposite piece, running the needle behind the "bars" joining the columns of stitches. These bars are what you see as purl bumps on the WS of the fabric. I run my needle behind two "bars" for each stitch.
The reason I run my needle behind two bars for each stitch is because it makes the vertical seam resemble a line of knit stitches. I find this method makes a tidy, sturdy seam that's not too bulky. Below I've left the stitches loose, so you can see how the sewing yarn moves back and forth between the two vertical edges. Each stitch on each side is made through the two bars above the ones I used in the previous stitch on that side.
In the photo below, I've tightened up all the stitches made by the sewing yarn. This pulls the two vertical edges next to each other, so the columns of stitches are aligned as if it's one piece of stockinette fabric. Just make sure you don't pull too tight, and pucker the fabric. As you can see, even though I'm using a contrasting colour to sew the seam, it's very hard to see on the RS of the fabric!
This photo shows the seam from the wrong side, with the selvages pushed to one side so you can see the stitches holding the two pieces together.
This photo shows how the WS of the seam usually looks, with the selvages snuggled up next to each other in a tidy fashion.
Here is the vertical seam, sewn all the way to the top. I like to make a small stitch to loop the bound-off edges together, if this will show on the finished object. This kind of seam can give your knitted project a lot of strength and stability in areas which take extra stress, and it barely shows, once you've learned how to accomplish it neatly.
Seam Type 2: Horizontal to Horizontal Seam
This kind of seam joins two horizontal edges of knit fabric together. These can be bound-off or cast-on edges, or one of each. The photos below show two bound-off edges being joined, because that's what you'll usually encounter in my knitting patterns. This seam type resembles grafting or duplicate stitch, and I've occasionally referred to it in both ways in my patterns. I can't find that it has it's own name like mattress stitch. (If you know of one, I'm happy to update this post with that info!)
Like with mattress stitch, I've started on one end of the edge of one piece. I've threaded the sewing yarn through from the WS of the fabric, coming up between the first and second columns of stitches. On the RS, I've run the needle and yarn under the first stitch of the first column of the opposite piece. Next, I run the needle under the first stitch of the second column on the starting piece.
As you continue along the edge, making stitches between both sides, you will see that the line you are sewing resembles a row of knit stitches. Make sure to match your tension to that of your knitted fabric. The columns of stitches of each piece appear to flow into each other, making the two pieces look like a single piece of stockinette fabric.
On the WS of your work, you can see that the bound off edges are pulled together and towards the WS. The line of stitches you're sewing snuggles between the purl bumps, and is barely visible, even in a contrasting yarn.
When a horizontal to horizontal seam is sewn with matching yarn, and your tension is the same as your knitting, it's nearly invisible. Unlike grafting (that is, sewing live stitches to live stitches), this seam will not stretch, providing a stable base for stress on your knitted object.
Seam Type 3: Vertical to Horizontal Seam
This kind of seam joins a vertical edge to a horizontal edge. This is not a method I use a lot in my designs, but it can be a little tricky, so I wanted to demonstrate it as well. One reason this seam can be trickier is because you're essentially using both of the techniques described above, one on the vertical edge, and the other on the horizontal edge.
The other reason this seam can be a bit more difficult is because knit stitches are wider than they are tall. This means that for a certain distance, you need to work more rows than stitches. You can see this in any gauge given for stockinette stitch. In the two kinds of seams shown above, you should always be matching the same number of rows or stitches on each side of the seam. For a vertical to horizontal seam, however, you will have more rows on one side, than there are stitches on the other. (For example, these swatches are 15 sts by 17 rows).
I've started on one end of the seam of the vertical piece, threading the sewing yarn through from the WS of the fabric, coming up between the first and second columns of stitches. On the RS, I run the needle and yarn under the first stitch of the first column of the opposite piece. As you can see, this stitch is just like the first stitch on a horizontal to horizontal seam. Next, I run my needle under two bars between the first and second columns of stitches, on the starting side. This is just like mattress stitch.
In order to even out the difference between stitch and row count between your two edges, you will occasionally have to run your needle under only one bar on the vertical edge. If you keep the two edges lined up with each other, you should see when this is necessary (it depends on your gauge, so there's no firm rule on how often it will be necessary). If you do find that the two sides are becoming uneven, pull out a few stitches and try again. It's worth a little extra time to make sure the seam is even and tidy.
In the photo above, I've left my stitches loose so you can see them better. Below, you can see how the seam will look with the stitches pulled tighter. This will bring the two edges firmly against each other, and pull the selvages to the WS.
In the photo below, I've sewn the seam with matching yarn, and you can see how neatly the two edges match up.
Below is the vertical to horizontal seam from the WS, sewn with matching yarn.
The hooded coat/parka from my Snow Day outfit uses all three of these seam types. While it may seem like a lot of work, the finished garment is very satisfying and adorable, and sure to stand up to a lot of playing!
The front and back are attached with vertical to vertical seams at each side. I also used this method to sew the sides of the patch pockets.
The top of the shoulders are joined with a horizontal to horizontal seam. It's rather hard to see on the finished parka, so I've placed the tapestry needle to point at the seam. In the photo above, you can also see the seam along the bottom of the patch pockets, where I've used a version of this seam type. (I also use this seam type for the feet of my bunnies and kangaroos).
The hood has two vertical to horizontal seams, attaching the top flap to the sides of the hood. This gives the hood width and depth, so it fits nicely around the head of a toy.
I hope you find this tutorial useful. I may update or adjust the wording at some point, if I finds it needs additional clarification.