The most common way to join seams is the mattress stitch, which creates an invisible seam by pulling yarn through the loops on the edges of your pieces
Mattress stitch works by threading a tapestry needle under the horizontal bars between stitches on one piece, then under the corresponding bars on the other piece, pulling the yarn snug every few rows. The seam closes from the inside out, so it stays hidden once you weave in the ends. This method works best on stockinette stitch and creates a seam that's nearly invisible from the outside.
To start, lay your two pieces flat with the right sides facing up. Thread a tapestry needle with a length of yarn (about 18 inches to start). Insert the needle under the first horizontal bar on one piece, between the first and second stitches from the edge. Pull the yarn through, leaving a short tail. Move to the other piece and insert under the corresponding bar, then pull through. Go back to the first piece and insert under the next bar down, then alternate between pieces, pulling the yarn snug every two or three rows so the edges draw together.
Key Takeaways
- Mattress stitch creates an invisible seam by threading yarn under the horizontal bars between stitches on each piece, working from the inside out.
- Backstitch seams are stronger and work on any stitch pattern, but they create a visible ridge on the inside and take up more width than mattress stitch.
- Grafting (Kitchener stitch) joins two live edges without a visible seam line, but requires both pieces to have stitches still on the needle.
- Whip stitch works for joining cast-on or bind-off edges and is the fastest method, though it's less flexible than mattress stitch.
Backstitch seams for durability and any stitch pattern
Backstitch is the strongest seam method and works on any knit pattern, including garter stitch, ribbing, and textured stitches where mattress stitch won't work. The trade-off is that it creates a visible ridge on the inside of your garment and uses up about half a stitch width on each side, so your finished piece will be slightly smaller than if you'd used mattress stitch.
To backstitch, place your pieces with right sides together. Thread a tapestry needle and insert it through both layers one stitch in from the edge. Bring the needle back out one stitch forward, then insert it back into the hole where you just came out, creating a short overlap. Move forward one stitch and repeat. Keep your stitches small and even, and pull the yarn snug enough that the seam holds but not so tight that it puckers the fabric.
Backstitch is especially useful for seaming pieces that will take stress, like the underarms of a sweater or the sides of a bag. It's also the best choice when your pieces are made from different stitch patterns and you need a seam that works everywhere.
Grafting with Kitchener stitch for seamless joins
Grafting (also called Kitchener stitch) joins two pieces of live stitches—stitches still on the needle—without creating a seam line at all. The result looks like a continuous column of stockinette stitch running across the join. This method is most common for closing the toe of a sock or joining the front and back of a sweater at the shoulders, but it only works when both pieces have stitches still on the needle.
To graft, hold the two needles parallel with the right sides of the fabric facing you. Thread a tapestry needle with yarn about four times the width of the seam. The pattern alternates: insert through the first stitch on the front needle from right to left, then through the first stitch on the back needle from left to right, then back to the front needle from left to right (and slip that stitch off), then to the back needle from right to left (and slip that stitch off). Repeat this four-step pattern across, pulling the yarn snug every few stitches so the join stays even.
Grafting takes practice to get smooth, but once you're comfortable with the rhythm, it's faster than it looks. The seam is nearly invisible and has the same stretch as the rest of your fabric.
Whip stitch for cast-on and bind-off edges
Whip stitch joins two finished edges—usually a cast-on edge to a bind-off edge, or two bind-off edges—by wrapping yarn around the edge loops. It's the fastest seaming method and works well for joining the sides of a blanket or closing the opening on a stuffed toy.
Place your pieces with right sides together or right sides facing out, depending on whether you want the seam hidden or visible. Thread a tapestry needle and insert it through the first loop on one edge, then through the corresponding loop on the other edge. Wrap the yarn around the edge of both pieces and insert back through the next loop on the first piece, then the next loop on the second piece. Keep the wraps close together and pull snug every few stitches.
Whip stitch creates a slightly thicker seam than mattress stitch because the yarn wraps around the edges rather than running between them. It's less flexible than other methods, so it's best used on edges that won't need to stretch much.
Choosing the right seam for your project
The best seam method depends on your stitch pattern, how much stress the seam will take, and whether you want the seam visible or hidden. Mattress stitch is the default for most projects because it's invisible and works on stockinette. Backstitch is stronger and works everywhere, but it's visible on the inside. Grafting is seamless but requires live stitches. Whip stitch is fastest for edge-to-edge joins.
If you're seaming a garment that will be worn and washed, mattress stitch or backstitch are your best choices. If you're joining pieces that won't move much—like a blanket border or a decorative seam you want visible—whip stitch is fine. If you're closing a sock toe or shoulder seam and you have live stitches, grafting gives the best result.
Common mistakes and how to avoid them
The most common mistake is pulling the seaming yarn too tight, which makes the seam pucker and reduces the stretch of your fabric. Pull snug enough that the edges hold together, but not so tight that you can see the yarn bunching. Test by gently stretching the seam—it should give a little.
Another mistake is inconsistent tension, which makes the seam wavy. Keep your stitch length and yarn tension the same throughout. If you're seaming a long edge, take a break every few inches, weave in the yarn, and start fresh with a new length rather than trying to seam the whole side with one very long thread.
For mattress stitch, the most common error is going under the wrong bar. Remember: you're looking for the horizontal bar between the first and second stitches from the edge, not the edge stitch itself. If you catch the edge stitch, your seam will be too tight and visible.
Frequently Asked Questions
Can I use regular sewing thread instead of yarn for seaming?
No. Sewing thread is too thin and will break under the stress of a seam that needs to stretch. Always use yarn that matches the weight of your knitting. If you don't have leftover yarn from your project, use a yarn that's the same thickness, even if the color isn't perfect—you can hide the seam inside the garment.
What if I seamed two pieces and the seam is too tight?
You can unravel the seam and redo it with looser tension. Use a seam ripper or small scissors to cut the seaming yarn every few stitches, then pull it out. This doesn't damage the knitted pieces themselves. Reseam with the same method, pulling less tightly this time.
Do I need to block my pieces before seaming?
Blocking before seaming makes the edges even and easier to work with, especially if your pieces have curled or are slightly different sizes. Wet-block or steam-block according to your yarn's care instructions, let the pieces dry completely, then seam. This step isn't required, but it usually results in a neater finished garment.
Can I seam pieces that are different colors?
Yes, but use yarn that matches one of the two colors, or use a neutral color like gray or black. For mattress stitch, the seaming yarn is hidden, so the color matters less. For backstitch or whip stitch, the seam is visible on the inside, so match it to whichever piece will show more.