Looking to mix it up a little? Have some fabric leftovers that need using up? Want a summer project that doesn't stick to your sticky sweaty fingers the way wool yarn does? Try knitting up a rug with fabric strips!
At its heart, knitting a rag rug with fabric strips is a simple matter. You turn fabric into strips, join them, wind them into a ball, and knit a big honkin' rectangle of garter stitch. (This is also a perfect summer knitting, in the sense that if you do it outside, it's much easier to deal with the clean-up from all the millions of fraying bits that fly loose.)
How do you cut the strips?
If you are using a woven cotton fabric, it's easy: just nick the edge of the fabric with your scissors and then tear. Aim for strips that are between ½ an 1" across.
How do you join the strips?
The easiest way is to just knot them together at the ends. If you want to get fancy, you can sew them together with a serger, or just tack them together by sewing an X. Or you can cut a slit in the end of both strips, slip one end through, and pull it tight. (Note: these methods create bulk at the join, of various thicknesses.)
That sounds like too much work.
If that's the case, try cutting them in a clever zig-zag pattern, so that you end up with one long strip out of one long swath of fabric. Here's a tutorial. (Note: this method creates "flaps" of fabric along the length of the strip.)
What size knitting needle?
It depends on how wide your fabric strips are, and how stiff you want your rug to be… start with at least a size 19. Maybe bigger. Lion Brand has some giant knitting needles you can buy at big box craft stores in the #36 range.
Most people start with a rectangular garter stitch rug. Cast on as many stitches as you can, then garter stitch away. If you want to get fancier, or you want a rug that is wider than the number of stitches you can cast onto your needles, you can knit strips, and sew them together with a contrasting color.
It has occurred to me to try something like Frankie Brown's Ten Stitch Blanket with rag strips, but back-and-forth instead of in a spiral. However, I'm not sure if it's feasible to be picking up stitches and decreasing stitches on each row when you're knitting with something as non-compliant as fabric strips. Food for thought, though!