Im looking to turn my lawn more acidic in order to accomodate my apple trees to their full nutritional potential and also create a raised bed of more acidic soil for some blueberries. Various ph tests from around my garden show some parts as alkaline and others as borderline neutral with the barest of acidity.
I have read that apple trees prefer soil to be somewhat acidic, no less than ph 5.5, and that blueberries prefer between ph 4.5 and 5.5.

I have purchased some sulphate of iron and am looking for some advice.

How often with how much per square yard/meter should i apply? Could this particular sulphate have some adverse affects on my lawn, blueberry or apple tree roots?
I have also heard that it helps prevent certain fungus', diseases and weeds, which seems beneficial to my growing fruit garden.

Im from the North West .(Just incase it matters )
Thanks!