|CARD WITH CROCHET EDGE|
I've pierced holes down the side with a single needle tool, a reasonable distance from the edge. This was a precaution in case the card tore. As it happened, this was unnecessary as everything stayed put. There are lots of ways to space holes evenly, but I used the most "low tech" which was simply to pierce them against a metal ruler at regular intervals.
I blanket stitched along the holes, so there was a larger space into which to crochet, and then just made up the edging as I went along.
If I was doing this "properly" I would have used a much finer cotton, and probably either worked out or copied a more decorative edging (there are lots of free patterns online). You don't have to confine crochet to the edges of cards - crochet motifs can be used as the main focus (flowers, snowflakes, small doileys etc), and you can also add borders to simple shapes.