Just be sure they are located where you can water them. Most varieties require lots of water during our hot dry summers. Outside of that, just a normal deep planting hole with the rock removed......you might have to bring in some better soil if it is too rocky. I bet it is good growing soil. Deep mulch would be a good idea too to hold in the moisture.

You will find lots of info on amending the soil to make it more acidic however, that's not necessary to make them thrive. People just amend the soil to change the color of the flowers. More acidic soil will make the flowers turn blue instead of pink (depending on what kind of hydrangea you're planting). It wouldn't matter with white flowered varieties. They do need extra water in mid to late summer when it's hot and dry as Glenda said.