Vertical Seaming Made Easy

Seaming is one of the final—but one of the most important—steps of many projects. It’s also the step that knitters often dread, in part because it’s not knitting, but also because a poor seaming job can ruin the results of an otherwise well-knitted project. In this article, I will explain best practices for using mattress stitch when sewing vertical seams so that your finished projects will look their best from beginning to end.

Plan Ahead

A great seam starts before the knitting process is even complete. Here are a few things you can do while knitting your garment that will make the seaming process easier and give the best result.

Place shaping away from the edge

Keep the edges straight and tidy by moving increases and decreases a stitch or two away from the edge.

Work the selvedge stitch in stockinette

Use one type of stitch at the selvedge, regardless of the stitch pattern that is worked in the rest of the garment. Usually, plain stockinette stitch will result in the smoothest, cleanest selvedge and is perfect for edges that will be seamed. (Exceptions to this are reverse stockinette stitch and k1, p1 ribbing, which will be discussed later.)

Don’t slip the selvedge stitches

Slipping the selvedge stitches can provide a neat finish to an exposed edge but can make seamed edges look a little loose—even sloppy—because each slipped stitch spans two rows. Even if the slipped selvedges are completely hidden in the seam, the adjacent stitches (which will be exposed) may have an uneven tension.

vertical seaming

You’ll use vertical seaming on the Mitte Tee by Sarah Kelliher (knitscene Winter, 2019).

Before You Start to Seam

Once the individual pieces of the garment are complete and you’re ready to sew them together, there are a couple of things you can do before you begin that will help to streamline the seaming process.

Clip the edges together

It’s easy to get so focused on each stitch when you are joining two pieces that you don’t notice that one edge is suddenly much shorter than the other. This happens when you skip running threads on one piece and not the other. The best way to prevent this from happening is to clip the two edges together every 10 rows with locking stitch markers. That way, you will know right away whether the edges are starting to become mismatched. If the two edges do not have the same number of rows, distribute the extra rows evenly among the clipped groupings. For example, if you have 50 rows on one edge and 53 rows on the other, clip the edges together into five sets. The edge with 50 rows will have 10 rows in each set, but the edge with 53 rows will have 11 rows in three sets and 10 rows in the other two sets. As you finish seaming each set that contains an extra row, you will need to catch two running threads, instead of one, on the edge with the extra row.

Select the seaming yarn

In most cases, you can use the project yarn to seam, but if the yarn is too bulky, fragile, or textured, you will have to use a substitute. Choose a smooth yarn that is the same or smaller yarn-weight classification than the project yarn, one of the same or similar fiber, and one that requires the same washing instructions. The color does not have to be an exact match because when the seam is done properly, the yarn will not be visible.

Start at the Bottom

When seaming sweater pieces together, start at the lower ribbed end and work up. This will keep the cuff edges perfectly matched and hide the one-row offset that occurs at the underarm.

Use the cast-on tail to start the seam and then join additional yarn when the tail runs out. If there is no tail attached to either lower corner (or if a yarn other than the project yarn is being used for seaming), join a separate seaming yarn as follows: Thread the yarn onto a tapestry needle and insert the needle up through a stitch at the corner of one of the edges, as shown in Photo 1.

vertical seaming

Then connect the two pieces using a figure-eight join as follows: Insert the tapestry needle up through the space just above the cast-on row on the opposite edge, between the selvedge stitch and the second stitch, pull the yarn through, leaving some slack (Photo 2).

vertical seaming

Next, bring the yarn behind the strand that connects the two edges and insert the tapestry needle up through the space above the cast-on row on the first edge, between the selvedge and second stitch (Photo 3). Gently pull the slack out of the yarn to close the edges.

vertical seaming

You are now ready to start seaming.

Choose the Best Seaming Method

There are a few options for seaming methods, depending on your particular project.

Stockinette selvedges (one full stitch from each edge)

Insert the tapestry needle down through the fabric between the selvedge stitch and the second stitch, then catch the running thread between the stitches (Photo 4). Pull the yarn through, leaving some slack. Repeat this step on the opposite edge. Always insert the tapestry needle down through the same space where the yarn came up previously.

vertical seaming

Every 3 or 4 repeats, pull slack out of the seaming yarn until the edges meet (Photo 5). Do not pull too tightly, because doing so will make the seam too rigid. Leave slack in the last stitch so that you can see where to insert the needle for the next stitch.

vertical seaming

As you approach the locking stitch marker, count the number of remaining running threads to catch on each edge. If the number is unequal, catch one thread on the shorter edge, as usual, but catch two running threads on the longer edge.

Photo 6 shows that the stitch pattern continuity is maintained across the seam line. An entire stitch from each edge will end up on the wrong side of the work.

vertical seaming

Stockinette selvedges (half stitch from each edge)

This seam is a good option when you are using a bulky yarn and want to reduce the thickness of the seam, because only half a stitch from each edge will end up in the seam (although it can be trickier to get this seam to look neat if your selvedges aren’t even).

For this seam, bring the tapestry needle down through the center of the selvedge stitch and then up through the center of the selvedge stitch above (Photo 7).

vertical seaming

Because of the structure of selvedge stitches, you will catch the head of the stitch on one row, and then the next time, you will catch the bump formed by the twisted stitch on the following row (Photo 8).

vertical seaming

Photo 9 shows how each edge forms one half of the V of the stitch, maintaining continuity across the seam line.

vertical seaming

Reverse stockinette selvedges

When seaming edges of reverse stockinette fabric, keep the selvedges in reverse stockinette, too.

For each row of reverse stockinette fabric, there is a set of offset bumps. The upper set of bumps (sometimes referred to as “frowns”) are the heads of stitches (Figure 1), while the lower bumps (known as “smiles”) are the running threads between stitches (Figure 2).

vertical seaming

vertical seaming

To maintain the continuity of the stitch pattern across the seam line, catch a lower bump on the left edge (Photo 10) and an upper bump on the right edge (Photo 11). This will take a full stitch from the left edge and a half stitch from the right. Find the upper bump on the right edge by locating the lower bump nearest to the selvedge, then look to the left. Photo 11 shows the perfect continuity of the reverse stockinette pattern across the seam line.

vertical seaming

Selvedges for ribbing

In order to maintain the continuity of a rib pattern across a seam, it is necessary to plan ahead and begin and end the rib pattern accordingly. The k2, p2 rib shown in Photo 6 was worked over a multiple of four stitches, plus two, starting and ending the right side of each piece with k2. Because a full stitch from each piece was hidden on the wrong side of the work, only two stitches remained visible at the seam. When working a full-stitch seam for your project, work k1, p1 rib over an even number of stitches. When seaming, capture the running thread between the first and second stitches to eliminate a full stitch at each edge and maintain the rib pattern across the seam, as shown in Photo 9. The stockinette portion of Photo 9 is shown with a half-stitch seam. If you would like the k1, p1 rib to also have a half-stitch seam, work the rib pattern over an odd number of stitches, starting and ending right-side rows with k1.

Having a plan for your seams before you cast on will ensure that your finished project will look as beautiful as possible.


Roxanne Richardson is a certified master handknitter who lives, designs, and teaches in Minneapolis, Minnesota. Find her weekly videos on YouTube.

This article originally appeared in knitscene Winter 2019.


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