The Three Main Seaming Methods for Knitted Fabric
The seam you choose depends on which edges you're joining and what look you want. Mattress stitch creates an invisible seam and works best on stockinette stitch pieces where you have live stitches or a selvage edge. Backstitch is the strongest option and works on any stitch pattern, but it creates a visible line and uses up a small amount of fabric. Grafting (also called Kitchener stitch) joins two sets of live stitches with no seam at all—the new row looks like it was knitted as part of the original fabric.
Most sweaters and garments use mattress stitch on the sides and backstitch on shoulders, because mattress stitch is nearly invisible and backstitch holds up to the stress of a shoulder seam. If you're joining pieces that both have live stitches still on the needle—like when you're adding sleeves—grafting is the right choice.
Key Takeaways
- Mattress stitch creates an invisible seam by working into the horizontal bars between stitches on the edge of your knitted piece.
- Backstitch is the strongest seam and works on any edge, but it creates a visible line and requires you to work one stitch in from the edge.
- Grafting joins two sets of live stitches so the seam looks like a knitted row, with no visible seam line at all.
- Thread a tapestry needle with yarn the same color as your knitting, and always work on the wrong side of the fabric unless you're grafting.
- Tension matters: pull your seaming yarn snug enough that the seam holds, but not so tight that it puckers or draws the fabric in.
Mattress Stitch: The Invisible Seam
Mattress stitch works by catching the horizontal bars of yarn that run between your edge stitch and the next stitch over. Lay your two pieces flat on a table with the right sides facing up and the edges you want to join side by side, about half an inch apart. Thread a tapestry needle with a length of yarn about 18 inches long—you can always thread more if you run out.
Start by bringing your needle up through the bottom of the left piece, one stitch in from the edge. Go across to the right piece and bring the needle up through the bottom edge, one stitch in from the edge on that side. Now you're ready to begin the actual seaming. Bring your needle up under the first horizontal bar on the left piece (the bar that sits between your edge stitch and the next stitch), then cross over and go under the first horizontal bar on the right piece. Come back to the left piece and go under the next bar up, then back to the right piece and under the next bar up. Keep going in this zigzag pattern, working under one bar on each side, moving up the seam.
Every few inches, gently pull your seaming yarn to close the gap between the two pieces. The edges will fold toward the wrong side and the seam will disappear. Don't pull too hard—if the seam puckers or the fabric bunches, you've tightened it too much. The goal is a flat, invisible line.
Backstitch: The Strongest Seam
Backstitch creates a sturdy seam that can handle stress, making it the right choice for shoulder seams or any place where the knitting will take weight. Place your two pieces with right sides together and pin them if you want to keep them from shifting. Thread your tapestry needle with yarn.
Bring your needle up through both layers one stitch in from the edge of the left piece. Go back down one stitch to the left, then come back up one stitch to the right of where you started. You've now made one backstitch. Repeat this motion—going back one stitch, then forward one stitch—all the way up the seam. Each new stitch should overlap slightly with the one before it, creating a solid line.
Work slowly and keep your stitches small and even. A backstitch seam is only as strong as the tension you maintain, so pull your yarn snug after every few stitches. When you're done, the seam will be visible on the wrong side as a solid line of yarn. If you're seaming a visible edge (like the top of a ribbed cuff), you can work backstitch on the right side, but it will show as a line of yarn running along the edge.
Grafting: Joining Live Stitches
Grafting works only when both pieces have live stitches on the needle—usually when you're attaching a sleeve cap to an armhole or joining two pieces that were knitted toward each other. Arrange the two needles so the stitches face each other, with the right sides of the fabric facing out. Thread a tapestry needle with a length of yarn about 24 inches long.
Bring your needle through the first stitch on the front needle from right to left (as if to purl), then through the first stitch on the back needle from left to right (as if to knit). Now go back to the front needle: insert your needle through the same stitch you just came out of, from right to left, then through the next stitch to the right, from left to right. Move to the back needle: go through the same stitch you just came out of from left to right, then through the next stitch to the right from right to left. Keep repeating this pattern—front needle (same stitch, then next stitch), back needle (same stitch, then next stitch)—all the way across.
