Hydrangea cuttings will do best in a sterile, moisture-retentive, well-draining rooting medium for moisture, support of the stems, and to discourage fungal disease. Vermiculite, perlite, coarse sand or a commercial soilless potting mix all work well. An easy way to lose cuttings is to place them in an overly wet, heavy rooting medium.

The plastic bag covering is recommended to maintain the humidity the cuttings need, pot should be in bright light but not direct sun so the cutting doesn't fry.

I have one that I grew from a cutting in a florist shop. I think it's a starburst? It rooted very easily in a pot of regular potting soil, not covered, no special care.