Turning to my copy of
"The Knitting Answer Book" by Margaret Radcliffe, there's at least 2 Q and As that apply:
Q: When i bind off, the edge is always too tight. What should i do?
A: This happens because the stitches need to lie sideways across the edge of the knitting, but knit stitches are wider than they are tall, so the bound-off stitches naturally pull in a little compared to the stitches below them. Here are some tips that may help.
- Use a larger needle (or crochet hook) while binding off. It automatically makes the stitches a tiny bit bigger, allowing them to stretch a bit more across the edge. Be sure to form each stitch on the straight part of the needle, instead of on the needle tip.
- Loosen up. Each time you bind off a stitch, lift the right needle up a bit, pulling the stitch looser, before you knit the next stitch. If you are a firm knitter, stifle the urge to tighten each stitch as you go.
- Try a different bind off. The Yarn Over Bind Off, Sewn Bind Off, and Tubular Bind Off are all looser and stretch mroe than the Basic bind Off.
Q: Which bind off is the most stretchy?
A: The Tubular Bind Off is, if you are careful to work it loosely, although it tends to stretch out of shape. The Yarn Over Bind Off is stretchy and retains its shape better.
If you google, you should be able to find instructions for these different bind offs; they are also in the book mentioned, but have graphical content i can't translate here.