Changing soil pH - rhodos.

My apologies if this has been covered before - I've done a brief
search and not found anything.

I've an area of some 3m x 6m that I want to plant with rhodos and
azalias. It's currently reading around 7.0 across the plot - ie
neutral. Do I attempt to adjust the whole bed soil and with what, or
should I just dig big planting holes and mix in a lot of peat ?

Many thanks