have never tried hydrangea, but have had luck with other plants by gently filling in around roots with wetted perlite over top of lava, taking rooted cuttings directly from hydroponics to perlite. just don't pack the perlite too tightly. re-pot as usual after that, i reckon. c-p

The reason you were able to root in water and not a perlite mix was because the humidity of the water kept the cutting from drying out. When the roots you have are at least one inch long take a pot of potting soil partly filled place the rooting cutting on the soil and fill the rest of the pot around the cutting, firming it around the roots. Put the pot in a bath of water to soak it good, then remove from the water. Keep the pot in the shade and watch for wilting. If it wilts cover with plastic and try again the next day. When it does not wilt without the plastc you have succeeded. Al