I found the beast way to root cuttings is to wrap the upper half in grafting tape, and bury lower half in pro mix, had like 90% success or u can use perlite with vermiculite, the way u are doing will work also but if kept together the roots get knotted up and they are very fragile, I've started cuttings that way, and at first sight of roots I move to pro mix, cause if kept together and roots knot trying to unknot them you will pull all roots off, and I keep them indoors in indirect sunlight.