What seaming does and which method to use

Seaming joins two pieces of knitting together after you've finished knitting them separately. The seam itself is made with a needle and yarn, not with your knitting needles. The method you choose depends on which edges you're joining — whether they're live stitches still on the needle, cast-off edges, or the sides of your pieces — and what kind of seam you want the finished garment to show.

The three most common seaming methods are the mattress stitch (which creates an invisible seam on the right side of stockinette stitch), the backstitch (which is strong and visible, used mostly on edges where a seam line is expected), and the Kitchener stitch or grafting (which joins two sets of live stitches so there's no seam line at all). Each one requires a different technique and works best in different situations.

Key Takeaways

  • Mattress stitch creates an invisible seam on stockinette stitch by picking up the horizontal bars between stitches on each side, and is the standard choice for joining sleeves to bodies and side seams.
  • Backstitch is a visible, durable seam worked through the bumps at the edge of your knitting, best used on ribbing, garter stitch, or anywhere a seam line won't show.
  • Kitchener stitch (grafting) joins two rows of live stitches without creating a seam line, and requires both edges to have the same number of stitches.
  • Use yarn the same weight as your project yarn, threaded on a tapestry needle with a blunt tip, to avoid splitting your stitches.
  • Practice on a swatch first so you can see how each stitch looks and feel the tension before seaming your finished pieces.

Mattress stitch for invisible seams on stockinette

Mattress stitch is the most common seaming method because it's nearly invisible on the right side of stockinette stitch. You work it from the right side of the fabric, picking up the horizontal bars that run between the columns of stitches on each edge. The seam itself sits inside the fabric, hidden from view.

To work mattress stitch, lay your two pieces flat with the right sides facing you. Thread your tapestry needle with a length of yarn about 18 to 24 inches. Insert the needle under the horizontal bar between the first and second stitch on one piece, then go across to the other piece and insert under the same bar on that side. Come back to the first piece and go under the next bar up, then back to the second piece. Continue this zigzag pattern, picking up one bar on each side in turn. After every few stitches, pull the yarn snug so the edges draw together and the seam disappears into the fabric.

Mattress stitch works best on stockinette stitch because the horizontal bars are clear and straightforward to see. It's less effective on textured stitches like garter stitch or ribbing, where the bars are less distinct. If you're joining pieces that have different stitch counts on each side, you can adjust by picking up two bars on the wider side and one on the narrower side to keep the seam straight.

Backstitch for durable seams on ribbing and textured stitches

Backstitch creates a visible seam line and is much stronger than mattress stitch, making it the right choice for ribbing, garter stitch, or any edge where you expect to see a seam. You work it from the wrong side of the fabric, sewing through the bumps at the very edge of your knitting.

Lay your pieces with wrong sides together. Insert your needle through the bump of the first stitch on one piece, then through the corresponding bump on the other piece. Bring the needle back out one stitch ahead on the first piece, then go back through the same bump you just came out of on the other piece, and forward one stitch. This creates overlapping stitches that lock the pieces together. Keep your tension even so the seam doesn't pucker, and work close to the edge so the seam sits neatly.

Backstitch is also the method to use when you're joining a cast-off edge to a side edge, or anywhere the edges are not the same type. Because you're working through the bumps rather than between stitches, you have more control over where the seam sits and can adjust for differences in row gauge or stitch count more easily than with mattress stitch.

Kitchener stitch for seamless joins of live stitches

Kitchener stitch, also called grafting, joins two rows of live stitches (stitches still on the needle) so that the join looks like a continuous row of knitting with no seam line. This is the method used to close the toe of a sock or join the two halves of a sweater body without a visible seam.

Both edges must have exactly the same number of stitches. Hold the two needles parallel with the right sides of the fabric facing you. Thread your tapestry needle with a length of yarn about 24 inches. Insert the needle through the first stitch on the front needle as if to purl, then through the first stitch on the back needle as if to knit. Go back through the first stitch on the front needle as if to knit and slip it off the needle. Go through the next stitch on the front needle as if to purl. Then go through the first stitch on the back needle as if to purl and slip it off. Go through the next stitch on the back needle as if to knit. Repeat this pattern — purl on front, knit on back, then knit on front, purl on back — until all stitches are grafted.

The rhythm takes practice, but once you understand the pattern (purl, knit, knit, purl, repeat), it becomes automatic. Work slowly and keep even tension so the grafted stitches match the size of the stitches in your knitting. If you pull too tight, the join will pucker; if you pull too loose, it will be floppy.

Choosing the right yarn and needle for seaming

Use yarn the same weight as the yarn you knitted with. If you used a variegated or multicolored yarn, a solid color that matches the predominant color usually blends better than trying to match the exact variegation. If you don't have leftover yarn from your project, save a length before you cut the yarn at the end of knitting.

A tapestry needle with a blunt tip is essential. The blunt tip slides between stitches without splitting the yarn fibers, which would weaken the seam and make it look rough. Tapestry needles come in different sizes; choose one that's large enough that the yarn threads easily but not so large that it leaves visible holes in your fabric. For most worsted-weight yarn, a size 16 or 18 tapestry needle works well.

Seaming practice and common mistakes

Before seaming your finished pieces, practice on a swatch. Knit two small rectangles in the same stitch and yarn you used for your project, then practice each seaming method on them. This lets you see how the seam looks, feel the right tension, and understand the rhythm of each stitch without the pressure of seaming your actual garment.

The most common mistake is pulling the seaming yarn too tight. This makes the seam pucker and distorts the shape of your pieces. Pull just snug enough that the edges come together; the yarn should disappear into the fabric, not cinch it. Another mistake is using yarn that's too thick or a needle that's too large, which creates visible holes along the seam line. If you're seaming a delicate yarn, you may need to use a thinner yarn for the seam itself, or split your project yarn into thinner strands.

If you notice your seam is uneven or crooked as you work, you can usually fix it by adjusting which bars or bumps you pick up on the next few stitches. Seaming is forgiving enough that small corrections won't show in the finished garment.

Frequently Asked Questions

Can I use the same yarn for seaming that I used for knitting?

Yes, use the same weight and fiber. If you don't have leftover yarn, save a length before you finish knitting. For a variegated yarn, a solid color that matches one of the colors in the variegation usually blends better than trying to match the exact pattern.

What if my two pieces have different numbers of stitches on the edges?

With mattress stitch, you can pick up two bars on the wider side and one on the narrower side to compensate. With backstitch, adjust by occasionally picking up two bumps on one side and one on the other. Kitchener stitch requires both edges to have exactly the same number of stitches, so you may need to pick up stitches or bind off differently on one piece.

How do I fix a seam that's too tight or puckered?

If you notice the problem while seaming, you can rip back a few stitches and redo them with looser tension. If the seam is already finished, you can carefully rip it out with a seam ripper or small scissors and re-seam it. It's worth the time to get the tension right, since a puckered seam will distort the shape of your garment.

Should I block my pieces before or after seaming?

Most knitters block before seaming because it's easier to handle individual pieces and the blocking helps even out the edges so they seam more neatly. However, some prefer to seam first and then block the whole garment. Either way works; choose whichever feels easier for your project.