The rhythm is: front through, back through, front through, back through. Every few stitches, gently pull your yarn to snug up the seam. When you've grafted all the stitches, the seam will look like a row of knitting, with no visible seam line at all. This takes practice—your first grafted seam may look uneven, but the tension evens out once you wear the garment.
Preparing Your Pieces and Yarn
Before you seam, make sure your pieces are blocked to the right dimensions. Blocking sets the stitches in place and makes edges even, which means your seams will be straighter and your finished garment will fit better. Wet-block by pinning your pieces to shape on a blocking board, spraying them with water, and letting them dry. Steam-blocking works too if you have a steamer and are careful not to flatten the texture of your knitting.
Use yarn the same color as your knitting for the seam. If you don't have leftover yarn from your project, match the color as closely as you can—a slightly lighter shade is less noticeable than a darker one. Cut a length of seaming yarn about 18 to 24 inches long and thread it onto a tapestry needle (also called a yarn needle). A tapestry needle has a blunt tip and a large eye, so it won't split your yarn or poke holes in your stitches the way a sharp needle would.
Common Mistakes and How to Fix Them
The most common mistake is pulling your seaming yarn too tight. This draws the fabric in, creates puckers, and makes the seam visible even when you're using mattress stitch. If you notice this happening, undo the last few inches of seaming, loosen your tension, and try again. A good seam should feel snug but not tight.
Another mistake is working into the wrong part of the stitch. In mattress stitch, you need to catch the horizontal bars between stitches, not the stitches themselves. If your seam looks bumpy or thick, you may be going through the stitch loops instead of under the bars. Look at your edge closely and identify where the bars are—they run horizontally between the vertical stitch columns.
Uneven tension is also common, especially when you're learning. If some parts of your seam are tight and others are loose, the seam will look wavy. The fix is to go slowly, pull your yarn with the same pressure every time, and check your work every few inches. If a section looks uneven, undo it and redo it before moving on.
Seaming Different Stitch Patterns
Mattress stitch works beautifully on stockinette stitch because the horizontal bars are clear and straightforward to see. On ribbed fabric, the bars are still there but they're smaller and less obvious. Work mattress stitch the same way, but look more carefully for the bars and work into them slowly.
Garter stitch (knit every row) has bumps instead of smooth horizontal bars, so mattress stitch is harder to work and the seam may be slightly visible. Backstitch is often a better choice for garter stitch pieces. Textured stitches like cables or seed stitch also work better with backstitch, because the texture makes it hard to find and work into the horizontal bars.
If you're seaming pieces in different stitch patterns—like attaching a stockinette body to a ribbed cuff—use the method that works best for the stitch pattern of the main piece. The seam will be less visible if it blends with the dominant texture.
Frequently Asked Questions
Can I use the same yarn I knitted with for seaming?
Yes, if you have leftover yarn. Cut a length from your ball or use the tail you left when you cast on or bound off. The same yarn will match perfectly and blend into your seam. If you don't have enough, use yarn as close in color as possible.
What if my seam is too tight and puckers the fabric?
Undo the seaming back to where it looks good, then redo it with looser tension. Pull your seaming yarn only hard enough to close the gap between the two pieces—it should feel snug but not tight. If you're having trouble controlling tension, try using a slightly thinner yarn for seaming, or practice on a swatch first.
Do I have to block my pieces before seaming?
Blocking makes seaming much easier because it evens out your edges and sets the stitches in place. If you skip blocking, your seams may be uneven or wavy. At minimum, wet your pieces lightly, pin them to shape, and let them dry before you seam.
Can I seam with a regular sewing needle?
A regular sewing needle will split your yarn and create holes in your stitches. Use a tapestry needle, which has a blunt tip and a large eye designed for yarn. They cost a few dollars and last for years.
What's the difference between mattress stitch and grafting?
Mattress stitch joins two finished edges (edges that have been bound off). Grafting joins two sets of live stitches (stitches still on the needle). Grafting creates a seam that looks like a knitted row, while mattress stitch creates an invisible seam between two edges. Use grafting when both pieces have live stitches, and mattress stitch when the edges are bound off.