Remember when you first began to knit, you reached a certain point and realized there were less stitches than what you started with. Unaware, you most likely dropped a stitch or decreased. Learning to decrease is necessary for knitting garments and for many pattern stitches such as lace.
Decreasing reduces the number of stitches, to narrow or shape a piece. For example, decreasing stitches to shape an armhole allows room for sewing in the top of a sleeve. Decreases are also used in combination with increases to make stitch patterns like bobbles. Lace knitting uses decreases to compensate for the yarnovers.
There are a variety of methods to decrease, depending on what you are trying to achieve. All decrease methods pull the stitches on a diagonal to the right or left (slant direction). If decreases are worked randomly or at the very edge of your work, the direction of the slant may not be significant. But it’s important for symmetrical shaping, raglan or V-necks, where a line is visible and becomes a decorative detail. You might want to work a left slant on the right hand side of a piece, and a right slant on the left hand side to emphasize a slope. Placing the decreases a few stitches from the edge forms a decorative detail, called fashion marks or fully fashioned shaping marks, that are visible on the right side of a garment. The cardigan below shows these marks along the front borders.
Decreases are usually worked on the right side of the knitting every other row, reducing one stitch at a time. Sometimes instructions ask you to decrease stitches every row, therefore decreases must be made on the wrong side of the work. When decreasing on the wrong side, maintain the same slant direction as the decreases on the right side of the knit fabric.
Usually one or two stitches are decreased at a time. I’m not a fan of decreasing more than two stitches at a time when shaping waist areas, armholes, or sleeve caps. I find the fabric pulls in creating a bumpy or slightly puckered look. For most projects, I place decreases one or more stitches within the sides to avoid uneven edges, which makes the pieces easier to sew together.
Common Single Decreases (dec)
Working two stitches together is the easiest decrease to make, and can be done right at the edge or within a few stitches from the edge. Decreasing the two edge stitches gives a step-like appearance, but the decrease will not be seen when garment pieces are sewn together.
Knit two together (K2 tog): Insert your right hand needle into the next two stitches on the left needle as if to knit (knitwise). Knit these two stitches together as one. Knitting two stitches together creates a right slant on the right side of the knitting.
Knit two together through back loop (k2 tog tbl): Insert the right needle through the back loops of the next two stitches on the left needle. Knit these two stitches together. This may seem awkward at first. A left slant is made by knitting two together through the back loop.
Purl two together (P2 tog): Insert the right needle into the front loops of the next two stitches on left needle as if to purl (purlwise). Then purl these two stitches together as one stitch. Purling two stitches together also creates a right slant on the right side of the knitting.
Purl two together through back loop (p2 tog tbl): With the right needle behind the left needle, insert it into the back loop of the second stitch, then through the back loop of the first stitch on left needle. Purl these two stitches together, and as with k2 tog tbl, it may feel awkward. A left slant is created by purling two together through back loop.
Slip, slip, knit (ssk): This decrease slants to the left on the knit side or right side of the work. Slip two stitches knitwise one at a time from the left needle to the right needle. Insert the left needle into the fronts of the two slipped stitches on the right needle from left to right, and knit them together by wrapping the yarn around and pulling the loop through to the front, dropping the two slipped stitches.
Slip, slip, purl (ssp): A left slant appearing on the knit side can be made with purl stitches on the wrong side. Slip two stitches knitwise, one at a time from the left needle to right needle. Return these two stitches to the left needle, leaving them twisted. Purl these stitches together through the back loop.
Slip, knit, pass slipped stitch over (skp) (also sl1,k1,psso):This method of decreasing slants to the left on the knit side. Slip one stitch knitwise. Knit the next stitch. Insert the left needle into the front of the slipped stitch and lift this stitch over the one just knit (pass the slipped stitch over the knit stitch or psso) and off the needle.
Slip, purl, pass slipped stitch over (sl1, p1, psso): This decrease is worked on the purl side and the stitches slant to the right on the face or knit side. Slip the next stitch on the left needle purlwise, then purl one stitch. With the left needle, pass the slipped stitch over the purled stitch and off the right needle.
The above are all single decreases and the most common. There are double decrease methods that work with three stitches, but these are not addressed in this post. They are worked very much like the single decreases, and once you master the basic ones these double decreases are easy to work. Most pattern instructions contain a glossary of the decrease methods used for the project.
A note on slipping stitches: Slipping a stitch is simply passing it from the left needle to right needle. When slipping a stitch knitwise, the stitch twists, but slipped purlwise, the stitch remains untwisted. If the pattern instructions do not specify which way to slip, then slip purlwise, except when decreasing stitches, slip them knitwise. To slip knitwise, insert the right needle into the stitch as if to knit and slide it onto the right needle. To slip purlwise, insert the right needle into the stitch as if to purl and slide it onto the right needle.