Not sure what happened to my Incrediball hydrangea. I am in Zone 7. Planted the baby last July, I believe. Originally had 3 stems growing. Two got broken in the hurricane last August but the other one did well until frost, then died off like the other hydrangeas did. It started to come back to life last month but suddenly last week, all the leaves on the only remaining 2′ sprout all wilted. I cut it down a little in hopes of other shoots growing out but nothing yet. This one gets mostly direct sun with just a tad of shade in the p.m. Soil is just regular soil. When I plant babies I put a little peat moss and mix it in. Hope that helps. I want to order another one with my order this weekend, so if there is something ‘not right’ with what I did, please let me know.
A newly planted hydrangea takes a little while to settle in. It sounds like you’ve not done anything wrong. Annabelles might like a bit more afternoon shade; morning sun is always the best, especially in a Zone 7 setting. Regular garden soil is just fine. They need nothing special except for even moisture. As to why the first one did not survive, I can only guess that possibly the roots were damaged in the storm. Sometimes plants will put forth every effort to survive after damage but just give up. Just try one again. I don’t think you’ve done anything “wrong.”
Good luck with the Incrediball. I have one, and it’s a great plant.