How are they hemmed to begin with?
I try to redo any shortens as close to original as I can.
I've had a jersey jumpsuit dropped off today which I need to shorten. Originally they have coverstitch finished hems so I'll twin needle these when I do them. I probably won't overlock the raw edge. No point. Just makes the cut edge a bit bulkier/wavier. Sometimes I'll turn a double hem so there's no raw edge left inside, but not if it's going to make the hem too heavy and bulky.
Sometimes, but not very often, jersey trousers might have traditional 'hand' finished hems (finished with a blind hemmer) in which case I'll overlock the raw edge and hand stitch the hem up. These are usually on heavier, sturdier weight jersey as opposed to the flippy-floppy stretchy jersey.
Sandra.
xxx