Re: prepping hemp, can I air dry?
You can use detergent on both. Remember to use about 1/2 what you would use for regular laundry. I would use soap on the first wash and after just use water.
IF you plan to hang dry, I wouldn't think that would be a problem to prep them that way. Prefolds I think it was 6 wash/dry cycles to prep them. Hopefully someone else will chime in because I only did cotton.