Holly, often plants rooted in water don't transplant to soil easily is because their roots are very fragile from rooting in water.
I've had much better success using Perlite with water. I fill a container such as you would use to root in water with Perlite, strike my cuttings and place them in the Perlite then fill with water. Keep enough water to keep the Perlite very moist but not "floating". I leave them till there is a "Mass" of roots . It makes for much stronger roots, and when you transplant just leave what ever Perlite sticks to the roots on the plant and pot up as usual.
