Acid soil is a dynamic process of leaching - you can't just expect to make it.!

What I do when planting Rhodo's at the edge of their Ph range is make raised beds with loads of compost and bracken peat and 20 or 30% existing soil and plant them on that, then mulch around them. Plant a rhodo where its roots are at the surrounding soil level or lower and it'll start to go Chlorotic. For potatoes you'll have to make one mighty tall raised bed! Maybe best off with old fert. drums