Composted manure: I assume that is something like Black Kow? Potting mix: I assume something like Miracle Grow or Scotts? How deep to dig the hole for the azaleas? I assume not very deep at all ...

How can I amend the soil properly? I have bags of topsoil, mushroom compost, and Black Kow manure. A Hydrangeas can be wonderful, long-lived shrubs but even they have a lifespan and yours clearly ...