Beginner Basics: How to Work a Tubular Cast On
Because the Tubular Cast On is very stretchy, it’s ideal for a sweater's bottom ribbing and cuffs.
Using waste yarn (shown in green) cast on half the number of stitches you need and work a few rows in stockinette. Then, using the working yarn (white), purl one row and work a few more rows in stockinette.
With the wrong side facing, insert your right-hand needle into the first purl bump in the first purl row (below the last line of green purl bumps).
Lift the loop onto your left-hand needle and knit it through the back loop.
Continue across the row, alternating stitches: purl a stitch, pick up and knit the next purl bump through the back loop, purl a stitch, and so on.
When you're finished, continue knitting the sweater according to the pattern. There are no tight stitches to stop the edge from stretching.