I have rooted many cuttings of my Ivy, which is still doing great after many months and has got bigger. What I did, as I had the same questions you are asking, is to add slowly soil to my water. A little by each week. As it's starting to get like a soil "pulp", that is the time I plant my rooted cuttings to the ground. I don't water them afterwards immediately, I just pour into a hole my pulp, the cuttings and adding the new soil.
Good luck with your cuttings, hope you make new plants out of them!
